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HYDROMODIFICATION: HYDROMODIFICATION: AN INTRODUCTION AND OVERVIEWAN 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• 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 watershed2. Build near the river3. River floods4. Call for help: “somebody do something!”
A hero arose…
In the hour of need…
Our tools…
and the scale of our projectsrapidly 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
The era of multi-objective watershed mgmt
In response to these problems, the regulatory climate has changed dramatically, and we have entered
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 management2. Wildlife habitat3. Urban Runoff Water Quality
Despite our flood control and water quality efforts, channel problems continued….
Channel incision
Downstream deposition
DISCUSSION TOPICS
• HISTORICAL PERSPECTIVE• HYDROMOD PROCESSES• MANAGEMENT STRATEGIES• CONCLUSIONS
Urbanization Direct Hydrologic Impacts
• Increased runoff volume• Increased peak flow rates• Reduced time lag to peak flow• Increased duration of high flow• Increased frequency of flow events
runoff
infiltration
precipitation
Runoff Processes
Hydrograph Modification Impacts
Run
off
Time
Pre-Development
Urbanization tends to increase stormwater runoff:
peak flows
volume
frequency
Post-Development
• 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
• Increased Channel network complexity• Increased channel “efficiency”
Historical Channel Modification associated with development
Stevens Creek,
ca 1870 and 1899
ca 1870 1899
Expansion of channel incision: creation of new first order channels
Urbanization Hydrologic Impacts: Variability(all watersheds and streams are not created equal)
• 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
• HISTORICAL PERSPECTIVE• HYDROMOD PROCESSES• MANAGEMENT STRATEGIES• CONCLUSIONS
Management Strategies
• 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. Flood hazard management2. Wildlife habitat3. Urban Runoff Water Quality4. Downstream impacts from
increased runoff (hydro- modification)
Management Strategies
• 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
• 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
Wetland/wildlife Habitat
•Expanding our flood detention facilities to include hydromod: -they will have to be considerably larger
-outlet structures will be more complex
-allows regional mgmt
Water Quality Management•Wetland treatment ponds
Management Strategies
• 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
• HISTORICAL PERSPECTIVE• HYDROMOD PROCESSES• MANAGEMENT STRATEGIES• CONCLUSIONS
Concluding thoughts• 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 long-
term experience• The regulatory process is ahead of administration• Long-term Performance/Maintenance?
In Response:
• Monitoring is important• Flexibility in technology, regulation,
administration• Expect rapid evolution in the field:
“Adaptive Management”
• You learn about natural systems by field observation and data collection (NOT just sitting behind a computer screen or a book)
Field Data Collection
Field Data Collection
• Ignore the discomforts
Bring the kids
Be thorough
The importance of field work: We learn more from observation than from computer models
• You learn how to build projects by trying things out and learning from your mistakes and successes
Project Design and Implementation
• 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