Water Resources Collections and Archives

Between 1960 and 1990, Tassajara Creek in Dublin, CA underwent incision due to anthropogenic sources. The downcutting of the channel bottom was problematic because the process built upon itself and caused disconnection between the channel and floodplain. The incision of Tassajara Creek created a flooding problem and motivated the search for solutions. The need for flood control increased as development increased around the creek. During the 1990s, plans were made to restore Tassajara Creek and provide flood control through the creation of a compound channel. In addition to drainage, the restoration plan’s secondary goals were to increase vegetation, riparian habitat, and public access. A one-mile reach of Tassajara Creek was reconstructed in 1999 and a series of post project appraisals have been conducted since with mixed results. We reviewed and summarized the results of the past studies. We continued the monitoring of the channel evolution by resurveying three of the established cross sections and a partial long profile and compared our data to previous data sets. We also conducted a qualitative analysis of the project’s secondary goals by through observations and photograph comparisons. Our survey data indicated that deposition was occurring on the majority of the floodplain. The channel bottom evolved differently between cross-sections. We found instances of local incision for the most upstream cross-section, E-E’. The channel bottom for the more downstream cross-sections F-F’ and G-G’ aggraded especially at G-G’ where dense cattails encouraged aggradation in the channel. We concluded from a comparison to previous data that the channel is still actively evolving since there was no clear trend towards either incision or aggradation. Our comparison of previous with current photographs showed an increase in vegetation since 2004. The further downstream reach had a lot of diverse vegetation which provided habitat for macroinvertebrates. We concluded the secondary goals were well achieved with a significant increase in the amount of vegetation and habitat with a healthy population of macro-invertebrates.