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STORM CHARACTERISTICS AND RAINFALL INFORMATION The summer storm that produced flooding in the Buffalo Creek area was a typical convective type cloudburst event. These events are not uncommon along the foothills and plains east of the Continental Divide in Colorado. Storms like this form quickly and can produce large amounts of rainfall, hail, and severe weather conditions within a short amount of time. At this time, only preliminary information is available describing the particular storm over Buffalo Creek. The preliminary information is based on field analyses, rain gage information, and interviews with witnesses and local residents. The preliminary information indicates that the storm moved from west to east and then stalled right over the lower part of the Buffalo Creek watershed. The most intense rainfall amounts, which fell over Buffalo Creek, are estimated to be from 2 inches to 3.5 inches within 30 to 90 minutes. The storm may have covered an area between 10 and 30 square miles. There is some uncertainty about the antecedent moisture conditions prior to the storm event. Some evidence suggests that there may have been up to a half inch or inch of rain within a few hours prior to the thunderstorm event, however there are conflicting reports from local residents. It is not necessarily uncommon for Buffalo Creek to receive rainfall totaling 2 inches. However, the intensity or rate of the rain for this storm (heavy rain over a very short duration) may be a much less frequent event. To provide a point of reference, the average annual rainfall for the foothills of southern Jefferson County is about 10 to 12 inches, and the lOO-vear, 6-hour rainfall depth is reported to be about 2.5 inches according to the NOAA Atlas 2 for Colorado (National Weather Service, 1973). To provide a more detailed reconstruction of the storm event, all possible information is currently being collected from the National Weather Service, private meteorologists, and other entities. Local residents will be interviewed, and "bucket surveys" will be documented as well as possible. This information will help describe the storm's track, aereal extent (where the precipitation fell), rainfall and hail amounts, intensities, and other conditions. The collection and analysis of detailed precipitation information is one of the most important elements in researching and reconstructing this event. HYDROLOGY AND HYDRAULICS Peak discharges for the July 12 event for the North Fork, Buffalo Creek, Sand Draw, and other tributaries were estimated by the USGS and the Colorado Water Conservation Board. The CWCB obtained detailed surveyed cross-sections at one location on the North Fork, one location on Sand Draw, and four locations on Buffalo Creek. The cross-section locations were carefully chosen to avoid places that had unusually high amounts of sediment deposition and places that may have had backwater or ponding effects from bridges or other features. High water marks and channel slopes were surveyed. Discharge estimates were made using Manning's equation with the collected field data. Since Manning's equation considers only clear water discharge, Manning's "n" values were adjusted upward to take into account the debris and sediment that were present in the stream flows c;