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6.0 OTHER STUDIES . . A Flood Plain Information Report was prepared in January of 1969 for Left Hand Creek by the U.S. Army Corps of Engineers, O~aha District (Reference 3). ~he lOa-year flood elevations plotted in the =1000 Plain Information Report do not agree wit~ tnose used in this study. This is due to channel im- prove~ents i~plemented alo~g the study reach in the interim, which confine water to the cha~nel during low frequency events. Previously, large flooes were allowed to spread out over the presently developed flood plain. The improvements generally consist of a 20 ~oot wide channel, 10 feet deep, with 2:1 side slopes which will convey the lOa-year event. The SOQ-year flood will be conveyed in part along Missouri Avenue and in the yards of the adjacent properties. In June of 1972 the Soil Conservation Service completed a Flood Insurance Study enco~passing the unincorporated areas of Boulder County in which Left Hand Creek was studied in detail (Reference 18). Water-surface profiles and flood plains for Left Hand Creek from the Soil Conservation Service study do not agree with this study for the same reasons stated above. A Flood Plain Information Report was completed in June of 1972, also by the U.S. Army Corps of Engineers, Omaha District of- fice, for Lower St. Vrain Creek (Reference 4). The lOa-year water-surface elevations computed for this study are generally within 0.5 foot of those plotted in the St. Vrain Creek Flood Plain Information Report. Two previous hydrologic investigations were conducted for the City of Longmont on Spring Gulch. The first investigation was completed in June 1971 by the U.S. Army Corps of Engineers, Omaha District office. The lOa-year discharge computed for this study at 9th Avenue was 3200 (cfs) (Reference 12). A second study cospleted in 1973 by Bruns, Incorporated (Ref- erence 11), gave a lOa-year discharge of 2117 (cfs) at the Oligarchy Ditch crossing or Spring Gulch. This discharge, however, was based on the asslli~ption that certain detention facilities woald be constructed upstream. These improvements have neither been constructed nor funded. Both the U.S. Army Corps of Engineers and Bruns, Incorporated were contacted to verify assumptions made in their runoff calculations. Based on existing conditions the discharges computed for this study agree with those computed by the G.S. Army Corps of Engineers. Ko published reports or information are available regarding possible flooding on Dry Creek or Loomiller Basin pertaining to flood profiles and flood plain limits referred to in this study. 29