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Mr. Crellin Scott July 30, 2002 Page 3 of 3 the 100-year. 6-hour amount. The SEDCAD 4 analysis indicates that the routed peak discharge during this event would overtop the embankment by 0.16 feet. Based on the information provided by Colowyo Coal Company, the Gulch A Pond meets the (SCS) TR-60 classification criteria for a Class A Dam. The pond is located in an agricultural area where failure is limited to damaging farm buildings, agricultural land, or county roads. However, the dam classification system considers several other factors that are objective (Earth Dams and Reservoirs. Technical Release No. 60, Page 1-1). For example, consideration is given for existing and future development and the effect of failure on public confidence. Future development in the mountains of Colorado is difficult to predict. Dams are classified as Class B Dams if failure may damage isolated homes, main highways or railroads or internipt service of relatively important public utilities. The proximity of the Gulch A Pond to State Highway 13 could potentially elevate the Gulch A Pond to a Class B Dam but, the Gulch A Pond is located across Good Spring Creek from State Highway 13. Good Spring Creek provides a buffer to State Highway 13 in the event of a Gulch A Pond failure. As a Class A structure, the Gulch A Pond is not necessarily required to meet the TR-60 Emergency Spillway Evaluation and the TR-60 Emergency :ipillway Freeboard Evaluation conditions (items 11 and 12 above). However, the TR-60 Emergency Spillway Freeboard Evaluation indicates that the Gulch A Pond embankment will overtop by 0.16 feet. Therefore, if Colowyo Coal Company wants to meet the CIass B Dam criteria, the Gulch A Pond embankment should be raised a minimum of 0.16 feet. Sincerely. ~\~~:cQ,, ;, Steve Linse, Colorado P.E.3~009 Project Engineer SL:sb Enclosures cc: Dale Brown File: 99-6'l2 W WC Engineering