This document discusses the development of tools to help manage and assess hydromodification, which is the alteration of natural flow patterns caused by increased impervious surfaces like roads and buildings. It summarizes previous related studies and outlines the major tasks of the current project, which include developing protocols to classify stream susceptibility, monitoring impacts, predictive models, and management tools. The expected products are screening and assessment tools to evaluate hydromodification risks and impacts, as well as mitigation tools to guide management strategies based on stream and catchment conditions and the level of development.

1. Developing Tools for Hydromodification Management and Assessment Eric Stein S. Ca. Coastal Water Research Project (SCCWRP) [email_address]

2. Today’s Presentation Project Overview General Study Approach Tool development Expected Products Status

3. Effect of Increased Impervious Cover Hydromodification

4. Effects of Hydromodification

5. Regional Issue  Regional Approach Relationship between increased impervious cover and stream stability is a regional concern Build on previous work: Stormwater Monitoring Coalition (SMC) Santa Clara County Contra Costa County

6. Prior Study Approaches 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 Modeling studies in SF Bay area counties Long-term hydrologic simulations Risk-based modeling

7. 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 ≈ 5% 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 SCCWRP Technical Reports #450 and #475 – www.sccwrp.org

8. Conclusions of Past Studies Empirical Analysis (S. Ca.)

9. Conclusions of Past Studies Empirical Analysis (S. Ca.) Logistic Regression (Modeling) (S.F. Bay Area)

10. Current Study Joint project between SCCWRP and Colorado State Univ. Based on results of 2005 workshop Funded by Proposition 50 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?

11. 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

12. Preliminary Study Sites Data to support : - Development of screening tool - Calibration of predictive models - Development of standard monitoring protocols

13. Expected 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

14. Screening Tool Not all streams are the same Level of concern & appropriate management strategy will differ based on: Condition of stream Condition of catchment Anticipated change in land use/runoff Existing control/management measures Proposed management measures Tool to help prioritize level of effort/attention Checklist, decision tree, etc.

15. Elements of Screening Tool Intrinsic Channel Properties Catchment Characteristics Existing Infrastructure

16. Different Goals for Different Stages Protect manage runoff buffer stream Restore stabilize recontour Manage for New Condition alternate stream type

17. Modeling Tool Channels are dynamic, vary over multiple time scales Goal is to understand long-term “equilibrium” condition after proposed land use change Ultimate target period beyond most typical monitoring Need to “translate” model results into simple to use tools for planners & managers Nomographs, plots, tables

18. Working Hypotheses Urbanization & increased imperviousness shift the natural delivery of water and sediment to a water course, increasing the risk of incision, widening, and general instability  change in channel form Class III Class II Class IV Class V Class I Class V Class II Class III Class I Class Ia Class IV

19. Interaction of Models

20. Mitigation Tool Management response will vary based on: Existing channel condition Proposed change in land use, runoff Need to select appropriate management actions: On site runoff control Stream channel buffering Floodplain restoration Structural control Manage for new “equalibrium” condition Decision tools for managers, planners, etc Fact sheets, decision trees, tables

21. What is Appropriate Management Response? Hasley Canyon Wash

22. Next Steps Site selection completed Field data collection – Summer 2007 Produce draft protocols & monitoring recs. – Fall 2007 Produce draft screening tools – Spring 2008 Modeling – 2009 Final Products – Winter 2010

23. Questions? Eric Stein 714-755-3233 [email_address]