stream restoration in the urban environment
TRANSCRIPT
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
(501) 352-7294