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Rm. 116, 57 Fairgrounds Dr., Madison, WI 53713 <br /> 1 Phone: 264-5458 <br /> ptember 9, 1980 <br /> Edmond P. Minihan, Chairman <br /> Town of Dunn <br /> Office of Town Clerk <br /> 4156 C.T.H. B <br /> McFarland, WI 53558 <br /> Dear Mr. Minihan: <br /> As requested, we have prepared the following assessment of the runoff problems <br /> located in section 23 near Colladay Point. <br /> There are 189 acres draining to Lake Kegonsa through the problem area. Using <br /> our runoff estimation methods, we come up with fhe following data. Under existir <br /> conditions, a 10-year frequency storm will yield 160 cubic feet per second (cfs) <br /> of runoff volume. A 25-year storm will yield 200 cfs. <br /> To safely carry these volumes of runoff, the following sized vegetative channels <br /> would be needed. (Using one percent grade and 4:1 side slopes) <br /> 160 cfs 200 cfs <br /> Depth 2.4 ft. 2.6 ft. <br /> Bottom Width 4.0 ft. 4.0 ft. <br /> Top Width 23.2 ft. 24.8 ft. <br /> By having needed conservation practices applied in the watershed, the runoff woul <br /> be reduced to 110 cfs for a 10-year storm and 150 cfs for a 25-year storm. <br /> Channels for these volumes with 4:1 side slopes are as follows: <br /> 110 cfs 150 cfs <br /> Depth 21j ft. 2.4 ft. <br /> Bottom Width 4.0 ft. 4.0 ft. <br /> Top Width 20.8 ft. 23.2 ft. <br /> Two to one side slopes could be used. However, that would increase the depth and <br /> because of the lake level, there is not much available. Also 2:1 side slopes pre <br /> greater maintenance problems. <br />