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<br />... <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Drainage from Sandpiper Estates is included in the design of the trunk storm sewer. However, <br />the proposed storm sewer collection system for Sandpiper Estates was recently deleted from <br />the Western Area Phase II contract. Continuing to include the area in the design of the trunk <br />storm sewer will enable Sandpiper Estates to be connected into the system in the future. <br /> <br />Also included in the design of the trunk storm sewer is the discharge from the Country <br />Crossings Second Addition proposed pond. This pond will receive stormwater from areas 2, <br />9, and 10 shown on the exhibit. Preliminary design of Country Crossings Second and Third <br />Additions is complete at this time. <br /> <br />TRUNK STORM SEWER DISCHARGES <br /> <br />The peak discharge at the outlet of the 88" span arch pipe to Lake Orono is 136 cfs for a 100- <br />year, 24-hour storm event. The downstream segment of the 88" span arch pipe, from the <br />Police garage driveway to Lake Orono, has a slope of :1:0.09% with a capacity, under gravity <br />full flow conditions, of :1: 108 cfs. Surcharging of the trunk storm sewer will occur along this <br />segment for a lOO-year event. <br /> <br />The upstream ponds at Country Crossing First and Second Additions, along with the future <br />ponds in the areas north of Orono Parkway, have all been checked for acceptable high water <br />levels based on the hydraulic grade line capacity of the trunk storm sewer. Although the trunk <br />storm sewer is surcharged at the outlet, each pond functions correctly, providing adequate <br />freeboard below the proposed homes surrounding each pond. <br /> <br />CONCLUSION <br /> <br />The above information provides proper guidance for continued development of the areas <br />tributary to the Orono Parkway trunk storm sewer. Preliminary design of the areas south of <br />Orono Parkway is already complete. However, planning has not yet started, or has recently <br />started on the areas north of Orono Parkway. As the areas north of Orono Parkway develop, <br />the allowable peak discharges listed in Table 2 provide the framework to begin storm drainage <br />planning for each of those areas. <br /> <br />We appreciate your patience during these past few weeks. Please do not hesitate to call if you <br />have any questions about the information we have provided. <br /> <br />Sincerely, <br /> <br />MSA, CONSULTING ENGINEERS <br /> <br />- <br /> <br />cf)tM( ~,l1rl <br /> <br />~~~ <br /> <br />Terry J. Maurer, P.E. <br />City Engineer <br /> <br />David E. Nyberg <br />Staff Engineer <br /> <br />DEN:tw <br />Enclosure <br /> <br />cc: Mr. Jon Bogart, John Oliver & Associates <br /> <br />223-1303.sep <br /> <br />Page 3 <br />