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253 the filling of wetlands, resulted in an under-sized storm sewer system for today's 254 conditions. 255 The following areas of concern were identified in the analysis: 256 • The intersection of Draper Avenue and Midland Hills Road 257 The wetland located between 2235 and 2211 Rosewood Lane North ("Rosewood 258 Pond"). 259 • The side yard at 2241 Rosewood Lane South 260 261 This pipe configuration at Draper Avenue and Midland Hills Road creates a bottleneck 262 an the system, which causes localized street flooding in 100, 10, and 5-year events. 263 Rosewood Pond and the side yard at 2241 Rosewood Lane South were identified as flood 264 prone in the 100- and 10- year events. The following table shows the results of the 265 modeling for the flood prone areas. 2241 Rosewood Rosewood Pond Low building elevation 937.60 940.30 100-Year High Water Elevation 939.57 941.42 10- Year High Water Elevation :937..48 940.35 Approximate additional storage needed to accommodate 100-Year event :0.75 ac-ft 1.1 ac-ft 266 The streets in this neighborhood are in good condition; capsizing the entire storm sewer 267 system would not be acost-effective manner in which to improve the drainage 268 conditions, as it would require significant pavement removal and excavation. In addition 269 to costs, capsizing the pipe would increase flow rates into Walsh Lake. Since the outlet of 270 Walsh Lake is controlled by a lift station, increased flow to Walsh Lake could cause 271 significant problems downstream. 272 Creating additional storage possibilities throughout the existing storm sewer system, such 273 as wetland. enhancement/pond excavation and rain garden construction, can alleviate the 274 stress on the existing system; reduce the threat of flooding, while also improving water 275 quality. By creating additional storage- to reduce the risk of flooding, it is anticipated that 276 the street flooding will also be reduced.. Creating upstream storage will reduce the amount 277 of water that reaches the dual pipe, and the timing of the water reaching the dual pipe will 278 also be more staggered, alleviating street flooding even further. 279 Action to Date: 280 This subwatershed was added as a problem area in 2007.. 281 282 Recommended 2009 action: 2$3 In order to create the additional storage recommended in the report, a final project needs 2.84 to be designed. We have hired WSB and Associates to complete the following work: 285 • Additional study. The pond. that was constructed as a part of the Midland Hills 28b Condominium development, which. may have additional capacity than is currently 287 being used. Analysis would be completed to determine how much storm water could 288 be redirected to the pond and what improvements would be needed to da so. City of Roseville 2008 Storm Water Annual Report Page 8 of 14