stream restoration in the urban environment

Stream Restoration in the Urban Environment Concepts and Considerations

The Restoration of Our Rivers; October 5, 2012

Matthew A. Van Eps, PE & Sandi J. Formica: Watershed Conservation Resource Center

What is Stream Stability?

Ability of a stream, over time, in the present climate to

transport sediment and streamflow produced by its

watershed in a manner such that the stream maintains

its dimensions, pattern, and profile without either

aggrading or degrading (Rosgen, 1996)

2004 (Post Flood)

2002 (Pre-Flood)

Streambank Erosion

Is this river stable?

April 2010 March 2011

Erosion in the Urban Environment

11 ft

Why Does it Matter?

Impacts to Infrastructure

Creates Safety Concerns

Decreased Aesthetics

Water quality impacts

Property Loss

Lowering of Water Table

Effects on Aquatic Habitat

Etc.

What Causes Stream Instability?

Sediment Supply

Streamflow

Dimension (Cross-Section)

Pattern

Profile

Change to any one variable in the definition of stability can cause an imbalance

Ability of a stream, over time, in the present

climate to transport sediment and streamflow

produced by its watershed in a manner such

that the stream maintains its dimensions,

pattern, and profile without either aggrading

or degrading

Examples of Cross-Section Change

Channel excavation and cross-channel obstructions result in deposition, over-widening, and lateral erosion of streambanks.

Low water crossings

Channel enlargement projects

Water lines

Check dams

Etc.

Examples of Pattern Change

Straightening of urban channels increases stream slopes and raises the erosion potential

Development

Flood Control

Transportation projects

Etc.

Examples of Profile Change

Changes in slope can result in greater potential for localized scour and downstream instability

Utility crossings

Flood control

Linear road projects

Etc.

Changes in Stream Discharge caused by changes in land use

Forest to Pasture

(Qforest to Qpasture)

Pasture to Impervious

(Qpasture to Qimpervious)

Forest to Impervious

(Qforest to Qimpervious)

Reservoirs

1980 (forested)

2004 (cleared)

Change in Sediment Supply

Reduction or Increase in Sediment Supply Can Cause Instability

Decrease Supply

Armoring Channels

Reservoirs

Land-use Changes

Increase Supply

Streambank Erosion

Mass Wasting

Construction Sites

Common Approaches to Improving/Maintaining Channel Stability

Armoring Banks

Bank Stabilization

Straightening

Do Nothing

Channel Clearing

Bioengineering

Natural Channel Design

Natural Channel Design

Seek to Restore: Dimension, Pattern, and Profile using data from a stable stream reach.

Same stream type in the same valley type

Consider the Natural Tendencies of the Stream!

Urban Stream Restoration Considerations

Niokaska Creek – Gulley Park

Project Goals Demonstrate an urban stream restoration using a natural channel design approach

Niokaska Creek – Sweetbriar Park Mullins Branch

Project Partners & Funding

Urban Stream Restoration Typical Objectives

Reduce streambank erosion

Improve water quality

Protect infrastructure

Reduce safety concerns

Provide amenity to public

Enhance aquatic habitat

Re-establish riparian areas

Improve aesthetics

Public outreach

Site Selection

Sites Identified by partners

Selection criteria

Internal or public priority

Risks to infrastructure

Safety concerns

Water quality concerns

Probability of success

Visibility of project

Site Characteristics

Drainage Area Niokasaka – Gulley: 1.25 mi2

Niokasaka – Sweetbriar: 4.8 mi2

Mullins Branch: 0.75 mi2

Impervious Surfaces

USGS gage station at two sites

1,000 to 1,600 feet

Incised channels (common) Decreased sediment supply

Increased streamflow

4 to 8 ft. high eroding streambanks

Rosgen Stream Classification: B4c

Site Characteristics

Drainage Area Niokasaka – Gulley: 1.25 mi2

Niokasaka – Sweetbriar: 4.8 mi2

Mullins Branch: 0.75 mi2

Impervious Surfaces

USGS gage station at two sites

1,000 to 1,600 feet

Incised channels (common) Decreased sediment supply

Increased streamflow

4 to 8 ft. high eroding streambanks

Rosgen Stream Classification: B4c

Pre-Restoration Site Monitoring Streambank Erosion Analysis

Establish Site Monitoring

Quantify water quality benefits

Sample bank materials

Estimate annual loads:

Niokaska - Sweetbriar

Sediment – 2,000 ton/yr

Total Phosphorus – 600 lb/yr

Total Nitrogen – 1,600 lb/yr

Stream Restoration Design Development Typical Site Constraints

No change to 100 year flood elevation or revised flood map($$)

Infrastructure Trails/Sidewalks

Bridges

Sewer Lines

Water Lines

Stormwater outfalls

Fixed flood prone width

Adjacent buildings

Vegetation preservation

Presence of public Controlling access

Communicating intent

Stream Restoration Design Detailed Data Evaluation

Topographic Survey

Geomorphologic Analysis

Hydrology Analysis

Step-wise Engineering Process Reference reach data

Dimension, Pattern, Profile

Flow Capacity

Sediment Transport

Bankfull Discharge: 130 cfs

Design Cross Section: 30 ft2

Bankfull Slope: 0.01180 ft/ft

Bankfull Shear: 1.04 lb/ft2

Stream Restoration Design

Reference Reach – Provides a blueprint from which design variables can be developed

