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• Memorandum • DATE: December 3, 1999 TO: Jeff Smyser FROM: John Powell RE: Highland Mea ws Review of Revi ed Preliminary Plan Grading, Drainage & Erosion Control Plan 1) The storm sewer design does not provide a minimum velocity of 3 feet per second and adequate cover over the pipe per City standards. The storm sewers are designed for a 10 -year event. The system can be designed for a 5- year event. 2) Existing condition runoff computations must be submitted for the 1 year and 10 year events. 3) Equalizer pipes and culverts are to be a minimum of 18 -inch diameter, RCP. 4) This project required Board action by the Rice Creek Watershed District (RCWD). The conditions placed on the site grading and wetland mitigation by the RCWD at their November 24, 1999, meeting must be complied with. 5) The emergency overflow elevations need to be indicated on the plan. The emergency overflow for the central wetland is not clearly indicated. 6) Wetland flood elevations must be shown. 7) The lowest opening elevation of Lot 4, Block 8, must be raised from 907.4 to 908.2. The minimum basement elevations adjacent to ponds 1 and 2 is 907.0. 8) The ability of the downstream ditches to convey the flow must be verified. 9) Easements must be reviewed to ensure coverage of wetland and pond areas. Street and Utility Plans 1) The existing cul -de -sac on Marilyn Drive will be removed during the street construction. 2) This project will add a significant number of trips to the adjoining roadways. Consistent with the previous recommendations for this subdivision, the developer should contribute to the cost incurred to reconstruct 79th Street east of the project and is to place a bituminous overlay on Marilyn Drive between the plat and 77th Street. The previous recommendations also required an overlay on 77th Street from Marilyn Drive to Lake Drive. However, the portion of 77th Street reconstructed as part of the Lake Drive Trunk project can remain as is. The removal and reconstruction of 79th Street was also necessary to provide utility service to the plat. 3) All construction traffic is to be routed out 79th Street to the east. If you have any questions, please let me know.