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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />overtoppi ng and functi on as an auxi 1 i ary spi 11 way. A moderate amount of <br />driftwood is trapped in the ri prap along the upstream face at the hi gh water <br />mark every year but the City has made an effort to remove debris from the face <br />each year. <br /> <br />2.2.4 Downstream Face <br /> <br />The downstream slope of the dam is generally 1. 75H to 1 V above the berm at <br />about el evati on 9382 (G. H. 27.0). The berm is ei ght to ten feet wi de and <br />somewhat undulating in elevation. It was added for stability during the 1966 <br />modifications. The downstream slope of the berm flattens to 4H to lV near the <br />Hourgl ass outl et works and steepens to about 2H to 1 V near the Mai n outl et <br />works. The downstream face has been protected by grass but is cri ss-crossed <br />by foot trails that have not grown back and are susceptible to erosion. <br /> <br />2.2.5 Seepage <br /> <br />The primary concern at Comanche Dam that has led to the present restriction is <br />seepage. Seepage measurement weirs have been in place for years and the City <br />inspects the dam, reads pi ezo~ters, and observes seepage on a daily basi s <br />during the summer ~onths. Although the total seepage volu~ is considerable, <br />the loss is not critical to the economical operation of the reservoir. <br /> <br />Seepage, however, is a serious concern from the standpoint of dam safety. At <br />various times in the past, inspectors have reported boil s of very fine gray <br />sand at several locations in the streambed downstream of the Main outlet <br />works. Sand boils were not observed during any of the inspections, probably <br />due to the restricted reservoir level. However, MKE personnel had observed <br />the phenomena during a visit to the site in 1982 and viewed the photographs in <br />the dam safety reports filed by the State Engineer. The gray sand boil s that <br />have occurred over the years emerge at a different location each time and seem <br />to transport a small quantity of material not present on the surface. <br />Furthermore, evidence of this same fine gray sand along the left side of the <br /> <br />2084H <br /> <br />-4- <br />