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accompanied by a large percenl:ageof sunshine and sizable temperature changes from day to night. Large temperature changes are observed: at Stapleton International Airport during the year, where the monthly average varies from 29.70F in January to 72.9oF in July. T~e mean maximum varies from 43.4oF in January to 87.4oF in July, whale the mean minimum varies from 16.00F in January' to 58.3oF in J~ly, which is indicative of the extent of temperature change from day to night. Average annual precipitation of 15.2 inches at Stapleton International Airport was determined from data taken over a 25-year period, while 12.4 inches was observe:d downtown over a 23-year duration. Both stations show a disqnct maximum in spring and SUllDller, with a minimum in the winter ;season. Spring and summer bring much more frequent movement of a:ir from the south and' more solar radiation to produce convective! showers. Average annual snowfall measurements are 66 inches at ~he airport and 56 inches in the central part of the city. Average winds do not change much throughout the year. The prevailing direction is from the south in every month, and s\l'eeds vary from 8.2 miles per hour (mph) in l~te summer and early fa.~l to 10.4 mph in April (Reference 1). j I The soils in the Denver area' are ge~erally deep, well-dralined, clayey soils that are neutral' or mil~ly alkaline (Referenc1e 2). There are significant sand and gravet deposits along the ,major streams in the city. These include deposits along the South ~latte River, Bear Creek, and Clear Creek. The basins of Sand Creek and Cherry Creek contain fine sand, but little gravel (Reference 1). The major stream in the Denver area is Ithe South Platte River. It flows 380 miles from its headwaters at the Continental Divide in Park County to its confluence with the jNorth Platte River at 'North Platte, Nebraska, where the drainage area is approximately 24,300 square miles. The drainage area of i the South Platte River in Denver is approximately 3,800 square milies. The major tributaries to the South Pla~te River in the Denver area are Cherry Creek (drainage area 410 i square miles), Sand Creek (drainage area 189 square miles at ~uebec Street), Clear Creek (drainage area 575 square miles), and Bfar Creek (drainage area 261 square miles at the mouth). I In most cases, present-day conditions have reached or are approaching full urbanization for major drainage basins in the Denver area. The exceptions include Coon Creek, First Creek, and First Creek Tributary. Coon Creek is ai smaller basin where a large amount of residential development is o~curring. Clear Creek, Sand Creek, First Creek, and First Creek tributary are larger basins with most of their development at the ~ower end of the basins near the confluence with the South Platt~ River. The Bear Creek floodplain has moderate residential ~evelopment, with some open . . 8