Hydromodification Controls

Eroded creek filled with sediment (Photo by Program staff)

When land is covered with buildings and pavement, runoff enters creeks at higher rates and volumes, resulting in channel erosion, flooding and habitat loss.  These changes in runoff characteristics are known as hydromodification.  Hydromodification management measures are detention and/or infiltration facilities that are constructed with special discharge structures to match pre-project runoff patterns.

Hydromodification controls help prevent worsening of creek channel erosion problems from new development or redevelopment projects.  Hydromodification management requirements are different from flood control requirements.

New development and redevelopment projects that create or replace at least one acre of impervious surface, increase impervious surface area above the pre-project condition, and are in a susceptible area, are required to implement hydromodification management requirements.


SCVURPPP, along with the San Mateo and Alameda County stormwater programs, helped fund the development of the Bay Area Hydrology Model (BAHM), a tool for simulating pre- and post-project hydrology and automatically sizing flow control facilities to better manage hydromodification.  Clear Creek Solutions developed this model for the Bay Area, and SCVURPPP helped calibrate the model in Santa Clara Valley watersheds.  Click below to download the BAHM2013 tool.