An Analysis of the Effectiveness of Various Management Strategies of Small Urban Reservoirs for Improving Water Quality

Abstract:

Small urban reservoirs, some more than 100 years old, are scattered throughout the San Francisco Bay (SFB) area. Because of the small size of these reservoirs, many of them are locally managed and provide an opportunity to investigate various management strategies on in-lake and downstream water quality. We studied three small, urban reservoir-watershed systems in the SFB subjected to differing water quality impairments to determine which management strategies might be most effective for improving water quality.

The three study reservoir-watershed systems were monitored biweekly for water quality at the reservoir inlets and outlets and in the lakes through surface to bottom depth profiles. Measurements included pH, conductivity, dissolved oxygen, temperature, nutrients, and metal concentrations. In addition, sediment cores were collected and analyzed for metal and nutrient concentrations, with chronologies assigned based on Pb-210 and Cs-137 data.

One watershed-reservoir system is managed with the reservoir cyclically empty (during winter months) and full (during summer months), whereas the other two watershed-reservoir systems are managed with the reservoir always full, albeit to varying levels. Results indicate the ideal management strategy depends upon the primary pollutant of interest and may not be the same in all urban reservoir-watershed systems. However, overall water quality may generally be improved with continuously full reservoirs with occasional, controlled drawdown. Continuing experiments are investigating the role of microbes in pollutant cycling in these reservoirs it their relation to reservoir full versus reservoir cyclically empty management strategies.