Leadership Development Module: Flooding

Module 1: flooding

Houston floods. The city has experienced three 500-year flood events in the last three years: the Memorial Day Floods of 2015, the Tax Day Floods of 2016, and Hurricane Harvey in 2017. Understanding future flooding risk, strategies to manage water, who is responsible for our drainage infrastructure, and the related policy will allow residents and neighborhood leaders to better advocate for appropriate solutions in their neighborhoods.

This module will explore the causes of flooding, how rain water is managed at different scales, and what residents of Houston and Harris County should be aware of in regards to flooding post-Harvey.

Why do places flood?

Flooding happens when an area gets more rain than its soil and infrastructure can absorb or move. Rainwater, also called stormwater, is ideally absorbed into the soil, and the rain that isn’t absorbed “runs off” over rooftops, streets and parking lots into bayous, rivers, or the Gulf. When it rains so much that the water can not be absorbed, the bayous fill up, and the infrastructure can’t move or hold the water, the result is flooding.

Adding roads, driveways, parking lots, rooftops, and other surfaces increases the amount of stormwater runoff, and makes it harder for water to soak into the ground.

Pavement and rooftops shed water.

Storm drains deliver water directly to waterways.

Trees and other vegetation break the momentum of the rain, help reduce surface erosion, and help give the soil time to absorb.

Wetlands are areas where water accumulates sometimes or all the time. Wetlands are a critical part of watersheds and flood control. They help detain stormwater, control erosion, store and clean water, and provide places for recreation if planned thoughtfully.

When wetlands are destroyed by new developments, these benefits are also lost.

Water pools in low lying areas and filters into the soil.

Streets act as streams, collecting stormwater and channeling it into waterways.

Roots anchor soil minimizing erosion.

Urban waterways, such as the bayous, are a key part of managing water in the city.

Pollutants collected on impervious surfaces are washed into streams, rivers and lakes.

The top causes of flooding in Houston are:

LOW LYING CITY:

HOUSTON’S GROWTH:

AGING INFRASTRUCTURE:

TRANSPORTATION:

Houston is relatively flat, only 50 ft above sea level. We have a high clay content in the soil, making it harder for water to absorb. Additionally, the underground water table is very high, which means the ground is already saturated and can’t absorb more water.

The increase in impervious surfaces and the loss of natural ways to collect and filter water both increase flooding and impact the quality of water. Recent research shows that almost 30 percent of freshwater wetlands in Harris County were lost from 1992 to 2010.

Experts agree that Houston flood control system is outdated. The current flood management infrastructure is nearly a century old and was designed for small scale flood prevention, making it insufficient to handle increasingly intense rain events.

Roads, freeways, railroads, and other infrastructure can change the way water moves and how fast it moves. Freeways can create areas where water accumulates, leading to localized flooding when the quantity of water is too great and backs up the flow.

How do we manage water?

There is not a single solution to eliminate flooding in Houston, but there are a number of ways to minimize its impact.

Some key strategies to manage stormwater include: planting trees and plants, building and maintaining drainage infrastructure to collect and move water away, and reducing the amount of surfaces that don’t absorb water. Managing stormwater and its runoff is called stormwater management. In understanding drainage infrastructure, we hope to better understand how new projects meet the goals of moving water and protecting our water quality.

Two key elements in stormwater management are: conveyance systems (moving water) and retention or detention systems (holding water). The majority of stormwater infrastructure achieves one or both of these purposes. When determining how to manage water, and the types of infrastructure needed to achieve water management goals, there are two primary systems: Conventional and Low Impact Development (LID).

n Evapotranspiration

By Plants

Runoff can carry polluted material over impervious surfaces.

CONVENTIONAL STORMWATER MANAGEMENT SYSTEMS Conventional drainage management systems focus primarily on storing water or moving it as fast as possible through underground or aboveground drainage systems that include pipes, curbs, and gutters, or in collecting and storing water in large basins like detention ponds. Conventional infrastructure is typically concrete, plastic, metal or other impervious materials.

On a large regional scale, conventional conveyance and retention systems are necessary, particularly during a large rain event, tropical storm, or hurricane. However, conventional systems have limited water quality treatment and infiltration.

Which one is better?

The answer is that we need both, but in the future the question should be which system—or combination of the systems—is the most appropriate for our communities. Implementing stormwater management at different scales will build our capacity to protect lives and property from intense flood events.

