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