Transcript Watershed Planning - Chesapeake Stormwater Network

Changing Course:
Streambed Restoration and
Stabilization
APWA Webcast
January 19, 2006
Session Agenda
A. Setting realistic expectations
B. How urban streams work
C. Design considerations for urban stream repair
projects
D. Sources of funding for local stream repair
projects
Manual 4 Urban Stream Repair Practices
First manual
specifically
focusing on urban
streams
33 different repair
practices
Available from
www.cwp.org
Setting Realistic Expectations
1. The ICM and stream repair
2. Range of stream repair objectives
Impervious Cover Sets Expectations for Urban Streams
Rock Creek
BIBI = 48
(excellent)
Biological Integrity of Puget Lowland Streams
Stream Health (BIBI score)
50
40
Sensitive Impacted
Non-supporting
Urban
drnge.
30
20
10
Data from Sarah Morley, Univ. of WA
1997-1999
0
0
10
20
30
40
50
60
Urban Development (TIA in watershed)
70
Biological Integrity of Puget Lowland Streams
Stream Health (BIBI score)
50
40
30
20
10
0
0
10
20
30
40
50
Urban Development (TIA in watershed)
60
70
Management Strategies
Stream Health (BIBI score)
50
Protection
40
30
Rehabilitation
20
Stewardship
10
0
0
Source Booth 2004
10
20
30
40
50
Urban Development (TIA in watershed)
60
70
Numerous objectives for stream repair
1.
2.
3.
4.
5.
6.
7.
8.
9.
Cleanup Stream Corridor
Naturalize Stream Corridor
Protect Threatened Infrastructure
Prevent Bank Erosion
Expand/Reconnect Stream Network
Increase Fish Passage
Improve Fisheries Habitat
Achieve Natural (Stable) Channel Design
Recover Aquatic Diversity & Function
The public has many perceptions on what’s a good urban stream
How Urban Streams Work
1. Basic stream geomorphology
2. 3 phases of urban channel evolution
3. Effects on stream biota
Lane’s Balance
Phase 1: Initial Construction
More sediment load
Increased discharge
Temporary aggradation
Or live in
this soup?
Phase 1
Aggradation
Caused by
Upstream
Construction
Stream Symptoms During Aggradation
1.
2.
3.
4.
5.
Mid-channel bars
Embedded riffles
Siltation in pools
Accretion on point bars
Deposition in the overbank zone
Phase 2: Active Channel Adjustment
Much Higher Discharge
Increased Sediment (banks)
Degradation/channel enlargement
Example of
Extreme
Channel
Incision
aka
Downcutting
Symptoms of active channel enlargement
1. Cut face on bar forms
2. Headcutting and knickpoint
migration
3. Suspended armor layer in bank
4. Terrace cut through older bar
material
5. Exposed sanitary or storm sewers
10
9
8
H is toric c ros s -s ec tion
H is to r ic S e c tio n
E levatio n (ft-msl)
7
C u r r e n t S e c tio n
6
B a n kf u ll D e p th
U ltim a te S e c tio n ?
5
4
C urrent c ros s -s ec tion
3
2
U ltim ate c ros s -s ec tion ?
1
0
0
5
10
15
20
25
30
35
C ro ss S ectio n S tatio n s (ft) - L o o kin g D o w n stream
40
45
Channel Enlargement As a Function of
Impervious Cover
Why 2-year peak discharge doesn’t work
Traditional 2 year peak discharge control does not
reduce frequency of bankfull and sub-bankfull flows
that cause erosion
Indeed, it may actually worsen conditions since it
increases the duration by which they occur
Conventional 2 Year Peak Flow Control Approach
24 Hour ED of 1-year storm
One-year storm ranges from 1.5 to 2.5 inches of
rainfall
Entire volume stored and released with average 24
hour detention
12 hour ED for trout streams (warming)
Reduces velocities below critical erosive levels
Adopted or proposed in MD, NY, GA, PA, NY, MN
Phase 2:
Active Channel Enlargement
Continued channel incision/entrenchment
Loss of habitat structure
Easter Lk. Outlet,
Federal Way, WA
Symptoms of Active Channel Widening
1. Falling/leaning trees
2. Scour on both banks through
riffle
3. Exposed tree roots
4. Fracture lines along top of bank
5. Exposed infrastructure
Phase 3:
Eventual Adjustment to More Stable
Channel Dimensions:
2 to 5 Decades After Subwatershed Buildout
Case Study: Has this stream adjusted yet?
