Citizen's Guide to Where Your Water Comes From

CITIZEN’S GUIDE TO

Where Your Water Comes From SECOND EDITION

P R E PA R E D B Y W AT E R E D U C AT I O N C O LO R A D O

Citizen’s Guide to Where Your Water Comes From This Citizen’s Guide is part of Water Education Colorado’s series of educational booklets designed to provide Coloradans with balanced and accurate information on a variety of water resources topics. Guides in the series cover: Colorado water law, water quality, water conservation, interstate compacts, water heritage, groundwater, Denver Basin groundwater, transbasin diversions, and Colorado’s environmental era.

View or order any of these online at www.watereducationcolorado.org.

STAFF Jayla Poppleton Executive Director

BOARD OF TRUSTEES Lisa Darling President

Jennie Geurts Director of Operations

Gregory J. Hobbs, Jr. Vice President

Stephanie Scott Leadership Programs Manager

Gregg Ten Eyck Secretary

Scott Williams Education & Outreach Coordinator

Alan Matlosz Treasurer

Meg Meyer Development Coordinator Jerd Smith Fresh Water News Editor Caitlin Coleman Headwaters Editor & Communications Specialist

Eric Hecox Past President Perry Cabot Nick Colglazier Sen. Kerry Donovan Jorge Figueroa Greg Johnson Julie Kallenberger Scott Lorenz Dan Luecke Kevin McBride Amy Moyer Lauren Ris Rep. Dylan Roberts

Water Education Colorado thanks the people and organizations who assisted in the preparation and review of this guide.

Travis Robinson Laura Spann Chris Treese Brian Werner

Authors: Caitlin Coleman and Nelson Harvey Editor: Caitlin Coleman Design: Chas Chamberlin

THE MISSION of Water Education Colorado is to promote increased understanding of water resource issues so Coloradans can make informed decisions. WEco is a non-advocacy organization committed to providing educational opportunities that consider diverse perspectives and facilitate dialogue in order to advance the conversation.

Copyright 2019 by the Colorado Foundation for Water Education DBA Water Education Colorado. (303) 377-4433 WAT E R E D U CAT I O N C O LO R A D O.O RG

ISBN: 978-0-9857071-5-6

COVERS: ADOBE STOCK

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Colorado’s Geography and Natural Water Sources . . . . . . . . . . . . . . . . . . . . . . 4 Colorado’s Built Hydrology and Administration . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Hydrology and Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Precipitation and Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Drought . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Climate Change and Aridification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

108°

104°

HIGH

SAND WA S H

Fort Collins

Forest Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Insect Infestations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wildfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Human Disturbance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10 10 10 11

Infrastructure and Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Legal Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Transbasin Diversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Moving and Storing Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Municipal Treatment and Delivery Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Agricultural Diversion Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Groundwater Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Water Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Resiliency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12 12 12 13 14 16 18 18 18

Colorado’s River Basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Gunnison River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Colorado River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Yampa/White/Green River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

North Platte River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

South Platte River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Republican River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Arkansas River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Rio Grande Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

PLAINS Dolores/San Juan/San Miguel River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20 20 20 20 21 22 23 23 24 24

Sterling

Greeley

Steamboat Springs

Colorado’s Groundwater Aquifers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

South Platte Alluvial Aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

EXPLANATION HIGH San Aquifers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I N S Valley Structural P L ALuis basin boundary Denver Basin Aquifers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Multiple sedimentary bedrock aquifers High Plains Aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

40°

Glenwood Springs

Denver

EAGLE

DENVER

CEANCE

Dakota–Cheyenne aquifer

Colorado Springs

Pueblo

D A KO TA – CHEYENNE

Lamar

OX

38°

Alamosa

Durango

SAN

RATO N

JUAN

HIGH PLAINS

Trinidad

108°

104°

0

100 Miles

26 26 26 26 27

Looking ForwardHigh Plains . . . . aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Gunnison Montrose

6 6 6 7

100 meter Digital Elevation Model courtesy of U. S. Geological Survey

Introduction

I

mportant as it is, for many the question of “where does your water come from?” has a simple answer: “From the tap.” Yet, the water for your morning shower may have traveled more than 200 miles, from melting snowpack to a high mountain reservoir, down a river, through tunnels, treatment plants and pipes. Perhaps it even moved through someone else’s home or was used to irrigate a field before being treated and making its way to your house. Or it may have been pumped from 2,500 feet below the earth’s surface, tapping ancient water molecules that have been contained in underground aquifers since before the Stone Age. This Citizen’s Guide to Where Your Water Comes From helps explain how weather patterns, rivers and aquifers produce a native water supply, and also introduces readers to the intricate systems Coloradans have developed, out of necessity, to deliver water where it’s needed. End uses for water include not just municipal water uses like drinking and irrigating urban lawns and parks, but also agricultural irrigation, industrial uses like energy extraction and cooling, recreational uses like rafting and fishing, environmental uses such as providing aquatic habitat and functioning riparian corridors, and others. This guide also looks at what happens to water as it is used, often again and again, as it makes its way through both natural and human-induced cycles.

Colorado’s Geography and Natural Water Sources Colorado’s geography and water systems make it unique. The Continental Divide rises high, nearly halving the state, yielding massive snow-capped peaks and creating distinct drainage basins. Colorado is famous for its mountains. With an average altitude of about 6,800 feet above sea level, Colorado has the highest average elevation of the 48 contiguous U.S. states, yet 40 percent of its land area is composed of the vast Eastern Plains. The plains gracefully slope up from Colorado’s borders with Kansas and Nebraska to the base of the Rocky Mountain foothills. And there, as the plains approach the mountains, resides more than 85 percent of Colorado’s population.

Yet up to 85 percent of Colorado’s water accumulates west of the Continental Divide. As the prevailing winds blow west to east, the state’s mountain ranges force moisture-rich air to rise and condense—the main dynamic behind precipitation. The mountains’ varying elevations also create wide variations in precipitation within small distances. For the most part, the eastern side of the Rocky Mountains is in a rain shadow as moisture is mostly wrung 4 • WAT E R E D U C AT I O N C O L O R A D O

out of the atmosphere by the time it passes Colorado’s Western Slope.

Snow falls and snowpack accumulates on high peaks during the winter months, creating a natural reservoir that stores moisture throughout the winter. As the warmth of spring and early summer strikes, that snow begins to melt. Water runs off the slopes and flows down the terrain—divided by topography into distinct drainage basins—collecting and creating the headwaters of four of the nation’s great rivers: the Colorado, the Platte, the Arkansas and the Rio Grande.

While about 85 percent of Colorado’s annual precipitation is intercepted and consumed by native vegetation growing in forests and grasslands, according to the 2003 article, An Alternative Perspective on Water Use in Colorado, from the Colorado Water Center at Colorado State University, spring runoff provides the primary source of water for most of the state’s population and for its industries, including irrigated agriculture.

Colorado’s Built Hydrology and Administration In order to make sure water is available when needed and to control deluges that

might otherwise cause damaging floods, Coloradans, with the help of federal agencies like the U.S. Bureau of Reclamation, have built nearly 2,000 storage reservoirs and dams, altering the natural system. Although snowpack provides an excellent natural reservoir, the majority of runoff occurs over just a few short months, typically peaking in late May or early June. Irrigators, municipalities, and rivers themselves are drier and have higher water demands in the heat of late summer. Storage helps ensure that water is available all year, even when natural runoff has ceased.

This is not the only manipulation to the system. Coloradans have engineered the state’s watersheds and heavily administered water right decrees in order to move water where it’s needed. Although most precipitation falls on the Western Slope, the state’s urban centers and the bulk of the population lives along the Front Range, while rich soils and long growing seasons are also found in the more arid Eastern Plains.

For years, people have dug their way out of this challenge by diverting water and channeling the resource. On the Eastern Slope, including Front Range cities and Eastern Plains farms, Coloradans have relied heavily on waters from the Colorado River Basin, creating tunnels and intricate systems that transport water from the headwaters region near the Continental Divide to other parts of the state through transbasin diversions. As a result, if you live in Denver in the South Platte Basin, for example, your water comes from a combination of sources including the Blue River, Williams Fork River, and Fraser River high in the Colorado River Basin on the state’s Western Slope, and from the South Platte River on the Eastern Slope.

Because water is not always available at the time and place it is needed and there is often not enough water to meet all demands, the state’s water resources are heavily regulated and administered.

Colorado’s prior appropriation doctrine is the legal framework that regulates the use of surface water and tributary groundwater connected to streams. The prior appropriation system creates water use priorities on a “first in time, first in right” basis, where older water rights get their

Blue Mesa Reservoir stores water in Colorado’s Gunnison River Basin before it is sent downstream to the Colorado River. To the northwest, precipitation in the West Elk Mountains will eventually bring flows to the North Fork of the Gunnison River.

water first in times of scarcity. It is used to administer water when there is not enough to meet all demands. The Colorado Division of Water Resources administers water rights, issues well permits, and works in other ways to ensure that Colorado’s water is fairly and safely administered, accounted for, and used within the legal system. While the Division of Water Resources tracks water quantity, the Colorado Department of Public Health and Environment’s Water Quality Control Division and U.S. Environmental Protection Agency regulate water quality, ensuring that drinking water systems, discharges, and streams meet public safety requirements for the environment and for human health.

When it comes to protecting the fish and wildlife that rely on the state’s streams and reservoirs, the U.S. Fish and Wildlife Service and Colorado Parks and Wildlife both look to protect and restore habitat and endangered and threatened species, and work with other agencies to ensure new ADOBE STOCK

Up to 85% of Colorado’s precipitation accumulates on its Western Slope The natural environment intercepts and uses 85% of precipitation in Colorado

projects—from developments and roads to reservoirs—don’t impact fish and wildlife.

In addition to careful administration and regulation of Colorado’s limited water resources, water supply planning helps the state and individual municipalities prepare for dry years and a future where there may not be enough supply to meet all competing demands. The Colorado Water Plan, published by the Colorado Water Conservation Board in 2015, integrates work done by Coloradans across the state in every river basin to look ahead and develop solutions that could meet the future water needs of a growing population while still supporting the existing water uses Coloradans value and rely on. The water plan is a roadmap to support healthy watersheds, the environment, recreation and tourism, thriving cities, and viable agriculture. The plan aims to balance many water demands with what is expected to become a more limited supply of water, according to most climate models.

C I T I Z E N ’ S G U I D E T O W H E R E Y O U R WAT E R C O M E S F R O M

•

5

Hydrology and Climate

C

olorado’s water arrives in a seasonal cycle that starts with snow accumulation through late fall, winter and early spring, followed by spring melt and runoff, then rainstorm activity in the summer.

Variations occur each year, and in any given year some part of the state can be in drought while another enjoys water abundance.

Hydrology—the science of water flux in the environment—explains how water evaporates from sources on the earth’s surface, rises into the atmosphere, condenses, and falls to the earth’s surface as precipitation. It also describes how water moves from its point of origin to a destination, whether in a groundwater aquifer or river system.

After precipitation occurs and snow melts, the water runs into streams, lakes and reservoirs, and infiltrates soil and rock, increasing soil moisture and recharging aquifers. Nearly all of Colorado’s water supply originates from precipitation because few rivers flow into the state. Rather, Colorado has the distinction of being known as a headwaters state, with its mountains the source of major rivers that supply many millions of people in 18 other states as well as Mexico.

