College Lake Improvement and Watershed Management Project

The focus of this project was to develop a multi-objective management plan for College Lake that enhances opportunities for flood reduction, agricultural water supply, and native species habitat in addition to several other objectives. College Lake is a naturally occurring ephemeral water body located along Salsipuedes Creek, a tributary to the Pajaro River in Santa Cruz County, California.

In the current condition, the lake is managed so that it is inundated during the rainy season, and then is pumped dry in the early spring so that farming can occur on the lake bed. A number of agencies have expressed interest in managing College Lake differently. Army Corps of Engineers has proposed modifications to College Lake infrastructure in their plan to reduce flood risks within the Pajaro River system. Pajaro Valley Water Management Agency has proposed modifications to College Lake to utilize the impounded water as a blending source for their agricultural distribution system during the dry season. Other entities have suggested that modifications to the lake’s infrastructure and management could significantly improve the amount and seasonal availability of various habitat types provided by the lake and its associated riparian areas. Until this project, all of these parallel efforts that focus on the same water body had not been integrated.

cbec developed a preliminary multi-objective management plan for College Lake. Components of the analysis included the development of a water budget for College Lake, evaluation of the various proposed alternatives, as well as development of new alternatives which integrate multiple objectives. The water budget is based upon historical data records, field measurements, and a combination of hydrologic and hydrodynamic modeling. Once developed, the water budget and numerical models were used to evaluate: 1) the current condition, 2) alternatives which have been proposed previously, and 3) new multi-objective alternatives development by cbec with input from various stakeholders. Each alternative was assessed with regards to the ability to achieve its specific objectives (e.g., flood attenuation) as well as other possible objectives (e.g., water supply, habitat, seasonal agriculture). The results of the alternatives analysis indicate that flood attenuation, water supply and habitat for native species can all be achieved in a single integrated multi-objective project at College Lake. Subsequent efforts, which are currently underway, funded by Pajaro Valley Water Management Agency, continue flow monitoring to provide data for further calibration and validation of the hydrologic and hydrodynamic models.