Filtered Runofff

Absorption by Soil And Plants

LOW IMPACT DEVELOPMENT AND GREEN INFRASTRUCTURE SYSTEMS Low impact development (LID) manages stormwater by reducing the impact of development and promoting the natural movement of water. These practices include controlling water movement (flow), retaining or holding rainwater, infiltration, and treating contaminants in the water.

At the lot, neighborhood, and municipal scale, LID strategies are highly effective at reducing runoff and managing the conveyance and retention of water—in some cases at a lower cost. LID has been shown to improve the quality of water and provide more visually attractive solutions than conventional drainage systems. The Bayous are a local example of LID.

Why is understanding drainage infrastructure important to me?

Drainage infrastructure varies in size, scale, and purpose, yet it is meant to work together to keep our homes, businesses, and communities safe. Understanding how it works and where it might not be working is important to mitigating any potential hazards and improving our neighborhoods.

Knowing who plans, builds, and maintains infrastructure will help your community advocate for your drainage needs.

Your home and property are a part of the regional drainage system, and there are things you can do to lessen the effects of regular flooding.

As new drainage projects and funding come up in your community, it is important for your input to be heard. Understanding the types of infrastructure, their purpose, and who controls them will help you feel more prepared.

The city and county are changing flood protection regulations, and it is important for you to understand what these regulations mean.

How does our drainage infrastructure works?

Water can be drained through natural and artificial means. This means that when it rains, some water naturally seeps into the ground, and the rest is either collected or carried away through a network of drainage infrastructure moving the water through neighborhoods into water bodies, bayous and man-made floodways. Drainage infrastructure is a key part of stormwater management. Current drainage infrastructure ranges from small-scale neighborhood drainage ditches­and underground pipes to large-scale ­dams, floodways, and levees. This system is meant to work together to support water management across the region.

MUNICIPAL SYSTEMS:

NEIGHBORHOOD SYSTEMS:

PRIVATE LOT:

The size and complexity of municipal systems depend greatly on the size and wealth of the municipality. Common types of municipal drainage infrastructure include storm drains, piped drainage infrastructure, floodways, bayous, and water reservoirs.

Expanding the capacity of bayous is an example of an improvement to the municipal system.

Neighborhood drainage systems are a key element of the larger municipal drainage system. The most common form of drainage infrastructure are drainage ditches.

These ditches, often collect the runoff from the streets and move the neighborhoods water to a larger drainage system. Other examples are street curbs that lead to storm and sewer drains.

Private lot drainage infrastructure is the smallest scale but can have a significant impact—particularly when a majority of lot owners have properly-maintained infrastructure that effectively collects, holds, and conveys water. Private lot infrastructure strategies include: rain gardens, vegetated swales, and rain barrels.

Small-scale strategies, such as regrading lots or widening ditches to detain small volumes of water, can reduce the impacts of flooding in neighborhoods. Keeping the ditches clear of debris, not filling them in with dirt, and retrenching from time to time can mitigate flood risk. Residents can call 311 to report issues with ditches and storm drains. The Storm Water Maintenance Branch provides regrading of ditches and debris removal.

Who is in charge of our drainage infrastructure?

Neighborhood Groups: Neighborhood groups like TOP Chapters and Super Neighborhood Councils serve as a forum where residents and stakeholders can discuss issues affecting their neighborhood, reach a consensus on projects, and develop a neighborhood action plan for community improvements.

Neighborhood

Civic structures or organizing groups in neighborhoods are one way that City Departments and City Council can work more effectively with residents, be responsive to communities, and deliver city services and needed improvements promptly and efficiently. This is one way to advocate for drainage improvements in your community.

Houston Planning and Development: As the 4th largest city in the United States, Houston’s Planning and Development Department has a broad range of responsibilities. Their primary responsibility is to review and approve new construction and development plans, thoroughfare plans, complete streets, bike lanes plans and annexation—all of which impact the city’s stormwater demand and capacity.

City

Houston Public Works: Houston Public Works’ responsibilities include operation and maintenance of the City’s streets and drainage, production and distribution of water, collection and treatment of wastewater, and permitting and regulation of public and private construction.

Harris County Engineer Department: The Harris County Engineer department play a role in ensuring new developments in unincorporated areas will not pose a threat to the safety and welfare of the public as prescribed by Commissioners Court. This department enforces all Harris County regulations and reviews and approves new developments.

