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time of concentration being 7 minutes. 6. For Shoreview drainage areas related to this watershed, the time of concentration was taken from previous models. URS continued with Task #2, the model set-up, by entering all the physical data gathered into an XPSWMM model, recreating the entire watershed system, including the drainage areas, pond volumes, storm sewer pipe, manholes, inlets, outlets, etc. See Exhibit 1 for a map of the Charlie Pond Watershed area showing structure and ponding labels. The hydrologic information identified above is then entered and the model was then run for the three rainfall intensities specified above, the 2-year, the lO-year, and the lOa-year, and the data was analyzed and summarized. The type of information that an XPSWMM model provides inclndes the volume and elevation of water flowing through the system at any point in time during specific rainfall intensitys. XPSWMM gives us the ability to analyze a representative storage area above a manhole or catchbasin ground elevation which indicates flooding. Inlets, manholes, ponds, and wetlands all have a "spill crest" or ground elevation, as well as a representative storage area entered as a physical parameter. The model indicates if and how high the water will rise so if there is a time during a certain rainfall event where the system cannot handle the amount of runoff, the model will produce data showing when, where, and how much. Historically, there have been specific areas of concern within the Charlie Pond watershed: the low point on Millwood A venue south of Brenner Avenue, the intersection of Millwood A venue and Brenner A venue, the low point on A van Street, and the backyards on the west side of Millwood Avenue (specifically the lot just west of 800 Millwood Avenue, which is identified as AD I in the model). There has also been some concern with the function of Charlie Pond in relation to the entire watershed and also with the addition of the two ponds to the north. While the model includes data for every structure and pipe in the system, these areas described above are the ouly spots that show flooding in the model; this corresponds with historical data gathered. Data from the XPSWMM model for these particular areas is summarized below: Existing Conditions Results For the areas of concern within roadways, we looked at the depth of flooding present from the top of the storm sewer castings during a particular rain event. These ponding depths represent a weighted average depth for all the inlets associated with the storm drain system in the drainage area. Flooding depths for the three residential areas identified above during the 2, 10, and 100 year rainfall events are as follows: LOCATION 1. Millwood South - Low Point 2. Millwood - Brenner Intersection 3. Avon - Low point 2-YR-DEPTH 0.01 ft 0.00 ft 0.05 ft 10-YR-DEPTH 100-YR-DEPTH 0.52 ft 1.98 ft 0.14ft 0.85ft 0.89 ft 1.95 ft The existing conditions model set up to run the 2-year rainfall event showed negligible flooding or storage problems at any of the locations indicated above. The results for the lO-year rainfall event showed minimal flooding in the Millwood - Brenner intersection. The other two locations show a flooding depth that is under a foot, which, in most instances, can be considered a manageable depth of flooding depending on the time span. The model indicates that the time to drain the Millwood South low point is between a half hour and an hour, while the time to drain the A van low point is between an hour and an hour and a half, assuming the inlets are not clogged with debris. The lOa-year rainfall event produces flooding close to two feet in depth for the Millwood South area and the Avon low point and drain times of two to four hours, again assuming the inlets are not clogged. The Millwood - Brenner intersection shows less than a foot of flooding and a one to two hour drain time, which can be considered manageable. Depth of flooding is clearly a problem with the 100-year rain event and can be verified by reviewing historical data for these particular locations. These depths provide evidence that show the model is representing the Charlie Pond watershed accurately. 30f6