HYDROMODIFICATION:
AN INTRODUCTION AND OVERVIEW
Presented by
Jeffrey Haltiner, Ph.D., P.E.
Philip Williams & Associates, Ltd.
San Francisco, CA
May2006
Hydromodification: An
Integrated Element of
Stormwater Management
DISCUSSION TOPICS
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HISTORICAL PERSPECTIVE
HYDROMOD PROCESSES
MANAGEMENT STRATEGIES
CONCLUSIONS
HISTORICAL CHANGES IN
CALIFORNIA STREAMS:
subtitled: “whither goest Willow
Creek
“How did we get here and whose fault is it anyway?”
Native American Life in
California
An “adaptive” lifestyle
Dry Season
Wet Season
Arrival of the Spanish… and their cows
All of this occurred before the
invention of the modern “low
impact” cow
California in the 20th Century
California in the 20th
Century: Urban and
suburban growth
Development sequence:
1. Develop the watershed
2. Build near the river
3. River floods
4. Call for help: “somebody do something!”
In the hour of need…
A hero arose…
Our tools…
and the scale of our projects
rapidly expanded
But along the way,
our vision of rivers
and streams
Began to get lost
As did our natural connection with
streams
We began to get some bad press
And our
image
changed
for the
worse
In response to
these problems, the
regulatory climate
has changed
dramatically, and
we have entered
The era of multiobjective
watershed mgmt
Regulatory Framework
Flood management
– FEMA
– Local Flood Control Districts
Habitat protection
– US Fish & Wildlife Service (Section 7)
– CA Department of Fish & Game (Section 1601)
Water Quality
– Federal Clean Water Act (US EPA)
– Regional Water Quality Control Boards (RWQCBs)
In response to the regulatory
requirements, we developed methods
to address:
1. Flood hazard management
2. Wildlife habitat
3. Urban Runoff Water Quality
Despite our flood control and water
quality efforts, channel problems
continued….
Channel incision
Downstream deposition
DISCUSSION TOPICS
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HISTORICAL PERSPECTIVE
HYDROMOD PROCESSES
MANAGEMENT STRATEGIES
CONCLUSIONS
Urbanization Direct Hydrologic
Impacts
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Increased runoff volume
Increased peak flow rates
Reduced time lag to peak flow
Increased duration of high flow
Increased frequency of flow events
Runoff Processes
precipitation
runoff
infiltration
Hydrograph Modification Impacts
Urbanization tends to
increase stormwater
runoff:
Pre-Development
 volume
Post-Development
Runoff
 peak flows
 frequency
Time
• While we understand
the basic effects of
urbanization, the
detailed processes
are v. complex
• We use simple tools
to characterize these
impacts.
Scientific/modeling overview:
Rainfall-runoff processes/modeling
Rainfall-runoff:
spatial and
vertical
complexity
Scientific/modeling overview:
Stream channel processes
Basic concept is that
altered hydrology
results in channel
erosion
Very difficult to predict
the “threshold” for
channel response
Urbanization Indirect
Hydrologic Impacts
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Increased Channel network complexity
Increased channel “efficiency”
Historical Channel Modification
associated with development
ca 1870
Stevens Creek,
ca 1870
and 1899
1899
Expansion of channel incision:
creation of new first order channels
Urbanization Hydrologic
Impacts: Variability
(all watersheds and streams are not
created equal)
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Soil characteristics
Cover (vegetation, duff layer etc)
Channel characteristics (bed material, slope
etc)
Sensitivity to hydromod varies greatly
Watershed sensitivity to
flow: Central coast example
Stream Channel sensitivity to flow changes:
Stream response depends on morphology
DISCUSSION TOPICS
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•
•
•
HISTORICAL PERSPECTIVE
HYDROMOD PROCESSES
MANAGEMENT STRATEGIES
CONCLUSIONS
Management Strategies
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•
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Regulatory compliance/Implementation
Integrating hydromod with other hydrologic
project elements
Development location/footprint
Managing site runoff
Channel management
Regulatory Framework
• Flood management
• Habitat protection
• Water Quality
• Hydrograph Modification Management
– New NPDES permit requirements (RWQCBs)
– How should it be regulated? Who should lead the
regulatory side?
– Which agency should manage this?
In developing hydrologic strategies in
urbanizing areas, we now need to
integrate four key elements:
1.
2.
3.
4.
Flood hazard management
Wildlife habitat
Urban Runoff Water Quality
Downstream impacts from
increased runoff (hydromodification)
Management Strategies
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•
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Regulatory compliance
Integrating hydromod with other hydrologic
project elements
Development location/footprint
Managing site runoff
Channel management
Much of the urbanization
in the state has
already occurred
Much of the new
permitting will be on
small infill projects
and small to medium
developments at the
urban fringe.
Site design and layout has a major effect on the
stormwater runoff effects.
Mass site grading and extensive,
connected paving lead to large
increases in runoff rate and
volume.
-Maintain open space
-Maintain pervious soils
-Disconnect impervious areas
-Create pervious zones/buffers
Management Strategies
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Integrating hydromod with other hydrologic
project elements
Regulatory compliance
Development location/footprint
Managing site runoff
Channel management
Designing a
‘storage’ vs.
‘conveyance’
approach to
runoff
management
On-site/individual unit mgmt: Planter
Box
IMP Gallery
•Infiltration trench/
basin
•Vegetated swale
Detention facilities can be modified to include
hydromod
Park/permanent pond
•Expanding our flood
detention facilities to
include hydromod:
-they will have to be
considerably larger
-outlet structures will be
more complex
Wetland/wildlife Habitat
-allows regional mgmt
Water Quality Management
•Wetland treatment
ponds
Management Strategies
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Integrating hydromod with other hydrologic
project elements
Regulatory compliance/Implementation
Development location/footprint
Managing site runoff
Channel management
DOUGHERTY VALLEY: ALAMO
CREEK RESTORATION
EXCAVATION
OF A NEW
FLOODPLAIN
TERRACE
ALAMO CREEK AND RESTORED
FLOODPLAIN:
POST CONTSTRUCTION
DISCUSSION TOPICS
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HISTORICAL PERSPECTIVE
HYDROMOD PROCESSES
MANAGEMENT STRATEGIES
CONCLUSIONS
Concluding thoughts
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We are inheriting watersheds and streams with extensive
impacts
Hydromod management must be integrated with other
management elements
Hydromod management must be applicable to different
watershed locations
The regulatory process is ahead of technology; no longterm experience
The regulatory process is ahead of administration
Long-term Performance/Maintenance?
In Response:
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Monitoring is important
Flexibility in technology, regulation,
administration
Expect rapid evolution in the field:
“Adaptive Management”
Field Data Collection
• You learn about natural systems by field observation and data
collection (NOT just sitting behind a computer screen or a book)
Field Data Collection
•
The importance of
field work: We
learn more from
observation than
from computer
models
Ignore the discomforts
Bring the kids
Be thorough
Project Design and Implementation
• You learn how to build projects by trying things out and learning
from your mistakes and successes
• It is easier to criticize than to do!
• Be humble; there is a lot to learn
Hydro mod means urban: Get involved in the
community
Build Education into your projects
Share what you’ve learned
Teach the next generation too…
(they’ll be paying for your social security)
Hydromod
management is
poised at the
crossroads of
Technology and
Innovation