Study to quantify runoff coefficients associated with turf replacement BMPs

SCCWRP and the County of San Diego have begun working to measure how much rainfall and dry-weather irrigation soaks into the ground vs. runs off the land at sites where spray-irrigated turf has been
replaced with drip irrigation and drought-tolerant landscaping.

The study, which will kick off with field testing in March, is a follow-up to a recently completed San Diego County study that found that turf replacement projects – a type of stormwater BMP – can successfully eliminate all irrigation runoff during dry weather, as well as all rainfall during an estimated 85% of all storms.

Stormwater managers need to know the ratio of water that soaks into the ground vs. runs off the land – known as the runoff coefficient – as they’re modeling how much rainfall and irrigation is expected to be retained by different land-use types. Although managers typically take this information from reference textbooks and practitioner manuals, there are no published values for turf replacement projects because it is a novel BMP type.

Enabling this study will be a rainfall generator custom-built by SCCWRP that simulates relevant, controlled rainfall patterns, while eliminating much of the variability that surrounds real-world rainfall and runoff events.

The runoff coefficients that researchers derive will be used to help improve a computer model developed by the County to prioritize applications within its Waterscape Rebate Program for areas where turf replacement projects are likely to maximize runoff water-quality benefits.