4.4 SR 10-17-2022 - Laserfiche WebLink

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Option 1: Do Nothing Through modeling it has been determined that the storm sewer system is meeting spread requirements on a 10-year storm event. This is the standard storm sewer sizing used to design the pipe sizes and number of catch basins needed to prevent a safety issue for drivers on 10-year or smaller storm events. When rarer storm events occur, or flash flood downpours, it is by design that all sized storm events do not make it into the storm system and flash flood all downstream outlets. Given that this localized low point doesn't have a standard emergency overflow preventing property damage, this option may not be preferred. Option 2: Pipe Upsize and Storm Water Mitigation. Option 2 considers the limited pipe capacity under Main St. Upsizing the pipe from a 12" pipe to a 21" pipe across Main Street and 280' south along Morton Avenue to the existing 18" pipe. This eliminates the bottle neck in the system to handle larger storm events (25- year and higher). The upsize alleviates surcharging conditions at the low point on Morton Ave but this option also proposes to add double catch basins at the low point to increase the rate that the larger storm events need to flow into the storm sewer system to prevent flooding. As this option relieves the flooding condition at the low point, it moves more water down to the ultimate discharge point. To prevent higher flow rates at the discharge point, a surge pond or perforated pipe is needed to mitigate the flows. The storm sewer reconfiguration also adds one new catch basin in the northwest quadrant of Main St and Morton Ave to reduce overland bypass flow to the north. A second catch basin at the northeast corner of Main St and Morton Ave was considered but provides no additional flood relief at the low point. Option 3: 319 Morton Avenue Surge Pond & Main Street Intersection Improvements This option considers the fact that the garage and home at 319 Morton Avenue currently sit below the emergency overflow (EOF) point of the identified low point on Morton Avenue. If the home were to be removed, no homes would fall below the EOF. As an additional improvement to the storm system, double catch basins could be added at the low point and a surge pond could be built at the location of the current home to help relieve down stream impacts. This option also includes replacing the undersized 12" storm sewer pipe across Main Street to eliminate the continuing maintenance issue that is occurring with such a flat shallow pipe. Flooding Depths Table 1 describes the low point, top of curb, and emergency overflow (EOF) elevations at the low point on Morton Ave. A typical storm sewer design would provide capacity for 10-year rain fall event such that the 10-year storm is contained within the storm sewer pipe and the gutter spread is managed to half of the drive lane to avoid hydroplaning. Table 2 describes the existing and proposed conditions depths in Morton Ave. Based on traditional design standards, the current catch basin configuration can manage the 10-year storm. The 25-, 50-, and 100-year storms start to threaten the adjacent property by overtopping the curb and utilizing the EOF. The proposed options increase the storm sewer system to take storm events larger than the standard 10-year event, to mitigate the flooding issue identified during extreme storm events. Prepared by: Bolton & Menk, Inc. Proposed Flooding Solutions Morton Avenue Drainage Study I OR11.127809 Page 4