County

Statee

Harris County Flood Control District: The Harris County Flood Control District, which is run by the County Commissioners, provides flood damage reduction projects that work, with appropriate regard for community and natural values.

Flood damage reduction is accomplished by: 1) Devising flood damage reduction plans; 2) Implementing plans; and 3) Maintaining infrastructure.

Texas Water Development Board: The Texas Water Development Board is a state agency that provides information, education, and support to local agencies. They support planning, financial assistance, and outreach for the conservation and responsible development of water for Texas. TWDB is not a regulatory agency, which means it doesn’t make or enforce any regulations, statutes, or laws. Instead they use their resources for water planning, data collection and release, financial assistance, and technical assistance services to local jurisdictions and communities.

What should I know right now?

CHAPTER 19 FLOODPLAIN ORDINANCE: The City of Houston approved revisions to Chapter 19 Flooding Ordinance.

The revisions seek to ensure new dwellings are built high enough to save lives and property in the event of flooding.

The revised ordinance would affect 85,000 more families than the current regulations. Houston’s current code only applies to properties in the 100-year floodplain and requires building 1 foot above 100-year flood elevation. The proposed revisions would include properties in the 500-year floodplain and require building 2 feet above the 500year flood elevation for both areas. It would also include a no net fill regulation in the 500-year floodplain.

1% flood chance (100 YR)

BEFORE 1981 Before floodplain regulation

0.2% flood chance (500 YR)

Current Regulations Built 1 ft above 100-Year flood elevation

Proposed Regulations Built 2 ft above 500-Year flood elevation

BUYOUTS: Home buyouts are a process by which governmental entities purchase homes in flood-prone areas.

The goal is to enable vulnerable families to find housing that is safe from flooding, while freeing up land for flood mitigation investments like bayous expansion. Home buyouts are used by the Flood Control District to reduce flood damages in areas hopelessly deep in the floodplain where structural projects (i.e. channel modifications or detention basins) to reduce flooding are not cost effective and/or beneficial. During the buyout process the Flood Control District will offer the family the pre-flood appraisal value and relocation assistance.

BEFORE BUYOUT PROCESS:

BUYOUT CANDIDATE Deep in the 100-year floodplain, structural modifications are not cost effective or feasible to reduce or avoid flood damage.

NOT IDEAL CANDIDATE

NOT IDEAL CANDIDATE

Partially in the 100-year floodplain.

Structural modifications would address flooding in this area.

Outside of the floodplain, rarely floods from out-of-banks bayou flooding.

AFTER BUYOUT PROCESS: CHANNEL MODIFICATIONS

NEW DETENTION BASIN (potential park space)

Pros: Family is relocated to higher ground, out of harm’s way, eliminating future flooding risk and need for future flood insurance or federal assistance. The floodplain is restored to its natural and beneficial function for stormwater storage. The land made available through buyouts allows for further structural improvements.

Cons: The Flood Control District does not usually move quickly to buy people out. The community will have to come together to make sure people are compensated fairly to acquire a decent house in a neighborhood of their choosing.

Important concepts 500 YEAR FLOODPLAIN: The area of land that has a 0.2% chance of being flooded from a bayou, stream or creek in a

given year. Statistically, the 0.2% (500-year rain) flood has a 6% chance of occurring during a 30-year period of time.

However we have had three 500 year floods in the last three years. The 0.2% (500-year) floodplain is referred to as Zone X for insurance purposes on Flood Insurance Rate Maps (FIRMs).

100 YEAR FLOODPLAIN: The area of land that has a 1% chance of being flooded from a bayou, stream or creek in a given

year. Statistically, the 1% (100-year rain) flood has a 26% chance of occurring during a 30-year period of time. The 1% (100-year) floodplain is the Base Flood or Special Flood Hazard Area. It is referred to as Zones AE, AO, A, or VE for insurance purposes on Flood Insurance Rate Maps (FIRMs). Properties located in these mapped zones are required to have flood insurance if the owner has a federally backed mortgage on the property.

BASE FLOOD ELEVATION: The elevation above the average sea level that waters from a 1% (100-year) flood chance will

reach at a given point along a creek or bayou. These elevations are determined using hydrology and hydraulic computer models. The elevations are then mapped on the topographic data for the county to define the 100-year floodplain.

