Methodologies for Valuing Stormwater Retained for MS4 Permit Compliance
More and more, stormwater managers tasked with complying with municipal separate storm sewer system (MS4) pollutant treatment and hydromodification control requirements are using watershed based approaches to select optimum mixtures of practices and facilities that retain stormwater. An element of optimization is determining the mixture of best practices and facilities—and the scale of implementation-- that maximizes benefits achieved relative to cost expended.
The stormwater management literature suggests many different benefits that can be realized through increased stormwater retention, such as receiving water quality improvement and water supply augmentation; nearly 30 different benefits can be found in the literature. However, benefits accrue in a variable nature because of great diversity in environmental conditions across California watersheds that affect stormwater retention, and because of highly variable existing stormwater management infrastructure conditions.
A consistent approach to identifying key benefits and monetizing those benefits is needed in order to assist in stormwater infrastructure prioritization, and in creating a “value” for stormwater retained. This presentation will provide a review of stormwater retention benefits achieved through implementation of MS4 permit requirements in California, and discuss and demonstrate appropriate methodologies for valuing those benefits.