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<br /> <br />Flood and the Standard Project Flood are des- <br />cribed and discussed. <br /> <br />INTERMEDIATE REGIONAL FLOOD <br /> <br />The Intermediate Regional Flood is a flood <br />having a one percent proba'bility of occurrence in <br />any year or an average frequency of occurrence in <br />the order of once in 100 years. The flood may OCCur <br />in any year. The probable magnitude of this paten. <br />tial flood was developed from a study of stream <br />gaging records. The Intermediate Regional Flood <br />discharge for Boulder Creek at Boulder is 7,400 <br />c.f.s. For a measure of comparison - the flood <br />of 7 May 1969 was estimated to be between 2.500 <br />and 3,000 c.f.s. near Broadway. <br /> <br />STANDARD PROJECT FLOOD <br /> <br />The Standard Project Flood is the flood that <br />may be expected from the most severe combina. <br />tion of meteorological and hydrological conditions <br />that are considered reasonably characteristic of <br />the geographical area in which the drainage basin <br />is located, excluding extremely rare combinations. <br />The Standard Project Flood discharge for Boulder <br />Creek at Boulder is 15,800 c,f.s. <br /> <br />POSSIBLE LARGER FLOODS <br /> <br />Floods even larger than the Standard Project <br />Flood are possible. but the combination of factors <br />to produce such floods would be extremely rare. <br />Such floods are not further discussed in this reo <br />port, although they should not be overlooked where <br />absolute safety from flooding is a requirement. <br /> <br />AREAS FLOODED AND DEPTHS OF <br />FLOODING <br /> <br />Those areas of Boulder in the study reach that <br />would be flooded by the Intermediate Regional or <br />Standard Project Floods are shown on the map on <br />the reverse side of this fold.out sheet. Topographic <br />maps with 2 foot contours were used as a base for <br />plotting the flood outlines from profile data. The <br />maps were produced by photogrammetric methods <br />using aerial photographs flown in December 1970. <br />The outlines were transferred to the photo mosaic <br />for presentation in this report. Actual flood limits <br />on the ground may vary from those shown due to <br />map limitations. Flood profiles show stream fea. <br />tures and bridges relative to the water surface of <br />the two large potential floods. Typical flood depths <br />are shown on the cross sectional views. More pre- <br />