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<br />.' <br /> <br />, <br /> <br /># Mr. Douglas Differt <br />December 21, 1981 <br />Page 2 <br /> <br />~ <br /> <br />'') <br /> <br />The following chart summarizes the effect of the water retention <br />area on peak flow at the I-694 culverts (calculations by Barr <br />Engineering): <br /> <br />Condition <br /> <br />Water Flow @ <br />100 Year Event <br /> <br />Water Flow @ <br />50 Year Event <br /> <br />Primitive: <br /> <br />39 <br /> <br />30 <br /> <br />Developed: <br />(uncontrolled) <br /> <br />58 <br /> <br />48 <br /> <br />Proposed <br />Developed: <br />(4 acre-feet <br />water storage) <br /> <br />30 <br /> <br />26 <br /> <br />.i <br /> <br />The proposed retention area requires extensive grading to produce <br />the necessary retention height. The constraints of the site <br />necessitate some changes in grade on the I-694 right-of-way. <br />All changes have been designed to have minimal impact on the <br />highway: the ditch within 30' of the road would not be disturbed. <br />All contours on the upslope from the highway would be maintained <br />at a 6:1 shallow slope. <br /> <br />') <br /> <br />The proposed vegetation at the summit of the dike near the <br />highway fence would be low maintenance shrubs and trees and <br />would not require mowing. Any disturbed area on the slope <br />toward the highway would be reseeded, and erosion contrel <br />through the use of hay bales would be utilized during construction. <br /> <br />The proposed changes on the right-of-way would result in a <br />smoother contoured sloped within 70' of the road surface. <br />The dike summit vegetation, to be maintained by the City of <br />New Brighton, would be a positive visual feature along the <br />highway. <br /> <br />The proposal does not increase the number of storm sewers on <br />the right-of-way: the existing storm sewer that now empties <br />into the ditch to the west of the culverts would be abandoned. <br />All stormwater would be routed through the new retention area. <br />The outlet structure from the retention area has not been <br />fully designed but is envisioned as a skimming weir that empties <br />into a 30 CFS capacity pipe at elevation 865'-0". This outlet <br />would be fully maintained by the City of New Brighton. The <br />existing flow from the culverts under Fifth Avenue would be <br />routed through a separate pipe directly to the culverts under <br />I-694. <br /> <br />~ <br /> <br />,~ <br /> <br />The proposed site development was designed by ArChitectural <br />Alliance and further technical information can be obtained from <br />David Soloman. Hydrologic calculations were performed by <br />