Doug Beyerlein, P.E., Clear Creek Solutions, Inc. The Bay Area Hydrology Model: A Tool for Analyzing Hydromodification Effects of Development Projects and Sizing Solutions Jill C. Bicknell, P.E., EOA , Inc. Santa Clara Valley Urban Runoff Program Doug Beyerlein, P.E., Clear Creek Solutions, Inc.

The Bay Area Hydrology Model: A Tool for Analyzing Hydromodification Effects of Development Projects and Sizing Solutions This presentation given by Jill Bicknell and Doug Beyerlein at the September 2006 CASQA Conference in Sacramento, CA.

Acknowledgements Funding Agencies Arleen Feng (ACCWP) Santa Clara Valley Urban Runoff Pollution Prevention Program (SCVURPPP) Alameda Countywide Clean Water Program (ACCWP) San Mateo Countywide Stormwater Pollution Prevention Program (STOPPP) Arleen Feng (ACCWP) Tony Donigian (Aqua Terra Consultants) Gary Palhegyi (GeoSyntec Consultants)

Presentation Overview Background / Permit Requirements Technical Approach to Control of Hydromodification Design Challenges / Need for BAHM Overview of the BAHM BAHM Parameter Development BAHM Application BAHM = Bay Area Hydrology Model

What is Hydromodification? Change in the runoff hydrograph (flow pattern) from an area due to development Impacts of land development: Increase in impervious surface Decrease in amount of vegetation Grading and compaction of soils Construction of drainage facilities

What is Hydromodification? (continued) Effects of land development on the site runoff hydrograph: Less infiltration / evapotranspiration More surface runoff (increased volume) Runoff leaves the site faster (increased peak flows) Runoff occurs more often (increased duration) Runoff conveyed directly to creek (increased connectivity)

Hydromodification Control Requirements SF Bay Area Phase 1 MS4 Permits Permit Provision C.3.f.i.: Increases in runoff peak flow, volume, and duration shall be managed for all Group 1 Projects*, where such increased flow and/or volume can cause increased erosion of creek beds and banks… * Group 1 = > 1 acre impervious surface

Hydromodification Control Requirements Permit Provision C.3.f.i. (continued): Post-project runoff shall not exceed estimated pre-project rates and/or durations, where the increased storm water discharge rates and durations will result in increased potential for erosion… Must develop and implement Hydro-Modification Management Plans (HMPs)

Hydromodification Control Requirements Permit Provision C.3.f.ii. (Exemptions): Projects that discharge to tidal area, channel continuously hardened to the Bay, or directly to the Bay Projects that are “infill projects” in “highly developed watersheds” Other projects where potential for increased erosion is minimal (e.g., no increase in impervious area)

Stable stream, bed close to old tree Segment 5 Stable stream, bed close to old tree

Segment 4 Channel incision on Yerba Buena Creek

Undermining outfall protection structure Segment 1 Undermining outfall protection structure

Pre- and post-project runoff characteristics All Events Flood Frequency Flow Duration Critical flow (Qc=15 cfs) 2-year Frequency of events and duration

Control Strategies Peak flow control - not effective for erosion control (low flows matter) Single event/design storm approaches – not adequate hydromod control Flow duration control - recommended Maintain magnitude and duration of post-project flows same as pre-project Considers multi-year discharge record Site design (LID) measures – effective in reducing flow, use to supplement flow duration control facility

Flow Duration Histograms

Flow Duration Curve Matching

Range of Storms to Manage (Set of Design Storms) Qc to the 10-year event

Tale of Five HMPs Santa Clara Valley Contra Costa County Submitted Final HMP Report April 2005 RWQCB adopted July 2005 Contra Costa County Submitted Final HMP May 2005 RWQCB adopted July 2006 San Mateo & Alameda Counties, Fairfield-Suisun Submitted final HMPs, under review by RWQCB Adopt December 2006?

Performance Criteria Applicable projects with on-site flow controls that are designed to provide flow duration control to the pre-project condition are considered to comply with the HMP. Flow duration controls shall be designed to match pre- and post-project flow rates and durations from 10% of the pre-project 2-year peak flow to the pre-project 10-year peak flow.

