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Technical data for flooding on City Park Channel, Nissen Reservoir Channel, and overflow from Brandywine Creek were taken from a report by the Colorado UD&FCD (Reference 1) and the Broomfield Colorado Flood Insurance Study (Reference 2). The areas studied by detailed methods were selected with priority given to all known flood hazard areas and areas of projected development or proposed construction through 1989. Ketner Creek (Reference 3), Shaw Heights Tributary and Little Dry Creek (Reference 4), which were studied previously by the Colorado Urban Drainage and Flood Control District, were included as approximate study areas. Approximate analyses were used to study those areas having a low development potential or minimal flood hazards. The scope and methods of study were proposed to, and agreed upon by, FEMA and the City of Westminster, Colorado. 2.2 Community Description Westminster is located on the east slope of the Rocky Mountains, about 8 miles northwest of the State Capitol Building in Denver. In 1980, the population of Westminster was 50,211 (Reference 5). Continued growth is expected for the city. Big Dry Creek has its source in the Rocky Flats area southwest of the City of Boulder, Colorado,. and is a tributary to Standley Lake. Walnut Creek begins near the Rocky Flats Plant of the Atomic Energy Commission, and is a tributary to the Great Western Reservoir. Little Dry Creek originates just southwest of Standley Lake, passing through Arvada and Westminster to Clear Creek. Airport Creek has its source in the Jeffco Airport area. All of the other streams studied have their sources basically within the city limits, and have little or no flow most of the time. The total drainage area of Big Dry Creek to Interstate 25 is 56.84 square miles, of which 16.75 square miles are above the two reservoirs. Watershed elevations range from approximately 6,500 feet at the headwaters of the drainage area of Standley Lake to 5,160 feet at Interstate 25. The climate of the area has characteristic features of low relative humidity, low rainfall, moderate to high wind movement, and a large daily range in temperature. The annual average maximum and minimum temperatures are 60.2 and 39.1 degrees F. Recorded temperature extremes are a high of 102 degrees F. to a low of -26 degrees F. The average annual precipitation is 15.14 inches. Sixty nine percent of this precipitation falls during April through September. Summer precipitation is largely from thunderstorm activity and is sometimes extremely heavy. Land use within the study area is mixed between commercial and residential, with several parks and open undeveloped areas. 4