Control near-bank shear forces

Maintain desired pool depth

Provide grade control

J-Hook vanes

Cross vanes

Rock Sizing Based on shear force

Flat edges

Bigger is usually better

Structure design Length ≈ Wbkf

Angle ≈ 20°

Slope = 5%

Stream Restoration Design In-stream Structures

Cross Vane

J-Hook Vane w/step

Stream Restoration Design Re-vegetation Plans

Critical Element of the Restoration Design Provides stability

Habitat

Forage

Aesthetics

Consult with local specialists

Locate plants based on sun & water needs Inland Sea Oats, Prairie Drop Seed

Button Bush, Spice Bush

Green Ash, Plum, Wafer Ash, Sycamore

Irrigate through 1st summer (at least)

Additional planting in late fall

Implementation Schedule

Construction Site Preparation – 1 to 6 months Apply and obtain applicable permits

Apply and obtain no-rise certification

Select, order, and move rocks to site

Utility line and other infrastructure location

Order and obtain other materials, such as, erosion control, plants, compost, etc.

Construction (heavy) (Depends on Scale, Complexity)

Earth work and constructing new channel and floodplain/bankfull benches

Constructing rock structures

Construction (finishing) – two to three months Touch-up work on structures

Building soil mattresses

Planting

Expect Post Construction Rain If you build it, IT WILL RAIN

T-storms, Tropical Storms, Tropical Depressions

(you name it!)

Niokaska Creek at Gulley Park Upstream - Before Restoration

Infrastructure Constraints

Elevated Sewer Line

Fiber Optic Line

Niokaska Creek at Gulley Park Upstream - After Restoration

After two years Cross-Vane to direct flow

and create backwater

Force water over SSL to

improve aesthetics

Niokaska Creek at Gulley Park Upstream - After Restoration

After four years

Improved access point

Niokaska Creek at Gulley Park Mid Section – Before Restoration

Incised Channel

Niokaska Creek at Gulley Park Mid Section – One Week After

Incised Channel

Terrace Elevation

Bankfull Elevation

Use of rock along toe

Niokaska Creek at Gulley Park Mid Section – One Year After Restoration

Niokaska Creek at Gulley Park Mid Section – Two Years After Restoration

Niokaska Creek at Gulley Park Mid Section – Four Years After Restoration

Niokaska Creek at Gulley Park Lower Mid Section – Before Restoration

Trail Encroachment

Niokaska Creek at Gulley Park Lower Mid Section – Before Restoration

Trail Encroachment

Niokaska Creek at Gulley Park Lower Mid Section – After Restoration

Niokaska Creek at Gulley Park Lower Mid Section – One Year After Restoration

Niokaska Creek at Gulley Park Lower Mid Section – Almost Four Years After

Restoration

Niokaska Creek at Gulley Park Lower Section Before Restoration

Infrastructure

Trail Encroachment

Channel Incision

Niokaska Creek at Gulley Park One Week After Restoration

Niokaska Creek at Gulley Park One Year After Restoration

Niokaska Creek at Gulley Park Lower Section Four Years After Restoration

March 18, 2008 Storm Event Before Restoration

After Restoration August 23, 2008 Storm Event

Three Days After Major Construction Completed

Receding Flow After Storm Event

After Restoration August 23, 2008 Storm Event

Niokaska Creek at Sweetbriar Park High Pressure Waterline Before Restoration

Infrastructure Constraints

36” – 200 psi water main Check Dam

Niokaska Creek at Sweetbriar Park High Pressure Waterline After Restoration

Cross-vane used to bring stream

down from water line elevation

Niokaska Creek at Sweetbriar Park Waterline Section Before Restoration

Infrastructure Constraints

Adjacent Structures

36” – 200 psi water main

Niokaska Creek at Sweetbriar Park Waterline Section After Restoration

Infrastructure Constraints

Adjacent Structures

Niokaska Creek at Sweetbriar Park Waterline Section Before Restoration

Niokaska Creek at Sweetbriar Park Waterline Section Before Restoration

Niokaska Creek at Sweetbriar Park

Post Construction Flooding

Mullins Branch

Upstream Section – Before Restoration Infrastructure Constraints

18” – Sewer Line

Triple Box Culvert

Mullins Branch

Upstream Section – Before Restoration Infrastructure Constraints

18” – Sewer Line

Encased and finished with

native sandstone

Mullins Branch

Upstream Section – After Restoration

18” – Sewer Line

Mullins Branch

Middle Section – Before Restoration Infrastructure Constraints

Fixed width under bridge

Mullins Branch

Middle Section – After Restoration Infrastructure Constraints

Conclusions

Some general reminders Design for bankfull but expect and

be prepared for the “big one”

Plan for repairs (see above)

Establish a contingency fund (see above)

Get your permits Local, State, Federal

Carefully evaluate site constraints

Select experienced contractors

Plant and irrigate the site Better project performance Improves habitat Improves aesthetics

Develop a PR plan

Watershed Conservation Resource Center Thanks to Our Project Partners

Arkansas Natural Resources Commission

City of Fayetteville

University of Arkansas

U.S EPA Region VI

Questions? Matthew Van Eps, PE

Watershed Conservation Resource Center

vaneps@watershedconservation.org

(501) 352-7294