Surface water and groundwater may be diverted or pumped and used for homes, agriculture, recreation, environment and industry. Water that is not fully consumed by each use returns to streams or aquifers and will be diverted for other uses as it makes its way to downstream states and toward the Atlantic and Pacific oceans. Along the way, some water evaporates back into the atmosphere, where the cycle begins anew.

Precipitation and Temperature Statewide average annual precipitation is 17 inches—ranging from just 7 inches in the middle of the San Luis Valley to over 60 inches in some mountain locations, according to the National Oceanic and Atmospheric Administration.

In the winter, snow falls on Colorado, building up as snowpack in high elevations, a natural form of water storage. In lower elevation areas, snow melts soon after it falls. Heavy snowpack in Colorado’s mountains generally increases during the early spring as a result of storms originating in the Pacific Ocean and moving from west to east. As those air masses rise over the mountains, if they contain enough water vapor, that vapor will condense and fall as precipitation mostly on westward-facing slopes. In the mountains, snowfall may reach as much as 600 inches in a season, while at lower elevations snowfall is much less.

When warm, moist air from the south is carried northward and westward into Colorado’s higher elevations, typically from April through September, precipitation occurs over the eastern portions of the state.

6 • WAT E R E D U C AT I O N C O L O R A D O

Moist air from the southwest finds its way to southern and western Colorado through the southwest “monsoon” season from July through September.

Just as it does with precipitation, elevation affects all aspects of Colorado’s climate. In general, temperatures decrease at higher elevations. On Colorado’s Eastern Plains, summer daily maximum temperatures are often 95 degrees Fahrenheit or above— temperatures at 100 degrees Fahrenheit and higher have been observed at all plains weather stations. Winter extremes on the plains often fall between zero degrees and -15 degrees Fahrenheit, though have reached even more extreme lows. In low mountain valleys, summer highs are typically in the 70s and 80s and lower, between 50 and 70 degrees Fahrenheit, on the highest peaks— while summer nighttime temperatures run cold, often in the 40s, and may dip below freezing. In the winter, most mountain areas see occasional lows dropping below zero degrees—most winters bring a few nights that dip to around -30 degrees Fahrenheit, with even colder extremes occurring occasionally. Higher temperatures during the summer months can result in increased

evaporation rates and increased water demand for plants. Higher temperatures during the winter and spring months can translate to less snowmelt—with snow evaporating or melting during the winter— and earlier runoff.

Drought During years with low precipitation, drought can develop and result in water shortages that affect reservoir storage as well as soil moisture and streamflows.

According to the Colorado Water Conservation Board, it is rare for the entire state to experience drought at the same time, however single-season droughts affecting some portion of Colorado at any given time are common.

In a short-term drought, a combination of low precipitation and high temperatures, which exacerbate drought symptoms through increased transpiration rates for plants, leads to a soil moisture deficiency. As droughts deepen and become longer term, plants become stressed, streamflows recede, and reservoir levels shrink. The result can be far-reaching impacts to the economy and the environment, including agriculture, recreation, tourism, fish and wildlife, and all else that depends on water. Extreme drought conditions can result in emergency and disastrous conditions, including loss of crops, low streamflows, increased stream temperatures that result in fish kills, and an increased threat of wildfire.

The state monitors drought and water supply in several ways. The Governor’s Water Availability Task Force, led by the Colorado Water Conservation Board and Colorado Division of Water Resources, meets throughout the year to monitor water availability by tracking snowpack, precipitation, reservoir storage, streamflow and weather. When drought conditions reach predetermined levels, task force chairs recommend that the governor activate the state’s Drought Mitigation and Response Plan. Actions laid out in the plan depend on drought severity. Steps may include increased monitoring, declaring a drought emergency, requesting a presidential declaration, and implementing recovery operations.

A second group of climate scientists meets weekly and releases summaries of

those meetings. The same group comes together monthly for publicly accessible drought assessment webinars. These National Integrated Drought Information System (NIDIS) meetings are arranged through the Colorado Climate Center, with recordings shared on the Colorado Climate Center’s website. The NIDIS group monitors drought conditions more frequently than the task force. The group also makes recommendations to the U.S. Drought Monitor.

Colorado experienced major historic droughts culminating in the years 1934, 1954, 1977, 2002, 2012 and 2018. However, unlike early drought years, the 2002, 2012 and 2018 droughts are not viewed as standalone events. Scientists and water managers are referring to it as the result of a multi-decadal drought period, signaling what may be a transformation of Colorado’s climate.

Precipitation in Colorado Average Annual Precipitation, 1981–2010 The average annual precipitation in Colorado varies with the state’s topography, with some regions receiving less than 8 inches of precipitation and others receiving more than 50 inches each year.

This map is based on data from 1981-2010.

Climate Change and Aridification Colorado has warmed by about 2 degrees Fahrenheit since the early 20th century and the path is set for unprecedented warming by the end of the 21st century, according to the 2019 National Oceanic and Atmospheric Administration’s (NOAA) State Climate Summary for Colorado. Future levels of warming will depend largely on future greenhouse gas emissions. According to the 2014 report Climate Change in Colorado by the Western Water Assessment at the University of Colorado-Boulder in partnership with the Colorado Water Conservation Board, all climate models project statewide warming between 2.5 degrees and 6.5 degrees Fahrenheit by 2050.

No significant trends have emerged to predict how precipitation could change as a result of climate change. However, according to NOAA, extreme precipitation events are projected to increase, which could lead to more flood events. The Climate Change in Colorado study reports that many climate models project an increase in precipitation during winter months and a decrease in the summer.

Due to warming, Colorado’s snowline is expected to shift, raising the lowest elevation at which snow falls. In other words, lower elevations could see more PRISM CLIMATE GROUP

<8

8–10

10–12

12–14

14–16

16–18

18–20 20–25 25–30 30–35 35–40 40–45 45–50

>50

Month of Maximum Average Precipitation, 1981–2010 The month of maximum precipitation also varies across the state—Colorado is so diverse that every month brings peak precipitation somewhere. Spring storms dominate over the northern Front Range and northeastern Colorado, winter precipitation dominates over the high elevations, and late-summer monsoons bring moisture to southern Colorado. This map was produced by Colorado Climate Center and is based on data from 1981-2010.

JAN

FEB

MAR

APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

C I T I Z E N ’ S G U I D E T O W H E R E Y O U R WAT E R C O M E S F R O M

•

7

Observed and Projected Colorado Average Annual Temperatures, 1950–2070 Observed temperatures through 2018 (bars) reveal that Colorado’s climate has warmed about 2 degrees Fahrenheit over the past 30 years. Projected temperatures through 2070 from 36 global climate models under a medium-low emissions scenario and a high emissions scenario all show further substantial warming. By 2050, a “normal” year in Colorado is expected to be up to 3 degrees Fahrenheit warmer than 2012, the warmest year on record.

Observed and projected temperature change, ° Fahrenheit

10°

Median projection, high emissions scenario

8°

6°

4°

Median projection, medium-low emissions scenario

2°

0°

1971–2000 AVERAGE

–2°

PROJECTIONS High emissions scenario (RCP 8.5) Medium-low emissions scenario (RCP 4.5)

–4° –6° 1950

1960

1970

1980

1990

2000

2010

2020

2030

2040

2050

2060

2070

Source: Adapted and updated from Lukas et al., Climate Change in Colorado, 2014 Observed data: NOAA NCEI; http://www. ncdc.noaa.gov/cag/; Model data: https://gdo-dcp.ucllnl.org

Colorado July Palmer Drought Severity Index (PDSI), 1900–2018 The Palmer Drought Severity Index uses temperature and precipitation data to estimate relative dryness and quantify long-term drought. The 1970–1999 average was +0.9, or wetter than normal, while the 2000-2018 average is –1.7, or drier than normal.

6

PDSI

4

1970–1999 AVG.

2 0

DROUGHT

–2

2000–2018 AVG.

MODERATE SEVERE EXTREME

–4 –6 –8 –10 1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

2010

2018

Source: Adapted and updated from Lukas et al., Climate Change in Colorado, 2014; Data: NOAA NCEI; http://www.ncdc.noaa.gov/cag/

Colorado April 1 Snow-Water Equivalent, 1968–2018 There is an apparent long-term declining trend in spring snowpack; in the 21 years from 1998 to 2018, 16 years were below the long-term median.

PERCENT OF MEDIAN

160 140 120 100 80 60 40 20 0

1968

1973

1978

1983

1988

1993

1998

2003

2008

2013

2018

Source: NRCS Colorado Snow Survey, https://www.nrcs.usda.gov/wps/portal/nrcs/main/co/snow/

8 • WAT E R E D U C AT I O N C O L O R A D O

moisture falling as rain rather than snow and an increasing risk of floods from rain-on-snow events. This change would also reduce the amount of water stored in snowpack throughout the winter. Colorado’s spring snowpack and runoff have likely already declined due to climate change. A 2018 study published in the journal Climate and Atmospheric Science analyzed 699 snow monitoring sites across the West and found that since 1915 the “snowwater equivalent,” or the amount of water contained in snowpack, as measured each year on April 1, has declined by 21 percent.

Warming is also projected to cause snowpack to peak earlier, which would result in earlier snowmelt and runoff, reducing overall water availability during the months when it is most needed. This trend has already been observed, creating challenges for water managers and water rights owners who count on the historical timing of runoff and streamflows. The shift to earlier runoff might necessitate the construction of new storage reservoirs or the rethinking of water management to adjust to unprecedented changes in flows.

Higher temperatures could also mean more snowpack would be lost to sublimation, skipping a liquid melt state and going directly to water vapor on warm days, resulting in reduced runoff and less water available to replenish reservoirs.

Additionally, warmer weather could result in a lengthened growing season in which irrigators would need to use water earlier and for a longer period of time, resulting in more water demand. Irrigators and water users might also see that high summer temperatures lead to heightened evaporation and evapotranspiration rates, necessitating the use of more water to account for losses and to keep crops thriving.

According to a 2017 paper in the journal Water Resources Research, native flows in the Colorado River Basin have fallen by about 18 percent since 2000, with about one-third of that reduction due to the higher temperatures brought on by climate change. Factors like increased sublimation and longer growing seasons have caused Colorado River runoff to decline by about 4 percent for every degree Fahrenheit of warming in the basin.

At the same time, the intensity of droughts is projected to increase according to the 2015 Colorado Climate Change Vulnerability Study by the Western Water Assessment and Colorado State University. High temperatures will result in an increased rate of soil moisture loss, leading to more intense drought conditions.

Severe drought along with less summer precipitation will increase the risk of wildfire occurrence and severity.

The Colorado Climate Plan provides a set of policy recommendations to mitigate greenhouse gas emissions and to increase Colorado’s preparedness for climate change impacts. The plan identifies how climate

Recent Droughts

2002

The 2002 drought got its start in fall of 1999, when conditions were dry across most of Colorado. The following years also brought below-average snow accumulation and above-average temperatures, resulting in high evapotranspiration rates, depleted soil moisture and low surface water supplies. By spring of 2002, no precipitation was falling, temperatures climbed to record highs, and snow melted or evaporated quickly. Fire danger was already high by April 2002 and dry weather continued throughout the spring, leading to low streamflows, municipal watering restrictions, and numerous fires breaking out. June brought the most severe fire of the season, the Hayman Fire, which erupted southwest of Denver and grew to become the largest documented fire in Colorado at the time, burning more than 137,000 acres. Ranchers around the state moved or sold off their herds and farmers suffered. The pattern continued until August yielded thunderstorms that brought heavy rainfall to parts of the state. Humid weather continued into September and drought began to ease.

change is projected to occur in the state and how it will affect the key sectors of water, energy, transportation, public health, agriculture, tourism and others. It identifies measures that are being implemented to prepare for warming, along with goals and recommendations to help each sector adapt and mitigate impacts.

southwestern part of the state, and as the dry summer dragged into fall, they opted to keep the plan in place. Among the regions hardest hit was the Yampa Valley. The river, once known for its legendary, generous streamflows, for the first time ever saw water use curtailed as flows tanked in the face of the relentless heat. The Front Range and parts of the Eastern Plains had more water than the rest of the state, although the hot temperatures took a toll. Various records were set and three wildfires, the Spring Creek Fire, 416 Fire, and MM 117 Fire, made it onto the state’s top 10 list for largest wildfires on record.

