Effect of Increased Impervious Cover

1. Hydromodification Effect of Increased Impervious Cover

2. Regional Issue  Regional Approach • Relationship between increased impervious cover and stream stability is a regional concern • Stormwater Monitoring Coalition (SMC) decided to address this issue under their research agenda • Los Angeles County DPW is lead on first phase of hydromodifcation assessment project

3. Prior Study - Approach • Compare historic and contemporary channel shape and size to changes in impervious cover • Use relationship between changes in channel stability and changes in impervious cover to determine expected responses in S. Ca. streams • 10 sites across S. Ca. region • 7 sites – developing • 3 sites – control

4. Major Conclusions • Southern Ca. streams appear to be more sensitive to changes in impervious cover than streams in other areas of the country • Estimated threshold of response ≈ 2-3% TIMP • All streams studied are adjusting to flow conditions on an annual basis • All streams undergo constant change and adjustment • Rate of change differs between natural and developed areas • Management approaches will differ depending on stream type, drainage area and amount of impervious cover

5. Next Steps • Workshop to coordinate w/ other hydromodification studies • October 2005 workshop  Technical Report #475 • Additional data collection and empirical analysis • Establishment of ongoing (sentinel) monitoring sites • Development of predictive model(s) • Development of management tools

6. Prop 50 Proposal - Goals Joint proposal between SCCWRP and CSU (Brian Bledsoe) • Which streams are at the greatest risk of effects of hydromodification? • What are the anticipated effects in terms of increased erosion, sedimentation, or habitat loss, associated with increases in impervious cover? • What are some potential management measures that could be implemented to offset hydromodification effects?

7. Prop 50 Proposal – Major Tasks • Develop protocols for mapping and classification • Susceptibility evaluation • Develop protocols for monitoring and assessment • Additional data for model development • Develop and calibrate predictive models • Develop management tools

8. Prop 50 Proposal - Products • Screening tool – evaluate whether or not a project is likely to be of concern for hydromodification • Checklists • Effects tools –evaluate the expected magnitude or intensity of effect • Models, decision tree, nomograph or plots • Mitigation tools –guide recommended mitigation and management measures. • fact sheets, design criteria, sizing standards

9. Prop 50 – Proposed Schedule Task 1: Project Management Task 2: Protocols for mapping and classification Summer 2007 Task 3: Protocols for regional monitoring/assessment Winter 2008 Task 4/5: Screening tools Fall 2008 Task 4/5: Dynamic simulation model Summer 2009 Task 4/5: Management tools Fall 2009 Winter 2010 Task 6: Report preparation & Outreach

10. Opportunities for Collaboration • Co-location of field sites • Joint Technical Advisory Committee • Coordination on tool development

11. Questions? NOTE NEW PHONE NUMBER Eric Stein 714-755-3233 erics@sccwrp.org www.sccwrp.org