CONVEYANCE: The ability of a channel or other drainage element to move stormwater. The Conveyance Zone is the

portion of the Special Flood Hazard Area that is utilized to move water during the occurrence of the base flood.

FLOODPLAIN: The area of land that gets inundated when bayous and creeks come out of their banks due to heavy

rainfall. Residences and businesses within the floodplain are considered to be at risk of being damaged by flooding.

FLOODWAY: The area of the floodplain that should be reserved (kept free of obstructions) to allow floodwaters to move

downstream. The floodway is where the water is likely to be deepest and where it will be moving the fastest.

HYDROLOGIC: The water cycle, also known as the hydrologic cycle or the H2O cycle, describes the continuous

movement of water on, above, and below the surface of the earth. The amount of water on Earth remains fairly constant.Water moves from one place to another, such as from river to ocean, or from the ocean to the atmosphere, through the processes of evaporation, condensation, precipitation, infiltration, runoff, and subsurface flow. In so doing, the water goes through different phases: liquid, solid (ice), and gas (vapor).

NET FILL: The placement of any fill material that results in any increase in the surface elevation of a property from its

natural or pre-development state.

PERVIOUS: A material that allows water to pass through. “Permeable� is also used to describe the degree to which a

material allows liquid to pass through.

WATER TABLE: Is the top level of an underground surface in which the soil or rocks are permanently saturated with

water. The water table fluctuates both with the seasons and from year to year because it is affected by climatic variations and by the amount of precipitation used by vegetation; it can also be affected by withdrawing excessive amounts of water from wells or by recharging them artificially.

STORMWATER: Stormwater is rainwater or melted snow that runs off streets, lawns, and other sites. When stormwater

is absorbed into soil, it is filtered and ultimately replenishes aquifers or flows into streams and rivers.

TOP’s principles for flood control It is the responsibility of the government to protect communities from flooding as much as is possible. Flood management for an area should be determined through a transparent, participatory neighborhood by neighborhood assessment to inform flood mitigation recommendations. If no safe alternatives exist, these recommendations could potentially include moving residents out of harm’s way and with the full input and discussion from the community. In addition, any buyouts should ensure that residents are given adequate funds to move to a decent neighborhood with the same indebtedness as they currently have.

Public participation and transparency is vital to ensure an equitable and sustainable recovery process. Houston communities should be engaged in all phases of the decision-making process regarding recovery, reconstruction, flood mitigation and future infrastructure investments to protect communities from flooding.

The city of Houston should share clear information to all Houstonians about: (1) where are the low lying areas that likely cannot be protected by improving the drainage system, even after the bayous are improved, (2) which bayous or waterways have plans for improvement, (3) how low- and moderate-income families, particularly African-American and Latino families, who already live in a flood prone areas, will be assisted in keeping their homes safe from flooding and raising their houses to the proposed needed level.

Any flood control efforts should count equally each household effected. Flood mitigation priorities should not be based on a cost-benefit analysis based on the sales value of the homes because this has a discriminatory effect, partly due to the underinvestment in some neighborhoods.

The city must ensure that families in traditional African-American and Latino neighborhoods are not forced to sell to high priced developers because they are unable to raise their houses. This would be the government not doing its duty with the benefit accruing to developers. People who live in neighborhoods now must be able to stay if they choose – the Right to Stay and the Right to Equal Treatment are key pieces of TOP’s hurricane recovery platform.

IMAGE REFERENCES:

1. Cover Photo: Elaine Morales-Diaz/buildingcommunityWORKSHOP. 2. Low Lying City Photo: Houston Skyscrapers, goodfreephotos.com 3. Houston’s Growth Aerial Image: Houston 1984 and Houston 2018, Google Earth 4. Aging Infrastructure Photo: Bill Jacobus/flickr.com 5. Transportation Photo: Aerial View Houston Highways, pixabay.com 6. Which One is Better Photo: D. A. Horchner/Design Workshop, Inc. 7. Municipal Systems Photo: Harris County Flood Control District.

The purpose of this series is to build an informed and engaged resident base, support organizing efforts and build the capacity of neighborhood leaders to impact disaster recovery planning and prioritize future development in 7 neighborhoods of Houston.

Texas Organizing Project T TX 77004 24044 Caroline St, Houston, 832.582.0061

buildingcommunityWORKSHOP 708 S Main St, Houston, TX 77002 712.304.6277