While there was some hope that an El Niño would bring more moisture to the state in late fall and winter, the state’s snowpack slipped below average at the end of calendar year 2018. Early 2019, however, brought a series of snowstorms. By March of 2019, statewide snowpack was more than 140 percent of average—more than two times higher than it was at that time in 2018.

Sources for Drought and Climate Data

2012

The 2012 year began in a similar way to 2002, with about half of the state already designated as experiencing drought conditions. Temperatures from February through May were above average and precipitation totals were below normal.

Snowpack melted early and streamflows were low. By the end of May, 100 percent of Colorado was in drought, including the mountains that supply about 80 percent of the state’s water supply. Soil moisture was low as early as spring planting times. June temperatures soared, setting many daily and all-time records. Numerous major wildfires and grass fires broke out during the summer, including the massive Waldo Canyon and High Park fires, which burned 18,247 acres and 87,284 acres respectively close to population centers, destroying hundreds of homes. The Waldo Canyon Fire was the most costly in the state’s history, claiming two lives, destroying more than 345 homes, and resulting in more than $453.7 million in insurance claims.

2018

The 2018 water year, that period from Oct. 1, 2017 through Sept. 30, 2018, brought a slew of firsts for rivers and the users who rely on them. Most of those firsts weren’t what anyone would consider good news. The year became Colorado’s second-driest on record, with the searing 2002 drought year barely maintaining its hold on first place. According to the Colorado Climate Center, 16 weather stations that track snow in the mountains recorded a record-low peak snowpack. By the end of the summer, the state’s reservoirs, on average, were less than half full. State officials activated a drought response plan in May covering 34 counties in the

National Integrated Drought Information System (NIDIS) The National Oceanic and Atmospheric Administration’s (NOAA) NIDIS program coordinates drought research and a national drought early warning system. Colorado is part of the Intermountain West drought monitoring program, hosted through NIDIS and the Colorado Climate Center, which evaluates drought on a weekly basis. climate.colostate.edu/~drought and drought.gov Colorado’s Decision Support Systems (CDSS) is a water management system for Colorado’s major river basins provided by the Colorado Water Conservation Board and Colorado Division of Water Resources. colorado.gov/cdss Snow Telemetry (SNOTEL) data is available through the Natural Resources Conservation Service (NRCS) and is part of its Snow Survey and Water Supply Forecasting Program. wcc.nrcs.usda.gov/snow WaterWatch is the U.S. Geological Survey’s (USGS) web interface for water data. waterwatch.usgs.gov C I T I Z E N ’ S G U I D E T O W H E R E Y O U R WAT E R C O M E S F R O M

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Forest Health

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s snowpack accumulates in the mountains, it settles mostly in Rocky Mountain forests.

According to the Colorado State Forest Service, more than 24.4 million acres of native Colorado forestland impact Colorado’s water supply. About 80 percent of the state’s population relies on those forested watersheds for municipal water supplies.

According to the U.S. Forest Service, which manages more than 14.5 million acres of national forest lands in Colorado, 90 percent of those lands are located in watersheds that contribute to public water supplies.

As snowpack melts, runoff eventually collects in small streams that drain toward rivers, creating watersheds and river basins. As water flows down mountain slopes, the forests stabilize soil and prevent erosion, filter contaminants, enhance soil moisture storage and groundwater recharge, and reduce the likelihood of flooding. Due to these valuable ecosystem services, the water running off undisturbed forested watersheds typically has lower nutrient and sediment concentrations compared to flows from urban or agricultural watersheds,

according to the Colorado State Forest Service. But Colorado’s forested source watersheds are still susceptible to damage and contamination that could lead to water impairments. Management of forested lands is therefore a crucial factor in the quality of water available for domestic, agricultural and commercial water uses in Colorado and for downstream states.

While state and federal agencies along with local partners and regional water providers actively manage forest health of Colorado’s source watersheds and protect public water supplies, there is always more work that could be done to mitigate against both natural and humancaused threats. Risks include severe wildfire, insect infestation, and long-term drought. Colorado has seen a growing number of large, high-severity wildfires and never-before-seen levels of tree mortality caused by bark beetle outbreaks over the past two decades. Those natural risks will likely be amplified in the future as a result of climate change. In addition, human-induced factors such as disturbance, roads and pollution also impact forest health and water quality.

offset these impacts. Research on the susceptibility of insect-damaged forests to fire shows that the increasing incidence of fires in Colorado is more closely tied to weather, climate and aridification than to insect infestation, according to the Colorado State Forest Service.

Douglas-fir tussock moth

Wildfires Mountain pine beetle

Emerald ash borer

Insect Infestations Several species of bark beetles—the spruce beetle, Douglas-fir beetle, western balsam bark beetle, fir engraver, and the mountain pine beetle—along with other insects, including the spruce budworm, Douglas-fir tussock moth, and emerald ash borer, have had a massive impact on Colorado’s forests.

Aerial surveys found that the mountain pine beetle alone impacted almost 3.4 million acres in Colorado from 1996 to 2014. While studies have found that the death of these trees may affect snowpack and the timing of runoff, maintaining the remaining live vegetation can help 10 • W A T E R E D U C A T I O N C O L O R A D O

The Colorado Statewide Forest Resource Assessment, published in 2009 by the Colorado State Forest Service, identified 642 priority watersheds susceptible to wildfire damage with a direct link to critical infrastructure for municipal drinking water and 371 forested watersheds with a high or very high risk from post-fire erosion. According to the American Forest Foundation, Colorado has almost 1.4 million acres of public and tribal lands and 636,000 acres of privately owned lands that it classifies as having high fire risk and a high importance to water supply. As temperatures rise, the frequency of wildfires is projected to increase, as is the area burned—a 50 to 200 percent increase in annual area burned is projected by 2050.

While wildfire is natural in undisturbed forest systems, historical fire suppression practices along with an increase in dry, dead trees as a result of insect infestation and a changing climate have increased the severity of fires in Colorado. Severe fires damage forest soils by forming a waterrepelling hydrophobic layer at or below the soil surface. This hydrophobic layer can reduce the infiltration of water into soil. Fires also expose soils to erosion by burning off the vegetation that provides a natural anchor.

A combination of erosion, hydrophobic soils, and ash distribution can result in devastating runoff and mudslides when precipitation falls after a fire. Runoff over burn scars can transport nutrients and pollutants into water supplies and increase the likelihood of flooding and debris flows.

Post-fire runoff and debris flows impact wildlife, fisheries and recreation, as well as infrastructure and drinking water supplies.

These impacts can be seen immediately after a fire and for years to come. According to the Colorado State Forest Service, for more than five years after the 2002 Hayman Fire, stream nitrogen, temperature and turbidity levels remained elevated. Nitrogen WIKIPEDIA AND FORESTRY IMAGES.ORG

The 2002 Hayman Fire left a burn scar that remains today. The fire highlighted the need for source water protection, diverse and redundant water supplies, and forest health and management activities.

and temperature remained elevated for more than 14 years after the fire.

Forest health and management activities such as thinning forests, planting new trees, conducting prescribed burns, and other treatments to reduce fuels can help reduce the severity of fires.

Human Disturbance While undisturbed forest vegetation helps filter water, promote infiltration, MATTHEW STAVER

and protect soil from erosion—all of which reduces sediment yields—human disturbances and management activities such as roads, trails and timber harvesting can contribute sediment to water supplies.

According to the Colorado State Forest Service, these management activities typically have a low impact, increasing erosion rates to between 0.05 and 0.25 tons per acre per year, compared to sediment yields from undisturbed forests, which have been reported at values from 0 to 0.25 tons

per acre annually. Unpaved forest roads are a larger source of sediment-loading in forested watersheds, estimated at 2 to 31 tons per acre in any given year. Increases in recreational trail use and in the number of people residing in the wildland-urban interface likewise pose an increased risk of sedimentation, resulting in diminished water quality. However, forestry bestmanagement practices, such as the establishment of vegetation and streamside buffers, can reduce those effects.

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Infrastructure and Administration

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f necessity is the mother of invention, then mismatch of water supply and water demand may be the mother of Colorado’s complex water system. A vast network of pipes, ditches, treatment plants, laws and treaties divide and distribute the state’s water.

Two basic imbalances help explain Colorado’s physical and legal water infrastructure. The first concerns population: more than 85 percent of Coloradans live on the eastern side of the Continental Divide, while up to 85 percent of the state’s precipitation falls on the western side. The second relates to timing: The majority of Colorado’s water falls as snow during the winter months, while the majority of usage—from agriculture to lawn irrigation— occurs in the summer.

Colorado’s water infrastructure is an attempt to rebalance these discrepancies—to move water from where and when it first falls to where and when it is needed. Colorado’s legal framework governs and allocates the use of and rights to that water.

The Legal Framework The movement and allocation of surface water and tributary groundwater in Colorado is governed largely by the Colorado Doctrine of Prior Appropriation. While all of Colorado’s water is owned by the public, the right to use this scarce resource can be appropriated, bought and sold, subject to review by the state’s water courts.

To appropriate a new water use right, a person, business or public agency must show a concrete plan to put the water to beneficial use by diverting it, storing it, or otherwise capturing and controlling it.

Colorado water law specifies a wide range of beneficial uses, from domestic and agricultural use to oil and gas production to instream flows that protect fish and wildlife and enhance recreation. In times of short supply, court-decreed water rights with earlier dates can be exercised before court-decreed rights with later dates, hence the importance of “prior appropriation.” A decree issued by a water court governs the use of every water right and specifies a right’s priority date, source and place of diversion, along with its time, type and amount of use. Importantly, it also contains conditions to ensure that the use of one water right does not result in injury to others.

When the prior appropriation doctrine became part of Colorado’s constitution in 1876, it was a break from the so-called “riparian doctrine of reasonable use” 12 • W A T E R E D U C A T I O N C O L O R A D O

that predominates the eastern half of the United States, where typically only those with land adjoining the stream or overlying the aquifer have the right to use that water. Under Colorado’s system, anyone can acquire and operate a right to use the state’s waters, so long as they refrain from injuring other water rights, don’t waste the water, and continue putting their water to beneficial use. Rights that are not put to beneficial use for a period of 10 years or more risk being investigated for abandonment (see WEco’s Citizen’s Guide to Colorado Water Law).

Colorado can consume only about one third of the runoff that originates within its borders, thanks to a long list of interstate and international agreements. Nine interstate compacts, two U.S. Supreme Court equitable apportionment decrees, and two other agreements with other states govern how much water Colorado is able to consume within its boundaries.

