Pleasants Creek Assessment (Solano County, CA)

An evaluation was made in the summer of 2004 to determine the effectiveness of the various stabilization methods installed on the upper portion of Hoskin's property. It was determined from this assessment that the rock vanes along the outside of meanders performed best in this difficult setting. With severe vertical incision that tends to concentrate flood flows within the channel boundaries, stabilization structures are at risk of flood damage during peak flow events.

This is especially true if such events occur during the first season after project completion, before the riparian vegetation has a chance to offer some resistance to erosion. Such flood flows did occur after the initial work was installed in summer of 2002 and damage was documented to some of the root wad revetment when flows cut behind the structures. While other root wad revetments held in place, it was determined that such revetment in incised channels introduced unacceptable levels of risk. The rock vanes installed in other areas remained intact, with only minor scour damage. In one area the vanes helped to aggrade the channel with new material while protecting the outside bank. It was also noted that areas with developing floodplain surfaces within the confines of the gully walls, tended to be more stable due to reduced bed and bank shear stress.

With this information, the lower sites were designed with use of rock vanes and a floodplain elevation bench to allow for additional flood dissipation. The project was undertaken on the lower portion of Hoskin's property in September of 2004. In addition to the stabilization structures and bench formation, the steep cliff along the outside of three meanders was laid back to a slightly gentler slope to assist in the revegetation of the slope. Native seed and straw was supplied by Hedgerow Farms near Winters. An irrigation system was set up to speed up the germination and growth process along the new floodplain benches. During a spring 2005 inspection, the benches were green with new growth and the rock vanes had successfully protected the bench areas from significant winter and spring runoff.

Photo Gallery - click to open thumbnails
Eroding Cliff face along Pleasants Creek prior to project.	Construction of rock vanes and floodplain bench (September 2004).
Rock vanes protecting new floodplain bench. (April 2005).	Same site as above photo in April 2005.
Vegetative recovery after first runoff season. (April 2005).