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I <br /> EXHIBIT D <br /> ARBORLEAF ENGINEERING <br /> & SURVEYING, INC. <br /> TBPLS#100543-00 TBPE#7705 <br /> 1002 Village Square Drive, Suite B <br /> Tomball,Texas 77375 <br /> 281-655-0634 <br /> I <br /> April 1,2015 <br /> Mr.Bob Eng,P.E. <br /> City Engineer <br /> City of La Porte <br /> 604 W.Fairmont Parkway <br /> LaPorte,Texas 77571 <br /> i <br /> Re: Detention Summary <br /> La Porte Junior High School <br /> ALES Project#15-508 <br /> Mr.Eng, <br /> 1 <br /> This letter provides assumptions and calculations used for the determination of additional detention volume <br /> needed at the site of the new La Porte Junior High School improvements. <br /> Site Information: <br /> i <br /> The property slopes gently to the east with elevations ranging from slightly over 18.0 at the northwesterly <br /> end to roughly 14.0 at the southeasternmost corner. <br /> Existing ground cover consists of school buildings,concrete parking lots,grass,and small trees. The <br /> existing site mostly drains to existing storm inlets located at the parking lots and draining towards an <br /> existing storm sewer located in Arizona Street. The proposed site will continue to drain towards Arizona <br /> Street,while utilizing additional detention. <br /> The property is shown on FEMA map panel 48201 C0945M,and is designated Zone X,which is located in <br /> the 500 year flood plain. <br /> i <br /> The City of La Porte has jurisdiction as the Flood Plain Administrator. <br /> The pond will be designed as follows: j <br /> I <br /> i <br /> Side slopes will be a maximum of 3:1 <br /> The ponds will be fenced <br /> The constructed ponds will be hydroseeded to prohibit erosion <br /> A concrete pilot channel will be constructed in the ultimate pond to facilitate flow through the pond. <br /> The sizing of the ultimate pond volume and appropriate calculations are shown below. <br /> I <br /> I <br />