Water Resources Collections and Archives

Stormwater can contaminate water supplies and cause biological impacts to streams, estuaries, and coastal zones due to excess sediment, nutrients, pesticides, or heavy metals. Best management practices (BMPs) for stormwater control are implemented with greater frequency now that municipalities are required to have a National Pollutant Discharge Elimination System (NPDES) permit according to Clean Water Act revisions. After BMP construction, however, engineers and hydrologists rarely conduct follow-up assessments or evaluations. For this project, we evaluated the effectiveness of the Tule Ponds in Fremont, a constructed permanent wetland designed to simultaneously treat urban runoff and provide wildlife habitat. Using survey measurements of the pond dimensions and elevations, wildlife observations, and conversations with the site manager, we analyzed the success of the original wetland design. While our findings indicate the ponds did not function exactly as intended, they still succeeded in reaching overall intended objectives. The ponds catch, retain, and treat stormwater; however, the banks were unstable and have eroded, and the system dries out almost every summer due to infiltration into the ground. Based on current BMP guidelines, the ponds are too deep in winter, their banks are too steep, and emergent vegetation is insufficient. These factors may limit the ability of the wetland to support aquatic wildlife, and may limit contaminant removal. In addition, excess pond depth and algal growth result in low oxygen levels. Still, the site is populated with common birds (Canada geese, mallards and egrets), amphibians (bullfrogs and Pacific treefrogs), and insects (dragonflies and damselflies). We examine trade-offs between multiple use aims of this wetland system. In addition, because the site is only accessible through scheduled classroom field trips and is not generally open to the public, Tule Ponds may represent a missed opportunity for broader public education about urban ecology and stormwater management.