Paul Detjens is driving us from his Martinez office to a restoration site near the mouth of Walnut Creek on Suisun Bay, a project he spearheads as an engineer for the Contra Costa County Flood Control District. These lower reaches of the creek — straightened, widened, and leveed by the U.S. Army Corps of Engineers — have been a sluggish, silt-filled problem for more than half a century. Detjens has worked to find a solution for the last 17 years.