The most well known of these is the Colorado River Compact of 1922. It requires the upper Colorado River Basin states of Colorado, New Mexico, Utah and Wyoming to allow a rolling average of 75 million acre-feet of water over a 10-year period to flow to the lower Colorado River Basin states of Arizona, Nevada and California. More than 40 million people throughout the basin depend on the Colorado River.

Separate compacts and decrees also govern water sharing between Colorado and the states of Kansas, Nebraska,

New Mexico, Texas and Wyoming, with water flowing from those states farther downstream (see WEco’s Citizen’s Guide to Colorado’s Interstate Compacts).

Transbasin Diversions There are 44 diversions in the state that together move more than 1.6 million acrefeet of water each year from native river basins to receiving basins. Of these, 27 are considered transbasin diversions, bringing a combined average of 580,000 acre-feet of water annually from one of Colorado’s four major river basins—the Arkansas, Colorado, Platte and Rio Grande—to another, with one, the San Juan-Chama Project, crossing state lines (see WEco’s Citizen’s Guide to Colorado’s Transbasin Diversions).

Each is a feat of engineering, a complex and even audacious network of tunnels, pumps, pipelines and ditches. And each transbasin diversion meets the water supply needs of water users, demonstrating the impact of moving water from its source to its place of use, which in many cases is hundreds of miles away.

Many of the state’s transbasin diversions were built between the 1930s and 1960s, with an infusion of federal money from the Public Works Administration and the U.S. Bureau of Reclamation in the wake of the Great Depression. Over time, they have shaped development patterns along Colorado’s Front Range and have become a lynchpin of the state’s economy. Some, like Denver’s water system, were built without federal aid. Transbasin diversion water represents roughly half of Denver’s water supply, and highly productive agricultural operations in places like the South Platte and the Arkansas River basins are substantially dependent on transbasin diversions like the Colorado-Big Thompson Project and the Fryingpan-Arkansas Project.

Despite their tremendous economic value, transbasin diversions have taken an environmental toll in headwaters communities just west of the Continental Divide and all of the way to the Utah border, where they have reduced streamflows, threatening water quality, aquatic health, wildlife habitat, and recreational opportunities. Recognizing these

Twin Lakes Reservoir, located 13 miles south of Leadville, is part of the Fryingpan-Arkansas Project, a transbasin diversion that moves water from the Fryingpan and Roaring Fork rivers and their tributaries to the Arkansas River Basin. Water from Twin Lakes is delivered into the Arkansas River and reaches as far as Sugar City in southeastern Colorado, 220 miles downstream.

realities, supporters of new or expanded transbasin diversion projects have begun to work more closely with headwaters communities in recent years to mitigate their impacts. One notable example is the Colorado River Cooperative Agreement, signed by Denver Water and 40 West Slope entities in 2013.

RICHARD STENZEL

Moving and Storing Water Aside from moving water across the Continental Divide via transbasin diversions, the public water utilities that serve most Coloradans also collect, store, treat and distribute water supplies through a vast network of water infrastructure.

Utilities use pipes, valves and pumps to move water from rivers, streams and aquifers into tanks, reservoirs or other storage facilities. Aquifers themselves can even serve as a form of underground reservoir through aquifer storage and recovery (ASR) projects.

Reservoirs are man-made bodies of

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â&#x20AC;˘

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Colorado’s Transbasin Diversions Identified by the arrows on the map, 44 diversions move water from one of Colorado’s major watersheds to another. Of those, 27 are considered transbasin diversions, in that the water they transport crosses between two of the state’s four major river basins: the Colorado, the Platte, the Arkansas, and the Rio Grande.

STEAMBOAT SPRINGS

WALDEN N. PLATTE

FORT COLLINS GREELEY ESTES PARK

YAMPA / WHITE

WINTER PARK

BOULDER

SOUTH PLATTE / REPUBLICAN

DENVER AURORA

VAIL COLORADO

GRAND JUNCTION

ASPEN

DELTA

COLORADO SPRINGS

GUNNISON

MONTROSE PUEBLO

ARKANSAS

CONTINENTAL DIVIDE

LA JUNTA RIO GRANDE

DOLORES / SAN JUAN

ALAMOSA

DURANGO

SOURCE: Colorado Division of Water Resources

water held in place by dams, some of which generate electricity using turbines that spin as water is released to move downstream or through their delivery system. Aside from storing water, some reservoirs also regulate river flows—by reducing reservoir releases to prevent rivers from cresting their banks and flooding.

Reservoir water is used to supply everything from municipal and industrial purposes to agricultural irrigation, fish and wildlife habitat, and the satisfaction of interstate water delivery requirements.

As of 2019, Colorado had 1,953 reservoirs with a total storage capacity of about 7.5 million acre-feet. Due in part to the major cost of building new reservoirs, many were constructed by the federal government.

More than half of Colorado’s reservoir 14 • W A T E R E D U C A T I O N C O L O R A D O

water is stored in 113 federally owned reservoirs throughout the state, according to the Colorado Water Plan.

In addition to reservoirs, aquifers can also be used to store water through a process called aquifer storage and recovery or ASR. ASR is the injection of water into an aquifer for later recovery and use. Development of ASR facilities in the U.S. has been on a rapid growth curve for the past 20 years, with 125 wellfields now established in over 20 states. As of November 2016, Colorado had 6 different operating wellfields consisting of 45 ASR wells. To date, no ASR projects exist outside of the Denver Basin, however since 2017, with the passage of HB17-1076, the State Engineer’s extraction rules apply to nontributary aquifers throughout the state.

Municipal Treatment and Delivery Systems Municipal water accounts for 7 percent of consumptive water use in Colorado and 6.7 percent of water diversions. After it is diverted from its source and possibly stored in a reservoir, municipal water is sent to treatment plants, where it is treated in accordance with regulations like the federal Safe Drinking Water Act. The Colorado Department of Public Health and Environment’s Water Quality Control Division monitors and enforces public water systems’ compliance with regulatory requirements (see WEco’s Citizen’s Guide to Colorado Water Quality Protection).

Different drinking water treatment and water purification plants use different CHAS CHAMBERLIN

BLUE MESA

GRANBYMCPHEE RESERVOIRPUEBLO

DILLON

JOHN MARTIN GREEN MOUNTAIN HORSETOOTH VALLECITO SUGARLOAF

Horsetooth Reservoir, just west of Fort Collins, is part of Northern Water’s Colorado-Big Thompson Project system. The water in the reservoir is sourced primarily from the Colorado River headwaters on the West Slope and is used by cities, small domestic water suppliers, industries, and farms and ranches in eight counties of northeastern Colorado.

treatment systems, depending on the quality of the raw water that enters their plant.

Typically, drinking water treatment begins with coagulation and flocculation. During this step, chemical compounds called coagulants are added to the water. They attract solids to create larger particles called floc. The floc then settles to the bottom of the treatment tank through a process called sedimentation. Clarified water is then passed through filters—often fine sand or charcoal filters—before being treated with a disinfectant like chlorine or chloramine.

From the treatment plant, clean water is pumped into the utility’s distribution system, a network of pipes and pump stations that brings water to the meters at individual homes and businesses. The high cost of building, maintaining and repairing ADOBE STOCK; COLORADO DIVISION OF WATER RESOURCES

Colorado’s 10 Largest Reservoirs Although there are close to 2,000 reservoirs in Colorado, the 10 largest have a combined normal storage capacity of 3,272,088 acre-feet, comprising more than 40 percent of the state’s total storage. Nine of these reservoirs are federally owned. More than half of the state’s reservoir water is stored in federally owned reservoirs.

In thousands of acre-feet 1,000

940.8 800

600

539.8

400

381.1

357.7 254.0

200

232.9

154.6

152.0

0

Blue Mesa

Granby

McPhee

Pueblo

Dillon

John Martin

Green Horsetooth Mountain

129.7

129.4

Vallecito Turquoise

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water treatment plants, distribution pipes and wastewater systems accounts for most of the average water bill, and—along with increasing competition for water supplies— is a major reason that water rates in most communities continue to rise.

The customer’s plumbing system represents the privately owned part of the water supply system. People are familiar with plumbing systems because they use them daily, but they are only the final link in a very long chain of facilities that delivers water to the tap where it can finally be used.

Most of the water that flows through indoor taps returns to the system as wastewater. After use, municipal and industrial wastewater, also known as indoor return flows, flows into a sewage system where it is routed—via gravity or with the help of pumps—to a wastewater treatment plant for treatment in accordance with federal and state water quality control laws, guided by the Clean Water Act. In the primary stage of wastewater treatment, solids settle out or are removed from wastewater using screens and scrapers. In the secondary stage, wastewater flows into aeration tanks where bacteria consume organic waste. Additional treatment steps such as filtration or more biological treatment to remove phosphorus, nitrogen compounds, toxic substances or other pollutants may be completed.

Typically, water is then pushed through fine filters and subjected to ultraviolet light to disinfect it, before being reintroduced into local bodies of water and sent downstream for other communities to use.

Return Flow Return flow is surface water or groundwater that returns back to rivers or shallow aquifers after being applied to beneficial use. In most irrigation systems, crops consume a portion of the water applied and unused water becomes a return flow.

In many places in Colorado, return flows make their way back to the river only to be diverted and return to the river again before finally exiting the state. Downstream water users depend on these return flows to fulfill their water rights. For this reason, when an agricultural water right is sold and transferred to another beneficial use, the future consumption of that water is limited to the beneficial historical consumptive use of the original water right—the return flow volume and timing patterns must be accounted for in order to prevent injury to downstream water users.

In this example, an agricultural diversion takes 10 cubic-feet-per-second, diverting half of a river’s flow.

The irrigator applies all that water to her crop, but the crop consumes only 60 percent. The remaining 40 percent of that water will eventually make its way back to the river and can be diverted and used by downstream water users—assuming it is not lost to evaporation, is not intercepted by phreatophytes and other water-loving plants, and does not infiltrate into an aquifer.

RIVER

20 cfs

H TC

DI

Diversion of 10 cfs 1,000 acre-feet applied to field

6 cfs 600 acre-feet consumed by crop

10 cfs

Return flow: 4 cfs 400 acre-feet returns to the river by surface or groundwater

SOURCE: Colorado Division of Water Resources

Agricultural Diversion Systems Agriculture accounts for more than 80 percent of Colorado’s consumptive water use and more than 86 percent of Colorado’s surface water diversions. Farmers and ranchers divert surface water from rivers and streams using headgates, which are mechanical diversion structures that can be adjusted to alter how much water is allowed through. Headgates direct water into large ditches or canals. From those canals, smaller ditches or pipelines branch off to supply individual farms and fields. These delivery systems are often owned and managed by agricultural water districts or ditch 16 • W A T E R E D U C A T I O N C O L O R A D O

companies, which often also own water rights and, in some cases, construct storage.

Many farmers, in turn, own ditch company shares granting them specific quantities of water each year. Ditch company members also pay assessment fees to maintain the ditch system and compensate a ditch rider, who repairs and patrols the system to ensure that shareholders get their water entitlements.

Many of Colorado’s agricultural ditches are earthen, so some water is lost in transit as it seeps into the ground. This water can be consumed by nearby vegetation but also makes its way into tributary groundwater

14 cfs

aquifers, which are hydrologically connected to surface streams. In this way, it is possible for seepage from canals and ditches to return to the river. Some farmers line or pipe their ditches to decrease these delivery losses. While lined ditches make for more efficient delivery systems and less water loss, they can alter wildlife habitat previously supported by ditch seepage and can reduce flows to the river or to aquifers pumped by groundwater wells, which other farmers may have come to rely on to exercise their water rights.

