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�Vc�nci:A,sociatc5. Inc. <br /> I�S�ti Pioneer�reek Ltr. <br /> f.C�. 6ox 428 <br /> Maple Plain,MN 55359-0428 <br /> � ����� (612)479-4200 <br /> — � I,ix iF,121 479-4242 <br /> l � � ��._ � � ,i��, <br /> June 30, 1999 � <br /> Mr. Greg Gappa, P.E. <br /> Public Service Director <br /> City of Orono <br /> P.O. Box 66 <br /> Crystal Bay, MN 55323-0066 <br /> Re: Required Drainage Evaluation (Winton Site) � �� � �"�V�� �, ! ���.� �/i����� <br /> Wenck File No. 0905-01 ��1 V <br /> Dear Mr. Gappa: <br /> Wenck Associates,Inc. (Wenck)was retained by James McNeal Architects to determine an appropriate <br /> high water elevation(HWE) in the drainageway adjacent to the proposed building site on the above <br /> referenced site. The site is approximately 2.5 acres in size and is located south of Colin Drive and west <br /> of South Brown Road in Orono. <br /> The site has a direct drainage area of approximately 4.7 acres. The site has a total drainage area of <br /> approximately 23 acres including nearly 16 acres from the City of Long Lake(Long Lake SWMP Dec. <br /> 1998). However, storm water storage and attenuation for all but 2.9 acres of drainage, is significant with <br /> three large wetlands, extensive ditch storage and numerous culvert restrictions. The existing control for <br /> most of the tributary drainage area is a 12-inch CMP culvert under Colin Drive. The proposed drive will <br /> be constructed with a 15-inch CMP culvert and will serve as the new control for the drainage swale <br /> leading to the steep ravine that drains the site to the south. Despite a very wet spring, during a site visit <br /> on June 8, 1999 there was no standing water in the drainage swale downstream of proposed drive. <br /> The HWE for the drainage swale adjacent to the proposed new home is estimated to be 963. The HWE <br /> was estimated by calculating peak inflows to the swale from the proposed 15-inch culvert and the <br /> approximately 2.9 acre drainage area tributary to the swale. Haestad Methods, Inc. open channel flow <br /> module was then used to calculate the flow depth for the channel configuration shown on the site plan. <br /> The calculated flow depth was then rounded up to the nearest foot. (See attached flow calculations) <br /> The 963 HWE is based on the May 24, 1999 site plan and topography provided to Wenck by James <br /> McNeal Architects. Survey data was obtained by Precision Surveys, Inc. Modifications of the drainage <br /> swale, from its existing condition as depicted on the above site plan, may impact the HWE. <br /> Please call me at(612)479-4224 or Kelvin Retterath at(612) 332-4790 if you have any questions <br /> regarding our review. <br /> . <br /> Sincerely, �v 1Q�''i,a e� �^ I - � C� G <br /> WENCK ASSOC , INC. � <br /> l � �--- c�, <br /> �'� <br /> Andrew E. Syverson, .E. <br /> Associate <br /> cc: Kelvin Retterath, James McNeal Architects <br /> \\WENCK-FSl\VO[.1W DRIVE\0905\01\LGG06219.DOC <br />