Examining the Geomorphic Form and Function of the Putah Creek Nature Park Restoration Project

In the fall of 2011, the Putah Creek Nature Park Restoration Project was completed. The project was divided into three phases. Phase I and II were completed in 2011, and Phase III was slated for 2015. The goal of the ecological restoration project was to convert the incised and channelized stream into one that would more closely resemble a single channel alluvial river and that would self-form and periodically inundate its floodplain. After construction of the project, geomorphic surveys were conducted for three years. A meander migration model was used to predict the future form of the as-built channel and the Phase III conceptual channel.;The geomorphic surveys showed that the as-built channel has aggraded in portions of Phase I and Phase II, though not significantly. Some areas of aggradation within the channel were most likely caused by erosion that resulted from construction practices and planting activities within the restoration reach. The surveys also showed that portions of the channel were not constructed with riffles and pools in the general locations that could be found in a self-formed, alluvial channel. Calculations of the existing channel capacity compared with the 1.5 year recurrence flow (743 cfs) shows that the channel was not constructed with dimensions that could convey the 1.5 year flow. Overall, the channel can convey the required maximum flow (46 cfs) under the Putah Creek Accord, and there is floodplain connectivity. Using the 1.5 year recurrence flow as a base of analysis, the channel is undersized and may undergo significant changes in channel geometry if the past flow regime continues.;Based on the assumption that the channel will maintain its current dimensions and that the log and rock revetments will remain in place, the meander migration model predicts that a majority of the channel will migrate both downstream and laterally. The sections that have bank constraints would remain fixed and the channel would be prevented from migrating towards the pedestrian and road bridges, as well as toward Putah Creek Road. The model also indicates that some of these structures were located in areas where there is likely to be little to no migration, even in the absence of constraints.;In conclusion, the project was designed with a planform similar to that of a self-formed, alluvial channel; yet, some sections of the channel have dimensions and bed topography that would not commonly occur in a channel of this planform. The meander migration model predicts that the channel will migrate and be dynamic. The project may have been served better if the channel was constructed with dimensions that could convey the 1.5 year flows throughout the project, and the channel was modeled pre-construction to determine the appropriate location of bank stabilization features, which could have saved time and money. With only three years of data, and with an existing drought during the data collection, more monitoring is needed before a trend can be firmly defined. Also, because the channel is regulated, it would take a number of large storm events, over a long duration to see significant adjustments in the channel.