Agricultural water that is permanently taken up and used by growing crops via CHAS CHAMBERLIN

An agricultural ditch off the South Platte River winds through fields near Sterling, Colorado.

MATTHEW STAVER

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evapotranspiration is called “consumptive use” water. This is the water that farmers and ranchers can claim when they go to water court to sell or change their water rights to a new use. Consumptive use is scientifically determined by crop type and acreage, and is dependent on characteristics like the crop’s growing season, water requirements for each stage of crop development, soil texture, and evapotranspiration rate.

Typically, water applied to a farmer’s field is not entirely consumed by plants.

Rather, some water conveyed to the field is not consumed and ultimately returns to the river or aquifer as return flows. Downstream farmers often rely on return flows to meet their water needs. Water users in many of Colorado’s river basins are heavily dependent on return flows: The South Platte Basin, for instance, has a flow of about 2 million acre-feet annually, but more than 4 million acre-feet of water is diverted there each year, indicating that much of the basin’s water is diverted and reused more than once before it leaves the state.

Groundwater Wells Roughly 11 percent of Colorado’s population, about 591,000 residents, relies on groundwater for its water supply. The infrastructure they depend on looks very different from a typical municipal water system. Well owners can drill wells into either tributary groundwater aquifers— which have subterranean connections to nearby rivers and streams—or nontributary aquifers, which are located deeper in the earth and separated from surface water by layers of rock. All water wells require a permit from the State Engineer to drill and operate the well.

Because of the connection between tributary groundwater and surface water, well pumping can have an impact on nearby streams. Therefore, there’s a legal obligation that requires many well owners obtain approval of a plan to mitigate impacts to the river caused by their well pumping. Such plans are called augmentation plans and may use leased water or purchased water rights to mitigate those impacts through direct delivery to the stream, released reservoir water, or accretions to the stream 18 • W A T E R E D U C A T I O N C O L O R A D O

from delivery to recharge ponds at the time, place and amount that it would have arrived in the absence of pumping their well.

In addition to tributary and nontributary groundwater, Colorado also has designated groundwater. The Colorado Ground Water Commission regulates use of designated groundwater in Colorado’s Eastern Plains. Like tributary and nontributary groundwater, drilling wells into designated groundwater formations also requires a permit from the State Engineer. Instead of being administered according to the prior appropriation system, pumping of designated groundwater is administered according to a modified prior appropriation system and may require a replacement plan to replace depletions if groundwater well pumping impacts other wells.

Water Reuse Not all water comes straight from a river or well. One way to reduce dependence on supplies of fresh water is to reuse water.

Various forms of reuse are now in place across Colorado, and the practice is expected to become more common as population growth and climate change strain the state’s water supplies in the coming decades.

Some forms of water—such as transbasin diversion water, consumptive use water derived from permanent transfers of agricultural water rights to urban uses, and nontributary groundwater whose pumping does not affect surface water supplies—can legally be reused to extinction, and thus are particularly well suited for reuse projects.

The most basic form of reuse has occurred for as long as communities have drawn water from a single river basin.

When one community discharges treated wastewater and that water is picked up by a community downstream, treated again and put to municipal use, a straightforward form of de facto reuse has occurred. Yet reuse can occur on many scales, from the recycling of an entire community’s water to the repurposing of wastewater from a single household.

Graywater recycling, defined as the collection of wastewater from sources like showers, bathtubs, bathroom sinks, and laundry machines, or any source other than toilets and urinals, kitchen sinks,

dishwashers and non-laundry utility sinks, is one household-scale example. Through creative plumbing, some homes use graywater from sinks to fill and flush their toilets or irrigate their outdoor plants.

On the city-wide scale, non-potable water reuse projects redirect purified wastewater for purposes like park and golf course irrigation. The cities of Colorado Springs and Denver both have long standing nonpotable reuse programs using such water for city parks and power plants.

Several water utilities in Colorado have also implemented indirect potable reuse projects, where wastewater is treated, discharged into surface or subsurface water supplies, then reclaimed downstream and treated to meet drinking water standards. Aurora’s Prairie Waters Project is one example: Using downstream wells, the utility captures reusable transbasin diversion water that has been discharged from the Metro Wastewater Reclamation District treatment plant into the South Platte River. That water undergoes natural “riverbank filtration” before it is pumped many miles south to the Binney Water Purification Facility. After treatment, some of the water is reused by Aurora while the rest is piped to 10 water provider members south of Denver as part of a water-sharing agreement. When fully utilized, Aurora Water officials estimate that Prairie Waters will provide up to 50 million gallons of water a day to people in the Denver metro area.

Direct potable reuse, where wastewater is treated and then piped directly back to consumers as potable water, is the least developed form of reuse in Colorado.

Numerous pilot projects have demonstrated that the technique is feasible, but regulators have yet to develop rules to monitor and regulate the protection of public safety.

Resiliency Whether it relies on reuse, the diversion of surface water, or a simple groundwater well, every water system is somewhat vulnerable to natural and man-made disasters like wildfires, droughts, floods and chemical contamination. That is why it’s vital for municipal water providers to have backup water supplies.

Stretching Supplies with Water Reuse Here, a hypothetical community with 1 acre-foot of water uses 0.4 acre-feet outdoors and 0.6 acre-feet indoors. With no reuse, the community gets 1 acre-foot of use from the water, though indoor return flows are treated, return to the stream and can be diverted by downstream water users. With additional treatment and recycling, indoor return flows can be recaptured and stretched within the

community. Through non-potable reuse, 1 acre-foot of legally reusable water multiplies to 1.5 acre-feet of reuse water. With indirect and direct potable reuse, 1 acre-foot of water can be nearly doubled to 1.9 acre-feet, as indoor return flows are reused multiple times, assuming 10 percent treatment and transit loss in each cycle.

No Reuse Total use in community 1 acre-foot

LEGALLY REUSABLE WATER

FLOWS DOWNSTREAM FOR DE FACTO REUSE

DRINKING WATER TREATMENT PLANT

CONSUMERS RETURN FLOWS FROM INDOOR USE

1 acre-foot intial supply

WASTEWATER TREATMENT PLANT

DISCHARGED TO STREAM

Nonpotable Reuse Total use in community 1.5 acre-foot

LEGALLY REUSABLE WATER

DRINKING WATER TREATMENT PLANT

CONSUMERS RETURN FLOWS FROM INDOOR USE

1 acre-foot intial supply

WASTEWATER TREATMENT PLANT

RECLAIMED WATER TREATMENT FACILITY

NONPOTABLE REUSE —GOLF COURSES, PARKS, ETC. 0.5 acre-foot reuse supply

Potable Reuse Total use in community 1.9 acre-foot Available supply in acre-feet 1.0

LEGALLY REUSABLE WATER

DRINKING WATER TREATMENT PLANT

0.5

0.25 0.13

WASTEWATER TREATMENT PLANT

CONSUMERS

RETURN FLOWS FROM INDOOR USE

THIRD REUSE

ADVANCED WATER TREATMENT FACILITY

SECOND REUSE

FIRST REUSE DIRECT REUSE

ENVIRONMENTAL BUFFER OPTIONAL INDIRECT REUSE

SOURCE: Western Resource Advocates

CHAS CHAMBERLIN

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Colorado’s River Basins

C

olorado is the headwaters state for much of the western and central United States: Most of its rivers begin in the Rocky Mountains and flow across state lines. Four of the nation’s major rivers originate in Colorado: the Arkansas, Colorado, Platte, and the Rio Grande. Only the Green River, the Little Snake River, and Costilla Creek flow into the state, and then only for short stretches. Rivers are the predominant water source for Coloradans. This water is highly prized because it starts as pristine high-quality snowmelt, not yet used and reused by others. Other states are not so fortunate.

Within Colorado, major river basins include the Arkansas, Colorado, Gunnison, North Platte, Republican, Rio Grande, South Platte, Dolores/San Juan/San Miguel, and the Yampa/White/Green. Those basins are grouped differently for the Colorado Water Conservation Board’s roundtable processes and for the purpose of water administration by the Division of Water Resources.

Each basin relies on a mixture of rain, snow and groundwater to fill its rivers and creeks and each basin hosts a distinct range of water uses that help shape Colorado’s overall identity.

Through this section, we survey Colorado’s river basins, where the water flows from the headwaters to the state line, and how the water is stored and used.

Gunnison River Basin The Gunnison River begins high in the mountains of central Colorado and flows west, stretching across more than 8,000 square miles of western Colorado, from the Continental Divide to its confluence with the Colorado River near Grand Junction.

After this confluence, the volume of the Colorado River is almost doubled by the Gunnison River.

According to the Colorado Water Plan, forest area covers more than 50 percent of the basin, and about 5.5 percent of the land in the basin is planted, supporting a vibrant mix of farms, vineyards, orchards and ranches.

The Gunnison Basin contains the largest reservoir in the state, Blue Mesa Reservoir, completed in 1965 with a 940,800 acre-foot water storage capacity, according to the Colorado Division of Water Resources.

Other major reservoirs in the basin include Morrow Point Reservoir, Taylor Park Reservoir, and Ridgway Reservoir. Only small quantities of water are imported to the basin, but a number of transbasin diversions move water out of the basin. Through the Redlands Canal or Redlands Diversion Dam, each year about 500,000 acre-feet of water is diverted from the Gunnison River close 20 • W A T E R E D U C A T I O N C O L O R A D O

to its confluence with the Colorado River near Grand Junction. That water is used for power generation and for irrigation in the Grand Valley.

Colorado River Basin It is hardly a stretch to call the Colorado River the lifeblood of the American Southwest. Flowing from the Continental Divide to the Gulf of Mexico, the Colorado provides water to more than 40 million people in seven U.S. states and Mexico.

Less than 20 percent of the entire Colorado River Basin lies inside Colorado, but about 75 percent of the water that feeds the river originates here, according to the Colorado Water Plan. The Colorado River Compact of 1922 divides the waters of the Colorado among the basin states for the people who rely on its waters.

Within Colorado, the basin encompasses about 9,830 square miles. Rangeland and forests are predominant landscapes in the basin, comprising about 85 percent of the area. Elevations in the basin range from more than 14,000 feet near the headwaters to about 4,300 feet at the Colorado-Utah state line.

In Western Slope headwaters communities, the Colorado River supports fishing, rafting, ski area snowmaking, and

wildlife habitat. As it flows west, it supports livestock grazing, timber harvesting, oil and gas drilling, the orchards and vineyards of Palisade, the wheat and alfalfa fields of the Grand Valley, the citizens of Grand Junction and other towns, as well as fish and wildlife populations.

Snowpack in high elevations is an important water source on both sides of the Continental Divide. Transbasin diversions reroute a large fraction of this water, between 450,000 and 600,000 acre-feet annually, from the headwaters of the Colorado. Much of that water goes to Colorado’s Eastern Slope, where it makes up roughly half of Denver’s water supply and serves many other cities and farms on the Front Range. The largest transbasin diversions include the Adams Tunnel which is a principal component of the Colorado-Big Thompson Project and carries an average of 216,570 acre-feet annually from the Colorado to the South Platte Basin; as well as the Roberts Tunnel, Moffat Tunnel and Boustead Tunnel, which are each responsible for 50,00060,000 acre-feet of water diverted out of the Colorado Basin each year. The largest storage project in the basin is Granby Reservoir, which is part of the ColoradoBig Thompson Project and is the second largest body of water in the state.

