5 1 small little topashaw creek case study

Short course for UNIVERSIDAD NACIONAL DE INGENIERIA January 26-29, 2016

PLANNING AND DESIGN FOR REHABILITATION OF RIVERS USING LARGE WOOD METODOLOGÍA PARA REFORESTAR RÍOS DEGRADADOS POR ACTIVIDADES HUMANAS USANDO TÉCNICAS DE BIOINGENIERÍA

5.0 Little Topashaw Creek Case Study

Shields et al. 2008. Ecology and Society. 13 (2): 54

Shields Engineering LLC

Course overview Day I (Jan 26)--Foundational topics

•

Constructability assessment

•

Introductions

•

Case study II—Trinity River, California

•

Review of information resources (design handbooks and spreadsheets) for large wood

•

Monitoring

•

Is wood appropriate for your site?—criteria for screening (Planning)

•

Three design approaches

•

Key issues for large wood design

Day 2 (Jan 27)—Designing large wood structures •

Case study I—Little Topashaw Creek, Mississippi

•

Design life for wood structures/selection of design event or condition

•

Types of wood structures

•

Findings of recent research on drag and lift coefficients

•

“Road testing” selected design spreadsheets

Day 3 (Jan 28)—Risk, uncertainty and construction •

Sensitivity and Monte Carlo analyses

Day 4 (Jan 29)--Field trip

2

PRE PROJECT CONDITIONS An incising, sand bed stream

Little Topashaw Creek Watershed Modified reach •4th-order stream •Watershed area = 37 km2 •Maximum relief ~ 65 m •Mixed cover land use •Warmwater stream •Incising channel network •Agricultural and forestry land uses

Channel constructed in 1913

1941

1996

Little Topashaw Creek •Bed slope = 0.0025 •Sinuosity = 2.1 •W~33m, D~3.6m •Mean width has increased 45x since ~1955 •Simon stage IV/V.

Incised channel CEM

% finer than

100 75 50 25 0 0.01

0.1

1

10

Grain size, mm

Bed material is sand 0.2-0.3 mm

Outcrops of cohesive material are common

Let’s take a look around…before adding wood

CH/MH SM SP-SM SC-SM CL-CH CL

62 m

Changes since 1999

2001

2002

Mean wavelength

2%

3%

Mean meander length

-7%

-5%

Mean amplitude Mean radius of curvature

-14% -13% 26%

23%

n = 23

1999

1999

Ecological status before rehabilitation • Vegetation dominated by opportunistic and invasive exotic

species with remnants of old floodplain forest. Succession within enlarged channel hindered by rapid sedimentation.

• Flashy hydrology—almost no overbank flow • Water quality issues (sediments, pesticides, nutrients)

• Depressed levels of POM in bed sediments • Higher levels of LWD, but unstable • Shallow depths (5 cm), unstable substrate

• Fish and invertebrate collections typical of streams impacted

by erosion and sedimentation

Aquatic Habitat Water Depth, cm 30 25 20 15 10 5 0 Before

After

Reach modified by LW

Before

After

Downstream Reach

Large wood Density , m2/100 m 2 50 45 40 35 30 25 20 15 10 5 0

Water Width, m 10 8 6

4 2 0 Before

After

Reach modified by LW

Before

After

Downstream Reach

Before

After

Reach modified by LW

Before

After

Downstream Reach

Invertebrates before/without wood addition % of captures by substrate type 16

% composition by functional feeding group 3.2 2.8 1.9

6

10.7 Filtering collectors

78

Leaf Packs

Gathering Collectors

Sediment

Shredding herbivores

Wood

80.9

Scrapers Predators

Fish family composition Percent of biomass as centrarchids

Percent of biomass as cyprinids 60 50 40 30 20 10 0

100 80 60 40 20 0 Before

After

Reach modified by LW

Before

After

Downstream Reach

Before

After

Reach modified by LW

Before

After

Downstream Reach

REHABILITATION PROJECT This is where we added wood

Purpose of project “The purpose of large wood structures placed in an incised, sand-bed stream is to accelerate evolution toward a sinuous, two-stage channel with wooded berms….”

Rehabilitation • 2 km reach treated, but 4 km were

studied (1999-2004) • Large woody debris structures • Willow planting • Vegetated inlets—gully

stabilization by planting switchgrass sod

LW structure design

Steps in constructing LW structure

Anchor Installation 58 of the 72 LWS were anchored using four Duckbill Earth Anchors (138-DB1) each.

Each anchor was driven into the ground by pressing with a metal rod and a track hoe bucket and then load tested to 1000 lb (4.5 kN).

Top View of a Completed LWS (note the crossing cables)

Completed LWS and willow planting

Construction costs in 2000 (USD)

• Debris structures

$80 m-1

=(19% to 49% of recent costs for stone treatments)

• Willow planting

$7.42/cutting

Large wood structure dimensions • N = 72 • Crest elevation = 2.1 + 0.5 m • Dimensions: 14 m long by 5.3 m wide • 4.4 key members and 14.7 racked

members per structure • Diameter of key members = 45 cm • Spacing = 13.8 + 10.8 m • Cost = $80 m-1 treated bankline (~1/3 the

cost of stone toe)

Were promising!

INITIAL RESULTS

Little Topashaw Creek Discharge, m3/s

WY 2000 60 Construction of 72 LWS

0

WY 2001

60 68 LWS remaining

0 1-Oct

29-Jan

29-May

26-Sep