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i <br /> ORONO COUNCIL AZEETING HELD SEPTEl�BER 27, 19'15 Page 22 <br /> , EXISTING DRAINAGE VOLU��iES e The drainage area FARVIE6�1 STORM WATER PLAi�1 <br /> described above consists of approximately 1'7, 3 <br /> �cres. Based on a current runoff coe�`ficient o�' �Continued) <br /> 20�, and a 100-year storm with a 20 min�i�� <br /> duration and a rainfall intensity of 6-inches/hdu�, <br /> � the discharge from the watershed is 2b. E3 cuk��.c <br /> feet per second, <br /> � <br /> . FUTURE DRAINAGE VOLUP�ESs The developer pro�t�ses <br /> the introduction of roughly 1.0 acre� o� impervious <br /> � covers, calculated as followso <br /> � 6 Houses @ 2500 SF = 15,000 �F <br /> 6 Garages @ 600 SF = 3,6�� ��' <br /> � 6 Driveways C 100 ° <br /> • X 15 ' = 9,Ot�C� 9�' <br /> Streets @ 24' X 650 ° = 15,�i�� 5t <br /> S TOTAL 4���C�0 S�` <br /> • IIased on a runoff coeffiai�nt d� 50�a for these <br /> � impervious areas and 20� �o� �he �`emaining 16. 3 <br /> acres, the 100-year storm wi 1 re�ult in a runoff <br /> � volurie of 25.0 cfs, repre�en�irit} � 20� increase <br /> frcm the current volum��o <br /> • DRAINAGE PROPOSAL: To ha�1c�1� the �.i�creased drainage <br /> �olume, the developer pi^opos�s to construct a <br /> rainage ditch in the easeme}it area adjacent to <br /> * the south property �iii� of tfie development, <br /> The ditch will s���t dt rqugh�.y the west property <br /> � line of Lot 10 and thr�n flbw easterly to a <br /> storage pond in the southeast corner of Lot 12. <br /> The pond will have a minimum storage volume of <br /> 5,000 cubic feet to handle the increased runoff <br /> • volumes from the 100-year storm, calculated <br /> as follows e (25 e 0 cfs - 20 0 8 cfs) X 20 r.iinutes X <br /> � 60 seconds/minute - 5000 Co Fo The ponr? would <br /> be roughly 100' X 100 ° X 6" deep on ponding area, <br /> � We recommend approval of the drainage plan <br /> subject to the followinge <br /> • <br /> • 1. The developer should provide an easement for <br /> the ponding area, <br /> � 2. Culverts will not irnpede or interfere with <br /> approved drainage velocity and volumes, <br /> � 3. Elevation of control structure at northwest <br /> area shall be approved by the Engineer and <br /> � shown on the final plato <br /> 4. The drainage ditch flowing east should be <br /> constructed by the developer within the boundaries <br /> of the easement being provided, <br /> 5, A drainage ditch flowing west from approximately <br /> � the west property line of Lot 10 should be <br /> constructed within the boundaries of the <br /> easement being provided. (Continued) <br />