Yampa/White/Green River Basin The Yampa River, White River, and Green River basins cover about 10,500 square miles in northwest Colorado and south-central Wyoming. Elevations in the basin range from 12,200 feet to about 5,100 feet at the confluence of the Yampa and Green Rivers at Echo Park in Dinosaur National Monument.

The Yampa is known as the last major “wild” or free-flowing tributary throughout the entire seven-state Colorado River Basin, due to its predominantly undammed status and natural hydrograph—the timing and variation of its flows over the course of the year. The Yampa flows into the Green in Colorado before the Green River reaches the Colorado River in Utah. While it’s considered wild, there are some reservoirs in the basin. Stagecoach Reservoir is the largest, with a capacity of 33,275 acre-feet.

Colorado Wet and Dry Year Streamflows Colorado is a headwaters state. This map shows typical annual high and low streamflows measured in acre-feet at gauges along Colorado’s major rivers and tributaries, and as flows leave the state. This map was originally published in the Colorado Water Plan in 2015 by the Colorado Water Conservation Board and modified

by Water Education Colorado.

9,100

457,000

Rive

r !

A

572,000

1,050,000 !

A 478,000

107,000 68,000

!

A

49,000 24,000 191,000 62,000

6,853,000

eR

11,226,000 ,226,000

!

A

880,000 169,000

30,000 19,000

!

A

!

A

Glenwood ! ! A Springs A !

1,222,000 A COLORADO 595,000

latt

Greeley

!

8,000 !

A !

A A

SOUTH PLATTE

577,000 577

63,000 42,000 170,000 !

A 108,000

446,000

!

A 206,000

!

A

iver

278,000 170,000 86,000 !

A 56,000

NORTH PLATTE

!

A

YAMPA

hite

!

A

!

A

873,000 139,000 !

A

th P

561,000 !

A 211,000 A 2,265,000 ! !

A 896,000 712,000 350,000 W

Steamboat Springs

Sou

1,566,000 670,000 Yampaa River

!

A

!

A 3,300

!

A 152,000

!

A 251,000 51

2,400 18,000 4,000

Denver

!

A !

A

!

A 2,842,000 !

A

2,876,000 1,043,000

2,342,000

Colorado Springs

!

A

Dolore s Rive

1,374,000 1 37 1,37

r

!

Montrose A

455,000 000 ! ! 431,000 A 56,000 A

273,000

!

A 120,000

730,000 351,000

733,000 !

A 367,000

174,000 74,000

GUNNISON

250,000 133,000

CONTINENTAL DIVIDE

!

A

SOUTHWEST

!

A

204,000 !

92,000 A

461,000

52,000 !

A 35,000

Durango 41, 41,000 1,000 !

A 12,000

!

A

Gages

xxx xxx

!

A

309,000 89,000 447,000 181,000 !

A 690,000 ! !

A A 259,000

AFY (typical wet year) AFY (typical dry year)

Streams

The basin contains steep mountain slopes, high plateaus, canyons, alluvial valleys and floodplains. Agriculture—primarily livestock and grazing—accounts for the vast majority of water use in the basin. Much land in the Yampa River Basin is federally owned, which supports a thriving tourism industry featuring sports like rafting, tubing, kayaking, fishing and skiing. Livestock grazing and recreation are the predominant land uses in the basin. Species such as the federally protected Colorado pikeminnow also depend on the Yampa’s flows.

Two coal-fired power plants have been the basin’s main industrial water users, but one, Xcel Energy’s Hayden Station,

COLORADO WATER CONSERVATION BOARD

ARKANSAS

Arkansas s River

!!

A A

131,000 !

A Pueblo

RIO GRANDE

42,000

!

A 23,000 !

18,000 A

9,900

860,000 438,000

318,000 103,000

!

A !

A

57,000 39,000

155,000 61,000 !

A

250,000 115,000

!

A

!

A

Alamosa

!

A

178 178,000

!

A 33 33,000

50 501,000

!

A 167,000

Typical Wet Year Flow Typical Dry Year Flow

Major Hydrologic Basins in Colorado

is set to retire completely by 2036. At the other power plant, Craig Station, Unit 1 is expected to retire in 2025 and, according to Xcel’s Electric Resource Plan, Unit 2 will retire by 2039.

North Platte River Basin The North Platte River Basin encompasses about 2,000 square miles of north-central Colorado, and consists of a broad valley ringed by three mountain ranges: the Medicine Bow Range to the east, the Park Range to the west, and the Rabbit Ears Range to the south. The basin includes Jackson County and the small portion of

NOTE: Wet and dry typical hydrology years determined separately for each basin.

Larimer County that contains the Laramie River watershed, though the Laramie River does not reach the North Platte until the two rivers meet in Wyoming. Both rivers are subject to use limitations stemming from Supreme Court equitable apportionment decrees. These legal protections prevent the depletion of the North Platte River, leaving those already diverting water for agricultural or municipal use with a finite supply.

In addition to the U.S. Supreme Court decrees, the North Platte is party to the Three State Agreement of the Platte River Recovery Implementation Program between Colorado, Wyoming and Nebraska, which guides water use in the basin and is intended to aid the

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recovery of endangered species in Nebraska, including three birds—the whooping crane, least tern and piping plover—and a fish, the pallid sturgeon, through work with the U.S. Fish and Wildlife Service. This agreement applies to consumptive water use in the North Platte Basin of 134,467 irrigated acres.

The economy of the North Platte Basin is dominated by irrigated ranching operations.

More than 400 irrigation ditches divert water from the North Platte and its tributary streams. The basin also hosts a wide range of seasonal recreation like fishing, backpacking, hunting and snowmobiling and contains a major wildlife refuge in addition to a variety of public lands.

The population center of the basin is the Town of Walden in Jackson County, with a population estimated to be just under 600 people according to the Colorado Department of Local Affairs. The North Platte is unique within Colorado: It is the only basin that does not foresee a gap between supply and demand for municipal uses in the future. However, water is exported from the basin—the largest

diversion, the Laramie-Poudre Tunnel, diverts around 15,000 acre-feet of water each year from the Big Laramie River in the North Platte Basin to the South Platte Basin.

South Platte River Basin The South Platte River originates in the mountains of the northern Front Range, then flows northeast through Denver before crossing the High Plains into Nebraska near Julesburg. In Nebraska, the South Platte merges with the North Platte River to form the Platte River. About one-third of the basin’s land area is publicly owned and is primarily forested lands in the western mountainous part of the basin. The eastern, High Plains region of the basin is mainly grassland or cultivated land.

According to the Colorado Water Plan, more than 85 percent of Colorado’s population resides in the South Platte Basin, and the Front Range is a center for sectors like tech, aerospace and energy, along with widely publicized industries like craft beer.

The South Platte Basin also has the greatest

Reservoirs along Colorado’s rivers allow for controlled and regulated flows for much of the year. When there are high flows, reservoirs capture that flow to use later and to prevent flooding. When river flows decline, water can be released from storage to meet human and environmental needs. But with that control comes the loss of the natural hydrograph. On the Yampa, considered one of the wildest rivers in the West, a more natural hydrograph shows flows building as snowmelt begins in the spring, peaking in early summer, and dipping to their

concentration of irrigated agricultural lands in Colorado and the highest agricultural production of any of the state’s river basins.

The basin also supports water-dependent ecological and recreational attributes including skiing, boating, fishing, and wildlife viewing and hunting.

The basin’s water supply is highly dependent on both transbasin diversions and return flows. Along with a native flow of about 1.4 million acre-feet per year from precipitation—most of it beginning as snowpack in the northern Colorado Rockies—the river benefits from another 400,000 acre-feet of transbasin diversions from the Colorado River and roughly 100,000 acre-feet from the Arkansas, North Platte, and Laramie river basins.

Taken together, these sources result in an annual flow of just less than 2 million acre-feet, supplemented by about 30,000 acre-feet of well pumping from nontributary groundwater aquifers. And yet, annual surface water diversions in the basin are roughly 4 million acre-feet, suggesting that much of the basin’s water

lowest in late summer. The gauge near Maybell, downstream of Stagecoach Reservoir, Steamboat Springs, and Craig, is the last gauge before the river’s confluence with the White. On the South Platte in Commerce City, downstream of Denver and just upstream of the effluent outfall from the Metro Wastewater Reclamation District, that natural bell curve is eliminated but water is available when needed, with high flows throughout the irrigation season, into fall.

Discharge, in cubic feet per second 8,000

1,000

Yampa River near Maybell

South Platte at 64th Ave., Commerce City 0 Nov. 1 2017

22 • W A T E R E D U C A T I O N C O L O R A D O

Jan. 1 2018

Mar. 1 2018

May 1 2018

July 1 2018

Sept. 1 2018

U.S. GEOLOGICAL SURVEY

is used more than once. Many water users depend on return flows from cities and farms upstream. They also rely on storage reservoirs throughout the basin.

The largest reservoirs are Horsetooth and Carter Lake in Larimer County.

The 1923 South Platte River Compact establishes Colorado’s and Nebraska’s rights to use South Platte River water.

The Platte River Recovery Implementation Program is a stakeholderdriven program that provides Endangered Species Act compliance in the Platte for Colorado, Wyoming and Nebraska, through work with the U.S. Fish and Wildlife Service. Without the regulatory certainty provided by this program, water users in the South Platte Basin would be subject to arduous requirements and possible reductions in water use to ensure continued protection of endangered species.

While stakeholders in the South Platte Basin face a number of challenges in the coming years, one of the most significant will be securing a reliable water supply for a rapidly growing population while protecting agriculture, the environment and recreation.

According to the 2019 Analysis and Technical Update to the Colorado Water Plan, the basin’s population is projected to grow from about 3.8 million people in 2015 to between 5.4 and 6.5 million people by 2050.

Republican River Basin Located on Colorado’s northeastern High Plains, the Republican River is 430 miles long and flows west to east. The basin is formed by the confluence of the North Fork of the Republican River and the Arikaree River just north of Haigler, Nebraska.

The South Fork joins just southeast of Benkelman, Nebraska. Because the river is fed by local precipitation and groundwater rather than snowmelt from the Rockies, it does not run year-round in some locations.

The landscape of the basin is comprised mainly of grassland and cultivated land, with agriculture as the dominant water use. Yuma, Kit Carson, Phillips and Washington counties are ranked in the top 10 agricultural producing counties in Colorado. As of 2014, the basin was home to about 560,000 irrigated agricultural acres, or one-fifth of the state’s total. Most of this WATER EDUCATION COLORADO

CONTINENTAL DIVIDE

STEAMBOAT SPRINGS

WALDEN N. PLATTE

FORT COLLINS GREELEY

ESTES PARK

YAMPA / WHITE

WINTER PARK

BOULDER

SOUTH PLATTE

REPUBLICAN

DENVER AURORA

VAIL COLORADO

GRAND JUNCTION

ASPEN

DELTA

COLORADO SPRINGS

GUNNISON

MONTROSE PUEBLO

ARKANSAS

LA JUNTA RIO GRANDE

ALAMOSA

DOLORES / SAN JUAN / MIGUEL

DURANGO

The Republican River Basin rises from the High Plains in eastern Colorado as the river flows into Nebraska.

