HYDROMODIFICATION: AN INTRODUCTION AND OVERVIEW

1. HYDROMODIFICATION: AN INTRODUCTION AND OVERVIEW • Presented by • Jeffrey Haltiner, Ph.D., P.E. • Philip Williams & Associates, Ltd. • San Francisco, CA • May2006

2. Hydromodification: An Integrated Element of Stormwater ManagementDISCUSSION TOPICS • HISTORICAL PERSPECTIVE • HYDROMOD PROCESSES • MANAGEMENT STRATEGIES • CONCLUSIONS

3. HISTORICAL CHANGES IN CALIFORNIA STREAMS:subtitled: “whither goest Willow Creek • “How did we get here and whose fault is it anyway?”

5. Native American Life in California

6. An “adaptive” lifestyle Dry Season Wet Season

8. Arrival of the Spanish… and their cows

9. All of this occurred before the invention of the modern “low impact” cow

11. California in the 20th Century

12. California in the 20th Century: Urban and suburban growth

13. Development sequence:1. Develop the watershed2. Build near the river3. River floods4. Call for help: “somebody do something!”

14. In the hour of need… A hero arose…

15. Our tools… and the scale of our projectsrapidly expanded

16. But along the way, our vision of rivers and streams

17. Began to get lost

18. As did our natural connection with streams

19. We began to get some bad press

20. And our image changed for the worse

22. In response to these problems, the regulatory climate has changed dramatically, and we have entered The era of multi-objective watershed mgmt

23. 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)

24. In response to the regulatory requirements, we developed methods to address: 1. Flood hazard management2. Wildlife habitat3. Urban Runoff Water Quality

25. Despite our flood control and water quality efforts, channel problems continued…. Channel incision Downstream deposition

26. DISCUSSION TOPICS • HISTORICAL PERSPECTIVE • HYDROMOD PROCESSES • MANAGEMENT STRATEGIES • CONCLUSIONS

27. 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

28. precipitation runoff infiltration Runoff Processes

29. Urbanization tends to increase stormwater runoff: • peak flows • volume • frequency Post-Development Hydrograph Modification Impacts Pre-Development Runoff Time

30. While we understand the basic effects of urbanization, the detailed processes are v. complex • We use simple tools to characterize these impacts.

31. Scientific/modeling overview:Rainfall-runoff processes/modeling • Rainfall-runoff: spatial and vertical complexity

32. 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

33. Urbanization Indirect Hydrologic Impacts • Increased Channel network complexity • Increased channel “efficiency”

34. Historical Channel Modification associated with development ca 1870 1899 Stevens Creek, ca 1870 and 1899

35. Expansion of channel incision: creation of new first order channels

36. 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

37. Watershed sensitivity to flow: Central coast example

38. Stream Channel sensitivity to flow changes: Stream response depends on morphology

39. DISCUSSION TOPICS • HISTORICAL PERSPECTIVE • HYDROMOD PROCESSES • MANAGEMENT STRATEGIES • CONCLUSIONS

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

41. 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?

42. 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)

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

44. 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.

45. 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

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

47. Designing a ‘storage’ vs. ‘conveyance’ approach to runoff management

48. On-site/individual unit mgmt: Planter Box

49. IMP Gallery • Infiltration trench/ • basin • Vegetated swale

50. 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