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bounded by single-family dwellings from l5th Avenue to 3rd Avenue. Commercial and industrial buildings occupy the Spring Gulch floodplain from Third Avenue to the confluence with St. Vrain Creek. Loomiller Basin is totally developed with residential and commercial buildings. . The Town of Lyons is located in north-central Boulder County, approximately 40 miles north of Denver. In 1970, the population of Lyons was 958 (Reference 15), and was estimated at approximately l,300 in 1980. Nearby communities include Longmont, 11 miles southeast; Boulder, 16 miles south; and Estes Park, 20 miles northwest. Lyons is bordered on all sides by unincorporated land of Boulder County. Rainfall in the mountains west of Lyons averages approximately 17 inches annually. The average annual temperature in the basin is approximately 40oF. The basin topography changes from forested mountain terrain on the west, to rolling plains on the east, which are primarily pasture and cultivated fields. The drainage area at Lyons is 219 square miles, with l25 square miles on North St. Vrain Creek and 94 square miles on South St. Vrain Creek. North St. Vrain Creek enters the town on vacant land near the northwestern corner of the community. In the areas south and west of U.S. Highway 36, the existing zoning and land use is primarily residential, consisting of mobile and single-family permanent homes. West of Fifth Avenue the land is vacant. Between Fifth Avenue and Second Avenue, the creek flows through a single-family residential area, north of the business community. South St. Vrain Creek parallels Colorado Highway 7, enters the town near Fifth Avenue, and flows through residential land that is partially developed with single-family residences and mobile homes. St. Vrain Creek roughly parallels the Burlington Northern Railroad east of Second Avenue and flows through open land that is zoned medium-density residential. The Town of Nederland is a small mountain community located approximately 13 miles west of the City of Boulder. The population based on the 1970 census was 492 (Reference l5), and was estimated to be 800 in the late 1970's (Reference 16). Communities adjacent to Nederland are Ward, approximately 7 miles north, and Central City, approximately 12 miles south. North Beaver Creek, draining approximately 5.2 square miles, JOlns Middle Boulder Creek at Nederland. Middle Boulder Creek, wi th a drainage area of 36.2 square miles at the downstream study limit, is a tributary to Barker Reservoir. This reservoir, located approximately 12 miles upstream from the City of Boulder and completed in 1910, has a storage capacity of 11,500 acre-feet and reduces the peak flows of floods originating from Middle Boulder Creek and North Beaver Creek. Rainfall in the basins averages 24 . 12