HYDROMODIFICATION: AN INTRODUCTION AND OVERVIEW

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HYDROMODIFICATION AN INTRODUCTION AND OVERVIEW

• Presented by
• Jeffrey Haltiner, Ph.D., P.E.
• Philip Williams Associates, Ltd.
• San Francisco, CA
• May2006

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Hydromodification An Integrated Element of
Stormwater ManagementDISCUSSION TOPICS

• HISTORICAL PERSPECTIVE
• HYDROMOD PROCESSES
• MANAGEMENT STRATEGIES
• CONCLUSIONS

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HISTORICAL CHANGES IN CALIFORNIA
STREAMSsubtitled whither goest Willow Creek

• How did we get here and whose fault is it
  anyway?

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Native American Life in California
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An adaptive lifestyle
Dry Season
Wet Season
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Arrival of the Spanish and their cows
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All of this occurred before the invention of the
modern low impact cow
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California in the 20th Century
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California in the 20th Century Urban and
suburban growth
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Development sequence1. Develop the watershed2.
Build near the river3. River floods4. Call
for help somebody do something!
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In the hour of need
A hero arose
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Our tools
and the scale of our projectsrapidly expanded
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But along the way, our vision of rivers and
streams
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Began to get lost
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As did our natural connection with streams
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We began to get some bad press
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And our image changed for the worse
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The era of multi-objective watershed mgmt
In response to these problems, the regulatory
climate has changed dramatically, and we have
entered
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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)

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In response to the regulatory requirements, we
developed methods to address
1. Flood hazard management2. Wildlife
habitat3. Urban Runoff Water Quality
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Despite our flood control and water quality
efforts, channel problems continued.
Channel incision
Downstream deposition
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DISCUSSION TOPICS

• HISTORICAL PERSPECTIVE
• HYDROMOD PROCESSES
• MANAGEMENT STRATEGIES
• CONCLUSIONS

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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

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Runoff Processes
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Hydrograph Modification Impacts
Pre-Development
Runoff
Time
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• While we understand the basic effects of
  urbanization, the detailed processes are v.
  complex
• We use simple tools to characterize these
  impacts.

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Scientific/modeling overviewRainfall-runoff
processes/modeling

• Rainfall-runoff spatial and vertical complexity

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Scientific/modeling overviewStream channel
processes

• Basic concept is that altered hydrology results
  in channel erosion
• Very difficult to predict the threshold for
  channel response

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Urbanization Indirect Hydrologic Impacts

• Increased Channel network complexity
• Increased channel efficiency

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Historical Channel Modification associated with
development
ca 1870
1899
Stevens Creek, ca 1870 and 1899
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Expansion of channel incision creation of new
first order channels
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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

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Watershed sensitivity to flow Central coast
example
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Stream Channel sensitivity to flow changes
Stream response depends on morphology
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DISCUSSION TOPICS

• HISTORICAL PERSPECTIVE
• HYDROMOD PROCESSES
• MANAGEMENT STRATEGIES
• CONCLUSIONS

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Management Strategies

• Regulatory compliance/Implementation
• Integrating hydromod with other hydrologic
  project elements
• Development location/footprint
• Managing site runoff
• Channel management

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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?

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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)
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Management Strategies

• Regulatory compliance
• Integrating hydromod with other hydrologic
  project elements
• Development location/footprint
• Managing site runoff
• Channel management

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• 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.

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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
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Management Strategies

• Integrating hydromod with other hydrologic
  project elements
• Regulatory compliance
• Development location/footprint
• Managing site runoff
• Channel management

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Designing a storage vs. conveyance approach
to runoff management
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On-site/individual unit mgmt Planter Box

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IMP Gallery

• Infiltration trench/
• basin
• Vegetated swale

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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-allows regional mgmt

Wetland/wildlife Habitat
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Water Quality Management

• Wetland treatment ponds

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Management Strategies

• Integrating hydromod with other hydrologic
  project elements
• Regulatory compliance/Implementation
• Development location/footprint
• Managing site runoff
• Channel management

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DOUGHERTY VALLEY ALAMO CREEK RESTORATION
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EXCAVATION OF A NEW FLOODPLAIN TERRACE
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ALAMO CREEK AND RESTORED FLOODPLAINPOST
CONTSTRUCTION
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DISCUSSION TOPICS

• HISTORICAL PERSPECTIVE
• HYDROMOD PROCESSES
• MANAGEMENT STRATEGIES
• CONCLUSIONS

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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?

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In Response

• Monitoring is important
• Flexibility in technology, regulation,
  administration
• Expect rapid evolution in the field Adaptive
  Management

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Field Data Collection

• You learn about natural systems by field
  observation and data collection (NOT just sitting
  behind a computer screen or a book)

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Field Data Collection

• Ignore the discomforts

The importance of field work We learn more from
observation than from computer models
Bring the kids
Be thorough
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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

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Hydro mod means urban Get involved in the
community
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Build Education into your projects
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Share what youve learned
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Teach the next generation too(theyll be paying
for your social security)
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Hydromod management is poised at the crossroads
of Technology and Innovation
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