For the purposes of the Colorado Water Conservation Board’s water supply planning work, the Republican is grouped in with the South Platte Basin; for the Division of Water Resources administration work, the Republican is part of Division 1, along with the South Platte.

acreage is irrigated by groundwater pumped from the Ogallala Aquifer. The larger Colorado municipalities within the basin include Wray, Yuma and Burlington.

The Colorado Ground Water Commission regulates water in Colorado pumped from the Ogallala Aquifer, a vast underground reservoir that is being unsustainably depleted. The Ogallala stretches from South Dakota to New Mexico and Texas and along Colorado’s eastern border.

The 1942 Republican River Compact divides the waters of the Republican between Colorado, Kansas and Nebraska.

However, groundwater pumping has caused disputes and litigation among the basin states. In response, the state legislature created the Republican River Water Conservation District in 2004 which is working in various ways to increase streamflows and offset stream depletions to comply with Colorado’s compact obligations.

Arkansas River Basin The Arkansas River Basin covers a huge territory, more than 28,000 square miles, encompassing more than a fifth of Colorado’s total land area. The Arkansas

River flows from its headwaters near Leadville through the Front Range cities of Cañon City and Pueblo before unspooling onto the Eastern Plains and crossing into Kansas near the town of Holly.

In the upper basin, uses like trout fishing and whitewater rafting dominate—Browns Canyon National Monument between Buena Vista and Salida is among the most popular whitewater rafting destinations in the country.

The Lower Arkansas River is a water source for towns and cities like Pueblo and Colorado Springs, though they rely primarily on transbasin diversion water, brought over through the Fryingpan-Arkansas Project and conveyed through the Arkansas River.

The river also supports a longstanding Eastern Plains agricultural economy.

Grassland covers about 67 percent of the basin, and a large amount of that is devoted to agriculture, with one-third of agricultural lands requiring irrigation. Major water storage projects in the basin include John Martin Reservoir, Pueblo Reservoir, Great Plains Reservoir, and others.

Water use in the Arkansas Basin is constrained by the 1948 Arkansas River Compact between Colorado and Kansas,

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which prevents Coloradans from depleting the river’s flow at the Kansas border below 1948 levels. This restriction prompted Colorado to adopt new rules in 2011, mandating that any farmers that increase their consumptive use of water by adopting more efficient irrigation technology must purchase augmentation water and return it to the river, to ensure that the timing and amount of return flows to the Arkansas remains unchanged.

Rio Grande Basin Located in south-central Colorado, the headwaters of the Rio Grande Basin is defined by the San Juan Mountains to the west, the Sangre de Cristo and Culebra Mountains to the east, the La Garita Mountains to the north, and the ColoradoNew Mexico state line to the south.

Between the San Juan Mountains and the Sangre de Cristo Mountains lies the San Luis Valley, which has an average elevation of 7,500 feet and precipitation of less than eight inches per year. That makes it the driest part of the state. The basin covers more than 7,500 square miles.

More than 600,000 acres of irrigated land in the San Luis Valley is used for agricultural purposes. Producers in the valley are the second largest provider of fresh potatoes in the United States (behind the well-known Idaho potatoes). Barley and alfalfa are other major crops. Non-irrigated areas in the valley are mostly classified as shrubland (24 percent) and grassland (31 percent).

Because the Rio Grande Basin receives such little precipitation, groundwater pumped from the confined and unconfined aquifers beneath the San Luis Valley is critical for agriculture. However, long-term drought and over-use have led to the decline of these aquifers and state rules now require the replacement of well-pumping depletions. Farmers have responded with an innovative program to replenish the aquifer, where subdistricts of the Rio Grande Water Conservation District assess fees on groundwater withdrawals and the proceeds are used to pay farmers to fallow some of their land.

Alamosa is the largest city in the basin and has a population just shy of 10,000 people. More than half of the basin is 24 • W A T E R E D U C A T I O N C O L O R A D O

public land, including the Rio Grande National Forest and the Great Sand Dunes National Park and Preserve. Those lands support a dynamic tourism industry that features activities like angling, boating, birdwatching and camping.

The northern third of the basin is considered a “closed basin” because it is separated, through a hydraulic divide, from the Rio Grande and therefore does not naturally contribute surface flows to the river. The Closed Basin Project delivers water from the closed basin to the Rio Grande for a few reasons: to help meet the state’s compact obligation to send water downstream to New Mexico and Texas, to maintain the Alamosa National Wildlife Refuge, and to deliver water to San Luis Lake.

Water use is limited by several interstate water sharing agreements. The 1938 Rio Grande Compact between Colorado, New Mexico and Texas requires that water be delivered to New Mexico at varying rates depending on the native flow of the Rio Grande each year. The 1944 Costilla Creek Compact, amended in 1963, divides the waters of a major tributary to the Rio Grande, giving roughly one-third of Costilla Creek’s water to Colorado and about two-thirds to New Mexico.

Dolores/San Juan/San Miguel River Basin The Southwest Basin encompasses nine distinct sub-basins, all of which flow out of state before they reach the San Juan River in New Mexico or the Colorado River in Utah.

Its major rivers are the San Juan, the Dolores and the San Miguel. The basin covers an area of about 10,170 square miles. Within it, the largest cities are Durango (population 18,500) and Cortez (population 9,000).

Most Southwest Basin headwaters originate on federal land owned by the U.S. Forest Service and the Bureau of Land Management. Federal agencies have worked with the Colorado Water Conservation Board’s Instream Flow Program to secure flow protection at high elevations throughout the basin. Many lower elevation lands are privately owned and used to raise cattle and grow crops like alfalfa, corn, wheat, hay and pinto beans.

Recreation is also a major economic driver in the basin, with tourists drawn from all over the country for rafting, skiing, fishing and mountain biking.

Waters from the southwestern part of the state are shared with neighboring states and tribes. The 1922 La Plata River Compact divides waters between Colorado and New Mexico, while the 1968 Animas-La Plata Project Compact recognizes that New Mexico has a right to divert and store water in Colorado for uses in New Mexico under the Animas-La Plata Federal Reclamation Project. Today, the Animas-La Plata Project primarily provides water to the Ute Mountain Ute and the Southern Ute tribes and to local and state agencies in Colorado, but it also provides water to the Navajo Nation and the La Plata Water Conservancy District in New Mexico. The San Juan-Chama Project, authorized in 1962, also moves water from the Southwest Basin’s Rio Blanco to the Rio Grande Basin in New Mexico.

The basin is home to the Southern Ute Indian Tribe and the Ute Mountain Ute Indian Tribe, the only two reservations in Colorado. The Colorado Ute Indian Water Rights settlement of 1988 allocated water for these tribes through the Dolores Project, where Dolores River water is stored in McPhee Reservoir, and the Animas-La Plata Project, where Animas River water is stored in Nighthorse Reservoir. The Animas-La Plata Project provided the tribes with a municipal and industrial water source to supply and augment future depletions of the San Juan River system that are constrained by the San Juan Basin Recovery Implementation Program for endangered native fish. It also provided the City of Durango and nearby areas with municipal and industrial water.

Some environmental challenges endure in the basin, such as coping with a legacy of abandoned hard rock mines that continue to impact water quality. This problem was brought into high relief in 2015, when U.S. Environmental Protection Agency workers mitigating pollution at the Gold King Mine near Silverton accidentally caused the release of 3 million gallons of water laced with metals into the Animas River. The spill affected municipal and agricultural water supplies as far away as Farmington, New Mexico, and Utah.

The San Miguel River, which runs through Telluride, serves as a water source for the small southwestern Colorado towns of Telluride, Norwood, Naturita and Uravan before it joins the Dolores River. The San Miguel through Telluride was heavily impacted by historical mining and channelized by an old railroad. Recently, the Town of Telluride has worked on restoring the river and creating public open space through its Valley Floor Project.

ADOBE STOCK

C I T I Z E N â&#x20AC;&#x2122; S G U I D E T O W H E R E Y O U R WAT E R C O M E S F R O M

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Colorado’s Groundwater Aquifers

G

roundwater plays a major role in Colorado’s water supply.

Nineteen of the state’s 64 counties—and about 20 percent of the state’s population—rely heavily on well water drawn from tributary and nontributary aquifers.

Tributary aquifers occur near rivers and streams and constantly interact with surface water flows. Because of this connection, tributary aquifers are regulated within the prior appropriation system alongside nearby streams.

Most of Colorado’s nontributary aquifers are in eastern Colorado, with some of them located in designated groundwater basins, which are regulated by the Colorado Ground Water Commission. These aquifers have little or no connection to surface water supplies and exist underground in deep geological formations, often in sandstone and limestone.

South Platte Alluvial Aquifer The South Platte Aquifer is a vast tributary aquifer that ranges from 20 feet deep under Denver to 200 feet deep 160 miles downstream in eastern Colorado. The aquifer contains about 8.3 million acre-feet of water, and it feeds—and is fed by—return flows from South Platte River diversions.

After Colorado’s 1969 Water Right Determination and Administration Act created augmentation plans, many South Platte well users obtained water-courtdecreed plans for augmentation, but others relied on annual State Engineer approvals to operate. Augmentation plans detail how groundwater users will mitigate impacts to the river caused by their well pumping.

This mitigation occurs through directly delivering water to the stream, releases of reservoir water, or accretions to the stream from delivery to recharge ponds. Those who failed to adopt augmentation plans could have their wells shut down by the State Engineer.

In 2002, the drought, combined with a change in the way water users called for their water, coincided with a court ruling to create a crisis. The Colorado Supreme Court determined that the State Engineer did not have the authority to approve temporary plans to augment well pumping depletions. With low river flows due to drought, diverters filling reservoirs placed an unprecedented call for water in the winter, requiring well users to replace stream depletions year-round. This doubled the amount of water required for 26 • W A T E R E D U C A T I O N C O L O R A D O

augmentation of well-pumping depletions at the stream. Well users scrambled to purchase additional water and complete water-court-approved augmentation plans, yet many could not find adequate augmentation water and the state ordered them to stop pumping. In the spring of 2006, more than 400 well owners in the South Platte Basin were ordered to stop pumping.

Even today, some of these wells remain shut down or curtailed due to a limited supply of affordable augmentation water in the central South Platte Basin. There are now more than 1,400 decreed augmentation plans in the basin.

San Luis Valley Aquifers The San Luis Valley is home to a shallow unconfined aquifer whose flows are connected to the Rio Grande and a deeper confined aquifer beneath it. Groundwater in the confined aquifer occurs under almost half of the valley and is tapped by deep wells with some from 1,000-2,000 feet deep, and others deeper. Water in the unconfined aquifer can be found at 12 feet or less below the surface of about half of the valley, though in places, wells reach more than 300 feet below the surface.

More than 3,000 wells operate in the San Luis Valley, irrigating one of the top three farming regions in Colorado—most wells tap the unconfined aquifer. However, years of drought and overuse have led to the decline of the unconfined aquifer. In the drought year of 2002 alone, the aquifer lost 439,000 acre-feet of water, and farmers

and water managers in the valley spent the next decade searching for a way to halt the aquifer’s decline.

By 2012, the Rio Grande Water Conservation District devised a system of regional groundwater subdistricts, defined by geography, that charge annual fees to farmers within their boundaries for each acre of land irrigated and each acre-foot of water used. Those funds are then used to buy water to offset groundwater depletions, either by injecting it back into the ground, sending it to users downstream, or paying cash to farmers injured by groundwater pumping. The subdistricts also pay farmers to fallow some of their land, lightening demand on the aquifer as a whole. The subdistricts continue to expand, with new sections of the valley adopting recharge programs through these subdistricts that are established with taxing authority.

