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Large temperature changes are observed at Stapleton International Airport during the year, where the monthly average varies from 29.7 degrees Fahrenheit (OF) in January to 72.90F in July. The mean maximum varies from 43.40F in January to 87.40P in July, while the mean minimum varies from 16.0oP in January to 58.30F in July, 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 observed..-- downtown over a 23-year duration. Both stations show a distinct maximum in spring and summer, with a minimum in the winter season. Spring and summer bring much more frequent movement of air from the south and more solar radiation to produce convective showers. Average annual snowfall measurements are 66 inches at the 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 speeds vary from 8.2 miles per hour (mph)in late summer and early fall to 10.4 mph in April (Reference 1). The soils in the Denver area are generally deep, well-drained, clayey soils that are neutral or mildly alkaline (Reference 2). There are significant sand and gravel deposits along the major streams in the city. These include deposits along the South Platte 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 the South Platte River. It flows 380 miles from its headwaters at the Continental Divide in Park County to its confluence with the North Platte River at North Platte, Nebraska, where the drainage area is approximately 24,300 square miles. The drainage area of the South Platte River in Denver is approximately 3,800 square miles. The major tributaries to the South Platte River in the Denver area are Cherry Creek (drainage area 410 square miles), Sand Creek (drainage area 189 square miles at Quebec Street), Clear Creek (drainage area 575 square miles), and Bear Creek (drainage area 261 square miles at the mouth). 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 a smaller basin where a large amount of residential development is occurring. Clear Creek, Sand Creek, First Creek, and First Creek Tributary are larger basins with most of their development at the lower end of the basins near the confluence with the South Platte River. The Bear Creek floodplain has moderate residential development, with some open space and industrial commercial areas. The other major drainageways are fully urbanized in the Denver area and are bounded by residential development with the exception of the South Platte River and Cherry Creek, which also flow through commercial and industrial areas. 7