Symptoms of Channel (re?)stabilization
1. Water reaches the toe of each bank
2. Moss on rocks or extending down to
the bottom of the bank
3. Banks are stable
4. Erosion is slight and limited to
meander bends
Effects on stream biota
Stream warming
Channel enlargement
Habitat degradation
Food chain effects
Declining baseflow
Possible toxicity
Fish barriers
Loss of spawning habitat
Urban Stream Repair
1. Subwatershed restoration approach
2. Review of stream repair practices
3. Design context for urban stream repair
4. Unique urban stream design constraints
Subwatershed restoration approach
1. Design stream repairs at
the reach scale in the
context of the larger
subwatershed
2. Systematic assessment
of repair potential across
subwatershed
3. Integrate w/other
restoration practices
Stream repair is only one of several
restoration practices
 Stormwater
retrofits
 Discharge
Prevention
 Riparian
restoration
 Source control
 Municipal
practices
 Watershed
forestry
Should be part of an overall plan (& reserved for impacted
urban streams)
http://www.saveourstreams.org
C1 and C2
Stream Cleanup and Adoption Practices
Stream Repair Practices
Streambank Stabilization
Flow Deflection
Grade Control
Stream Repair Practices (cont.)
Habitat Enhancement
Fish Passage
Flow Diversion
The design context for urban
stream repair
←←
←
REACH
Current IC: 22%
IC at Buildout: 30%
Time to Subwatershed Buildout: 25 years
Pond Retrofit Potential: High
Case Study: How might the following upstream factors
influence restoration?
B. Important Project Reach Factors
1. Channel
confinement
2. Longitudinal
profile
3. Channel crosssection
4. Streambed
5. Streambanks
6. Water quality
Urban Channel Confinement – Not enough room in the
Floodplain to allow for natural sinuosity. Energy must be
dissipated vertically rather than laterally. The Harman Rule: Need
6.0 Thewidth
Urban
Corridor
at least 3.5 X bankfull
to Stream
even think
about sinuousity
Rosgen classifications and methods need to be
carefully adapted for use in urban streams.
Source: UCMT, 2004
2.0 Longitudinal Stream Gradient Critical
Upward Migration
of Knickpoints
Grade Control Key In Urban
Streams
•Maintain streambed elevation
•Prevent/reverse channel incision
3.0 The Current and Future Stream Cross-section will
seldom be the same
Forest
Turf
Stream Channel Geometry Influenced by Urban
Riparian Conditions
4.0 The Streambank under Assault
5.0 The Streambed
6.0 Water Quality
Make sure to consult w/ local fishery biologists
C. Downstream Factors are also critical
An Interrupted Stream
Maidens Choice Subwatershed
Baltimore, MD
Loss of Riparian Buffer Continuity: Hospital Branch, TN
Partial and Final
Barriers to Fish
Migration in the
Anacostia
Watershed
Most local stream repair projects
 Are funded from local capital
budgets
 To protect threatened
infrastructure or property
 Are “band-aids” that solve the
symptoms but not the underlying
problem
More funding is available when:
 Innovative stream repair projects are



demonstrated
Is a part of a larger watershed plan
Local watershed groups support it
Partners are involved to leverage
resources
Sources of Funding for Local Stream
Repair Projects
1. Fish and Wildlife Service
2. National Fish And Wildlife
Foundation (NFWF)
3. EPA 319 Grant Program
4. Salmon Recovery Fund
5. State Highway Mitigation
Other Sources
1.
2.
3.
4.
State Natural Resource Agencies
Trout Unlimited
U.S. Army Corps of Engineers
Local and State Permit
Conditions
5. Stormwater mitigation fees