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r <br /> .� <br /> - . i _ <br /> . : . `_, + �. , . <br /> � _ <br /> i '. <br /> . L ' . � .� � r � . <br /> PUBL/C WORK'S �I'�`� <br /> E �rr � � <br /> _ �h ` <br /> REVIEW MEMORANDUM '�` =�i � <br /> � :( "� , � <br /> ��i � <br /> TO: Kirk Brooks ti" i� , <br /> ,� ; <br /> FROM: ]ane Zimmerman � � . ' <br /> \ . ;� <br /> DATE: June 8, 1998 (1�f'y ` � <br /> � �� . <br /> SUBJECT: Drainage Calculations/Requirements,Evergreen Center J ' . `, " <br /> �t' ' <br /> /' �The drainage calculations and storm drainage detention/treatment system require � <br /> modification in order to meet City standards. <br /> (1) The precipitation used in the time of concentration calculation should be the two year�� �l! <br /> precipitation for all storms. The time of concentration is a site condidon (slope, ,,��('�5 , yJ'� <br /> vegetative cover, etc.) vaziable, not a storm vaziable. That is, the time of concentration � eG <br /> for sheet flow conditions, for all storms, is the following: ��� <br /> 9 �n�` ��� <br /> T�=0.4�2 {�nSL�°'8 note: PZ is used in this e uation for all storms � <br /> P` . �So�o.a � � <br /> (2) The upper pond has been eliminated and there are no longer two sepazate "collector" J�l�� ����� <br /> points. Therefore, the site should be analyzed as one basin. �p('� � n� <br /> 1'� Cy <br /> THE DESIGN ENGLVEER SHOULD COMBINE AREA 1 A1YD AREA 2 AND ��`�l �a, p���h <br /> PROCEED AS FOLLOWS: �n �.��} 1 <br /> n <br /> For analvsis of existine conditions and determination of allowable release rates for �� <br /> detention• ��/ ' <br /> 1) Determine one A;mary;o„S and one Aarv;o,� for the exishng site area, so that � I <br /> � � 1g� <br /> Aimp. + Aperv.= Awtal (1.49 acres) �1 <br /> • 2) Determine the time of concentration for the exisdng site conditions. <br /> i 3) Determine Q,y�, Qioy„ and Q�oq,�for the existing site. <br />