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1. Maintain or reduce pre-development discharge rates (rate control) 2. Obtain phosphorus loading rates below existing conditions (P-Reduction) ; It should be noted that the City will continue its policy of site plan review to ensure that runoff management features meet the requirements and objectives of this SWMP. MAP DESIGN Ponds, storm sewers, and open channels are shown on the map. The runoff management system is broken into segments by node designations. These nodes identify the addition of flow into the system from drainage areas or pond outFlows. The node-by-node capacity and the size of the existing and proposed storm sewer pipes are presented in Appendix B. Other conveyances and flow control structures are also indentified in Appendix B. APPENDICES Pond data, including type, tributary area, pond area, storage volume, normal and high water levels, and pond outflows are presented in Appendix C. These pond design details are presented for the 100-year event. In addition, pond normal water levels, high water levels, and peak outFlows are presented in Appendix D for the 1-year and 10-year events. Water quality pond data are presented in Appendix E. Pipe sizes, channel sizes, and capacities indicated for each segment of the proposed system are based on assumed grades. While the pipe size and grade can be changed in the final design, the pipe capacity of each segment should not be changed without additional hydraulic analysis. Generally, the purpose of showing potential pipes for drainage was to estimate the extent and cost of conveyance capacity so that Orono could develop equitable area charges. In reality, the rural development prevalent in Orono leads to more reliance on overland conveyance and not pipe. This is a good thing as overland conveyance provides greater opportunity to treat runoff prior to its entering a receiving water. The pipe network shown on Map 1 also described a conveyance system that operates on a regional basis than what actually has occurred. This current plan continues the trend toward less regionalization through goals and policies that specifically tie project proposers to on-site mitigation. It should also be noted that several land locked basins were shown with outlets in the 2002 Plan. In general, these outlets were intended to provide a maintained normal water level. Orono's land locked basin policy, presented in it's goals and policies; and ultimately intended to be a part of a stormwater management ordinance and restricts the use of outlets for land locked basins. Map 1 still shows these potential outlets, however both for continuity with previous analysis and as a representation of a potential emergency overFlow or drawdown outlet designed according to the land locked basin policy and the unique hydrology of each location. The storage volume and outFlow rate of a pond should be preserved for each ponding area to successfully maintain the integrity of the storm drainage system. Pond areas and water levels may change in the final design of the ponding area to best suit the proposed development. Care must be exercised so that outflow rates do not impede the performance of the downstream drainage facilities. r City of Orono Page 52 Surface Water Management Plan �Bonestroo 000139-09034-0