On-Site Options Use site design techniques to reduce runoff flow and volume Decrease impervious surface area Disconnect impervious areas Promote infiltration Select treatment BMPs that reduce volume swales, detention areas, bioretention, green roofs

On-Site Options, continued Construct flow control structures Retention/detention basins Underground vaults/tanks Combine flow control with flood control and/or treatment facilities Examples: detention basin, wet pond, constructed wetlands

* Schematic Flow Duration Control Pond Overflow provision for peak events (storage may also be increased to meet flood control requirements) Inflows: site runoff after reductions from site design, infiltration or other retention measures C D A E - released at maximum discharge rate in pipe Dead storage (optional) Discharge to stream Bottom infiltration where applicable * B Point of Compliance: drainage point for comparing post-project and pre-project Flow Duration curves Legend: A) outlet pipe riser; B) low flow orifice; C) intermediate orifice (1 shown); D) weir notch (V-type shown); E) freeboard above riser (typically 1 foot). Schematic Flow Duration Control Pond

Integrating Flow Duration Control (FDC) with Other BMPs Urban Runoff FDC Basin Bio-infiltration Swale FDC Basin Stream FDC Vault Bio-infiltration Swale On-Site BMPs LID

Process for Evaluating Flow Control Requirements Hydrologic Analysis Generate pre- vs. post-project flow duration curves using hydrologic model Continuous simulation required Available models: Corps of Engineers’ HEC-HMS EPA HSPF EPA SWMM Western Washington Hydrology Model

Design Challenges Challenge #1: Flow duration control design Requires use of continuous simulation hydrologic model Use of these models is data intensive and time consuming Lack of knowledge and experience Challenge #2: Integrating flow controls with site design and treatment controls How to estimate flow reduction benefits of other BMPs How to estimate treatment capability of flow control facility

BAHM based on WWHM BAHM (Bay Area Hydrology Model) uses the EPA HSPF computational engine and WWHM (Western Washington Hydrology Model) software platform. BAHM hydrology parameter values are derived from locally calibrated watersheds.

WWHM Developed for the Washington State Department of Ecology. Used in the 19 counties of Western Washington.

BAHM Designed for the San Francisco Bay Area Alameda County Santa Clara County San Mateo County

BAHM Components user-friendly graphical interface automatically loads appropriate parameter values and meteorological data based on project location uses long-term (30+ year) local precip records and scales precip based on ratio of project site MAP and precip gage MAP

BAHM Graphical interface: Project Site

BAHM Graphical interface: Pre-Project Land Use Based on soil, vegetation, land slope, impervious area

BAHM Graphical interface: Project Land Use Based on soil, vegetation, land slope, impervious area

BAHM Graphical interface: HMP Facility Pond, tank, vault, gravel trench bed, bioretention

BAHM Graphical interface: Runoff Analysis AutoPond optimizes (minimizes) pond dimensions to meet HMP flow duration criteria

BAHM Calibration of local hydrologic parameter values Castro Valley Creek watershed Alameda Creek watershed

BAHM Comparison of simulated and observed Castro Valley Creek streamflow

BAHM Comparison of simulated and observed Alameda Creek streamflow

WWHM Application Examples Commercial site: Costco store, Woodinville, WA (14.38 acres)

WWHM Application Examples Commercial site: Costco store, Woodinville, WA (6 acre-feet of underground storage)

WWHM Application Examples Planned community: Snoqualmie Ridge, King County, WA (1,343 acres)

WWHM Application Examples Planned community: Snoqualmie Ridge, King County, WA (10 stormwater ponds ranging in size from 2 to 20 acre-feet)

Conclusion BAHM will facilitate compliance with HMP and design of flow control facilities in the Bay Area by providing: An easier, standardized way to do continuous simulation modeling A means to compute flow control benefits of site design/LID and treatment measures Standardized reporting to assist municipal staff in design review

Click on “New and Redevelopment Related Products and Reports” For More Information... Visit our website at: www.SCVURPPP.org Click on “New and Redevelopment Related Products and Reports” Work products will be included on this site. Currently the work plan and HMP workplan are available for downloading. That’s all, folks.