2007-01-23_PWETC_AgendaPacket - Laserfiche WebLink

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The following table shows pond elevation data, accompanied with the storm water elevations produced from the XPSWMM models for Charlie Pond (C Pond), the pond north and east of Charlie Pond (NE Pond), the pond north and west of Charlie Pond (W Pond), and AD I during the 2, 10, and 100 year rainfall events. Elevations for these areas were reviewed in order to determine whether the volume of the pond is adequate for the drainage areas flowing to them. LOCATION 1. C Pond 2. NE Pond 3. WPond 4. ADI NWL SPILL CREST 2-YR-WL 894.00 909.00 894.67 906.54 908.79 907.46 901.68 905.02 903.25 902.00 904.00 904.53 10-YR-WL 896.44 908.82 905.10 907.27 100-YR-WL 897.80 909.06 905.15 910.45 The analysis of the W, NE, and C ponds are considered together because the Wand the NE pond drain to Charlie pond during more intense rain events. Focusing on Charlie Pond, even in the 100-year event, Charlie pond does not rise to an elevation that would go over the spill crest. This tells us that Charlie Pond has adequate volume to handle all the drainage areas flowing to it, including the two newer ponds. Area AD 1 needs to be analyzed separately. Model results indicate that water ponds in this area during all rain events. The 100-year rain event also showed an elevation that is very close to some of the historical data provided, which continues to indicate that the model is producing results that accurately represent the Charlie Pond watershed and the AD I sub-drainage area. Appendices A-I, A-2, and A-3 provide a further summary of key physical and hydrologic data for the 2, 10, and 100 year rain events produced by the XPSWMM existing conditions model for the Charlie Pond Watershed. SUMMARY AND ANALYSIS OF POSSIBLE SYSTEM IMPROVEMENTS During the process of setting up the XPSWMM existing conditions mndel, the City of Roseville requested some additional modeling to review possible improvements that could be made to the storm sewer system. After the existing model was complete, these additional scenarios were set up, run, and analyzed. The description and results of these mndels for the 100-year rainfall event are summarized below. The alternative scenario models were all run with the 100-year rainfall event only and include three main storm sewer system adjustments; eliminating the storage associated with the AD 1 drain and creating a swale that sends the water directly to Brenner, adding an inlet to MHI05 (currently a closed manhole at the comer of Millwond and Brenner), and providing an overflow connection between MHCBN to MHI03 (at the Millwood South low point). Also mndeled was the possible comhination of these improvements in conjunction with one another. The fourth scenario, modeled as a separate case, was to change out any inlet castings that allow only 1.4 cfs maximum to castings that allow 1.5 cfs maximum. The fifth scenario, also modeled as a separate case, disconnects CB 1, CB 2, and CB 3 in the Millwood South low area and sends water directly to Lake Owasso instead of to Charlie Pond and then back to Lake Owasso. Flooding depths (based on weighted average by drainage area) for the three residential areas identified above during the 100 year rainfall events are as follows: 1. Eliminate storage at AD 1 LOCATION 1. Millwood South - Low Poiut 2. Millwond - Brenuer Intersection 3. A vou - Low poiut (Charlie pond elevation = 898.50) 100-YR-DEPTH 1.98 ft 1.04ft 1.95 ft Existing 1.98 ft 0.85 ft 1.95 ft 2. The addition of an inlet at MHI05 LOCATION 1. Millwood South - Low Point 2. Millwood - Brenner Intersection 100- YR-DEPTH 1.93 ft 0.84ft Existing 1.98 ft 0.85 ft 40f6