Unfortunately, the dry growing season of 2018 reversed three straight years of gaining water levels. The collaborative project will continue to be adjusted until the aquifer’s long-term sustainability is ensured. If unsuccessful, the region could face a mandatory, state-ordered well curtailment in 2030.

Denver Basin Aquifers The Denver Basin Aquifer system consists of four aquifers underlying a 6,500 square-mile area from Greeley to Colorado Springs and from Limon to Jefferson County: the Dawson, Denver, Arapahoe and Laramie-Fox Hills aquifers. Water is found in sandstone beds, often as much as a half mile below the surface. Natural recharge is very slow, making them essentially nonrenewable. Water in each of the four Denver Basin bedrock aquifers is allocated to overlying landowners at a withdrawal rate of one percent per year for up to 100 years or until exhausted, whichever occurs first.

High-volume pumping has caused dramatic declines in groundwater levels, causing drops of as much as 40 feet per year in some areas. Between 1990 and 2002, water levels in some Arapahoe Aquifer wells declined by more than 240 feet, and some wells at the western edge of the basin began to dry up. To address

Colorado Groundwater and Surface Water Withdrawals, 2010

Groundwater Surface water

Percentage of groundwater to surface water withdrawals

Approximate total water withdrawal by county, in millions of gallons per day

100 1,000

500 SOURCE: U.S. Geological Survey

This map compares what percentage of total water supply comes from surface or groundwater in each county. Some counties rely almost exclusively on surface water, such as Larimer, Routt and Montezuma counties. By contrast, Baca, Kit Carson and Phillips counties get most of their water supply from groundwater.

this, counties such as El Paso, Elbert and Douglas have implemented more stringent pumping limits based on allocating water over 300 years.

As water levels decline, so does the rate and volume of water produced from each well, even as the cost of pumping goes up.

The point at which the cost for additional groundwater development exceeds the cost of acquiring renewable alternatives has been termed the “economic life” of the aquifer. Many communities are actively transitioning to renewable water sources.

Water sharing agreements like the Water Infrastructure and Supply Efficiency (WISE) Project between Denver Water, RALF TOPPER

Aurora Water and 10 water providers in the south metro area are intended to wean communities off of nonrenewable groundwater.

At the same time, many water providers are investigating using the Denver Basin Aquifer to store excess surface water in times of abundance, to withdraw it during dry times, a process called Aquifer Storage and Recovery (ASR). Compared to storing water in reservoirs, ASR would minimize water losses due to evaporation and require fewer permits because it is less disruptive than the construction of dams.

The Centennial Water and Sanitation District has been practicing ASR since

1994, and other providers now testing the practice include Denver Water, East Cherry Creek Valley Water and Sanitation District, and the City of Castle Rock.

High Plains Aquifer Often called the Ogallala Aquifer, the High Plains Aquifer underlies about 174,000 square miles of the central United States from South Dakota to Texas and New Mexico, including about 14 percent of Colorado. Its waters are critical to eastern Colorado’s agricultural economy, but the aquifer is being depleted at an unsustainable rate. The Colorado Division

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Principal Aquifers and Structural Basins of Colorado Colorado contains a variety of aquifer types. Alluvial aquifers (yellow)—also known as tributary aquifers, in which groundwater and surface water interact—consist of silt, sand and gravel. Sedimentary rock aquifers and valley fill aquifers (white) also hold vast amounts of groundwater. These include the Denver Basin, the High Plains Aquifer, and the San Luis Aquifer, among others.

Structural basin boundary Alluvial aquifers

Crystalline rock aquifers

Dakota-Cheyenne aquifer

Volcanic and igeous rock aquifers

Groundwater Wells by Use Domestic groundwater use occurs throughout the state but wells for irrigation, municipal and commercial use are most concentrated in the Denver Basin, High Plains Aquifer, San Luis Aquifer, and South Platte and Arkansas alluvial aquifers.

Domestic

Household use only

Irrigation

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Stock

Commercial

Municipal

of Water Resources estimates that farmers in eastern Colorado have drained an average of 850,000 acre-feet of water from the aquifer every year since large-scale pumping began in the mid-20th century.

The High Plains Water Level Monitoring Study, a congressionally-mandated effort that calculates changes in the aquifer’s water levels, estimates that the Ogallala has lost 273.2 million acre-feet of water since 1950.

In some of the heavily used parts of the aquifer, water levels have dropped 50 to 100 feet since 1950; lighter-use areas have dropped between 5 and 50 feet. Many shallow eastern Colorado wells have gone completely dry.

To combat this decline, voluntary or mandatory conservation programs have been organized. Some programs are sponsored by the U.S. Department of Agriculture, like the Conservation Reserve Enhancement Program through the Farm Services Agency or the Ogallala Aquifer Initiative from the Natural Resources Conservation Service. These programs offer financial incentives to convert irrigated cropland to dryland farming or to permanently retire irrigation wells and fields. Other initiatives, like the Master Irrigator Program, come from local groundwater management districts and help increase farmers’ irrigation efficiency. They have proven effective at cutting groundwater use without dramatically impacting farmers’ livelihoods. Groundwater levels are still declining in most areas, but the rates of decline are decreasing.

In 2004, the Colorado State Legislature created the Republican River Water Conservation District in northeastern Colorado to help the region comply with the Republican River Compact. The district promotes conservation by offering financial incentives to producers who voluntarily retire water rights to reduce consumptive use primarily of groundwater.

The district is buying and retiring irrigated land and the associated water rights, or paying farmers to fallow it in order to comply with the compact. However, fewer conservation efforts are underway in southeastern Colorado, and some engineers say that wells there could dry up within 15 or 20 years.

TOP: COLORADO GEOLOGICAL SURVEY; BOTTOM: COLORADO DIVISION OF WATER RESOURCES

Fields in the arid San Luis Valley show the region's reliance on groundwater through center pivot irrigation.

SanLUIS LuisVALLEY ValleyAQUIFER AquiferDYNAMICS Dynamics SAN Two stacked aquifers lie beneath the floor of the San Luis Valley. The unconfined aquifer is much shallower, while the confined aquifer is trapped between clay layers deep underground. Water recharge and discharge occurs to different degrees in both aquifers, with some interaction between the two.

The dynamics are still not fully quantified.

UNCONFINED AQUIFER Shallow alluvium

CONFINED AQUIFER Clay-rich confining layers, Alamosa and Santa Fe Formations

Precipitation

Evapotranspiration of surface and groundwater

Streamflow recharge Mountain front recharge

Withdrawal from wells and drains Discharge to streamflow V LU AL AY CL CL AL

DEEPER ROCK LAYERS Non-productive

Groundwater outflow

SA

IUM

AY

AM NT

OS

A

A

FE

FA

TS UL

NOT TO SCALE

TOP: CHRISTI BODE; BOTTOM: WATER EDUCATION COLORADO

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As Colorado’s population continues to grow, new development and water to meet the needs of the population is needed. The population is projected to grow from more than 5.6 million today to between 7.7 million and 9.3 million by 2050.

Looking Forward

W

here your water comes from depends on where you live.

Although many Colorado water providers, water users, ditch companies, and communities have worked to build resilient systems, the future is not without its challenges when it comes to accessing or providing clean and ample water. Climate change and its impacts, including an increased incidence of flooding, drought, wildfire and other extreme events threaten both water quality and quantity and can even create the need for new infrastructure.

Climatic and other water supply challenges are exacerbated by rapid population growth. The state has grown from 1 million people in 1930 to more than 5.6 million today, according to the Colorado State Demography Office. The population is projected to increase to between 7.7 million and 9.3 million by 2050, according to the 2019 Analysis and Technical Update to the Colorado Water Plan. Although per capita water usage is expected to decrease in the future, more Coloradans will likely mean an increased demand for water.

According to the technical update, even with aggressive conservation efforts, municipal 30 • W A T E R E D U C A T I O N C O L O R A D O

and industrial water demand is projected to increase by 35 to 77 percent by 2050, creating a gap between future water supply and demand for municipal and industrial uses of between 250,000 acre-feet to 750,000 acre-feet by 2050. At the same time, agricultural water demand may increase as the climate warms. The technical update projects gaps in agricultural water availability increasing by 440,000 acre-feet per year to 1,053,000 acre-feet per year.

In the face of scarcity, the water that pours from taps, irrigates fields, and flows in rivers is more valuable than ever, but that does not mean that the future is limited. The

Colorado Water Plan lays out a roadmap for Coloradans to cooperate with each other in the use and management of the public’s water resources. The plan, published in 2015 says: “We are galvanized by our challenges: drought, wildfire, flooding, climate change, and unprecedented growth. And we are energized by our capability … If we are wise stewards of our water resources, Colorado has enough water to meet our state’s future needs.”

The water plan looks to meet not just the needs of cities, towns, and agriculture, but also the water needed to support the environment and recreation.

As water challenges intensify, Coloradans can begin to engage by knowing their river basin and local watershed, understanding the sources of their water supply, and getting to know the other people and uses that depend on the same water. With this information, stakeholders can identify challenges, have discussions and build relationships to understand different perspectives. From this place of understanding, Coloradans can develop solutions to live within the means of available water. It’s the responsibility of all Coloradans to engage, share their voices, and help plan for a sustainable water future that meets many values.

ADOBE STOCK

Resources ONLINE Colorado Climate Center climate.colostate.edu Colorado Department of Public Health and Environment’s Water Quality Control Division colorado.gov/pacific/cdphe/wqcd Colorado Division of Water Resources water.state.co.us Colorado Geological Survey’s Groundwater Atlas of Colorado coloradogeologicalsurvey.org/water/groundwater-atlas Colorado Water Conservation Board cwcb.state.co.us Colorado Water Plan and the Basin Roundtables colorado.gov/cowaterplan National Integrated Drought Information System (NIDIS) drought.gov/drought Natural Resources Conservation Service Snow Telemetry (SNOTEL) and Snow Course Data wcc.nrcs.usda.gov/snow U.S. Geological Survey Current Water Data for Colorado waterdata.usgs.gov/co/nwis/rt Water Education Colorado watereducationcolorado.org WateReuse Colorado watereuse.org/sections/watereuse-colorado

REPORTS AND ARTICLES Brad Udall and Jonathan Overpeck, The 21st Century Colorado River Hot Drought and Implications for the Future, Water Resources Research (2017).

Colorado State Forest Service, 2018 Report on the Health of Colorado’s Forests (2018).

Colorado State Forest Service, Colorado Statewide Forest Resource Assessment (2009).

Jeff Lukas, Joseph Barsugli, Nolan Doesken, Imtiaz Rangwala, Klaus Wolter, Climate Change in Colorado (2014).

NOAA National Centers for Environmental Information, State Climate Summaries Colorado (2019).

Nolan Doesken, Roger Pielke, Sr., Odilia Bliss, Climatography of the United States No. 60 (2003).

Philip Mote, Sihan Li, Dennis Lettenmaier, Mu Xiao, Ruth Engel, “Dramatic Declines in Snowpack in the Western US.” npj Climate and Atmospheric Science, 1 (2018).

Reagan Waskom, “An Alternative Perspective on Water Use in Colorado.” Colorado Water, (2003).

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Publication of Water Education Colorado's Citizen's Guide to Where Your Water Comes From is made possible by the generous support of sponsors.

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