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CLARK ENGINEERING COMPANY 2815 WAYZATA BLVD. � MINNEAPOLIS, MN. 55405 ; (612) 374-4740 FRANK G PRANKOSK V JA ft"" "tt ►ANDat I M CICI JIMD BRAUCMER Ya* AN1+MN C"ARLESI MANSE% Mich 3, 1978 City of Orono P.O. Box 66 Crystal Bay, MN 55323 RE: THE FARM AT LONG LAKE Gentleman: LARRV G %kVURiRv BRUCE R KILL E A,Wc 44 DAVIDN btENA� A� V-. t EbLit G RENSIC -LER A WKYt\ The proposed plat, "The Farm at Long L0•e", contains a drainage way ►ihic1', will be crossed by the driveway to be conI,tructed on Outlot C. It is proposed to provide a corrugated metal culvert to accommodate this drain- age. Because there is a relatively large area drained into the plat from thz west and north a drainage st6dy was conducted to determine possible peak flows ana adequate culvert sizes. Becau,c: the backup of flood waters to a height somewhdt over the top of the low point in the driveway would not cause damage to buildings nor flood basements, a design storm frequency of 10 years is considered con- servative. The watershed is divided into two parts. The first is that which drains to Brown's Lake west of Brown Road ar:d the second part is that which drains from the north. The two parts have distinctly different runoff patterns because the first has storage in the Lake and the second has direct runoff. In a stony situation runoff from the north will peak long before runoff from the west. The attached drawing shows the pro- posed plat and watershed. The outlet from the Lake is d 24 estimated that a 10 year frequr raise the lake about 3 inche, , cu. ft./•.ec. of flow. The nur'.-,I peaking in about 20 minute% at j I I L_ CONSULTING ENGINEERS STRUCTURAL • CIVIL LAND SURVEYING ::'ir culvert under, P,►otivn Road. It is ,,torw of 60 minute duration will 4pptii would contribute about 1.4 It -a Will Lnnuibute an amount ►-dti ;I altaut IA8.'1 cfs. 400 SI BL E Y ❑ ST PAUL, MN. 55101 (612) 291 7000 u 310 SOUTH LINCOLN STREET ABERDEEN, S U. 57401 (6061 22b-:3494