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. _ , : ~ III 1111111111111111 ~, <br />Leonard Rice Consulting Water Engineers, Inc. <br />(303) 455-9589 / 2695 Alcott Street / Denver, Colorado 80211 <br />October 21, 1980 <br />Leonard Rice <br />Leslie H. Bothem <br />Gordon W. Feesett <br />Mr. Dan Corson <br />Norton Frickey b Associates <br />151 Federal Blvd. <br />Denver, CO 80219 <br />RE: Reported Weld County Gravel Mining Operation, St. Vrain <br />Creek <br />Dear Dan: <br />At your request, we have investigated the adequacy of the <br />flood plain planning that is associated with an existing <br />gravel mining operation in the flood plain of St. Vrain <br />Creek in Weld County. It is reported that Weld County is <br />the operator. Our investigation has been limited to analysis <br />of air photographs dated October 27, 1979 and June 9, 1980 <br />and on a field inspection conducted September 13, 1980. The <br />site in question is located in the southwest quarter of the <br />southeast quarter of Section 35 of Township 3 North, Range <br />68 West, 1/2 mile east of I-25. <br />In connection with Weld County's reported gravel mining oper- <br />ation, the natural ground between the lakes and the creek has <br />been removed. This has gre~atl~ increased the chance that the <br />river may, during times of hig~i flow, relocate through the <br />gravel operation. Mr. Slovak's property is located immediately <br />downstream and on the same side of the river, If the river <br />were to relocate further south, his property could be seriously <br />damaged. A graphic demonstration of the potential for damage <br />occurred on May 1, 1980. On that date, an estimated 300 to 500 <br />cfs flowed from the creek through a breach in the dike separating <br />the gravel operation's eastern lake from the creek, over the dike <br />at Mr. Slovak's western line and on to his property. At the <br />time of she flood, the natural channel bank was intact except <br />for the 20 foot breach. The U.S. Geological Survey estimated <br />that the peak flow of St. Vrain Creek at Longmont (about 7 miles <br />upstream) on May 1, was only 2380 cfs. Under present conditions, <br />a flood of even this low magnitude might relocate through the <br />gravel operation and threaten Mr. Slovak's property. <br />We have helped many gravel mining clients prepare applications <br />4` \ f1f' <br />HydrolOQy ~ <br />Water RIph4 ~ : ~ <br />Envlronmentel Anelyele ~ „~ <br />Urbsn Drefnepe `•~~°` <br />