Telegraph Canyon Creek Basin is an elongated drainage area comprising about 4,800 acres, or 7.5 square miles, in San Diego County. It is located about 8 miles south of the City San Diego. The creek flows through unincorporated County territory and the City of Chula Vista. Because of the serious potential flood hazard to a highly developed area, the County of San Diego and the City of Chula Vista have sought aid to provide improvements along Telegraph Canyon Creek to protect the area. The selected plan would consit of (1) a 0.7 mile-long rectangular concrete-lined channel from a point about 500 feet upstream from 4th Avenue (near 3rd Avenue) to 0.3- miles upstream from Interstate 5; (2) a 0.3-mile-long section comprising double 10x12-foot boxes of covered channel connecting the rectangular channel to the existing 0.2-mile culvert under Interstate 5, which would be incorporated into the project; (3) a 0.3-mile-long concrete trapezoidal channel downstream from Interstate 5; and (4) a 0.1 mile-long earth-bottom trapezoidal channel leading into the San Diego Bay. This plan would provide protection from a 100-year flood. In Reach II there would be some bridge modifications and channel clearing. Construction of Reach I improvements is not dependent upon construction in Reach II. The total cost of the selected plan in Reach I including study costs would be $5,390,000 (April 1983 price levels) with annual charges, not including study costs, off $394,000 and annual benefits equal to $430,000. The benefit-cost radio would be 1.1.