Agenda - Council - 07/11/2023 - Laserfiche WebLink

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2019 Municipal Plaza and Center Street Concept Stormwater Reuse 06/26/2019 Page: 4 Additional Considerations A simplified estimate of stormwater runoff expected from the street section was assembled to ensure the watershed can produce enough runoff to adequately fill the tanks. Table 1 is a summary expected runoff volumes for a variety of events. A rainfall event producing between 3.6 and 4.3 inches in 24 hours (5-year to 10-year return interval) can completely fill the tank. Table 1: Summary of expected runoff volumes. Rainfall Even PRainfall Depth Runoff Runoff 111 (IN) Volume (CF) Volume (GA) 1" Event 1-Year 2-Year 5-Year 10-Year 1.00 2.46 2.86 3.58 4.26 5,500 14,700 17,600 22,700 27,500 41,140 109,956 131,648 169,796 205,700 During final design, additional hydraulic information will be provided to provide an effective high flow bypass system. In other words, if the tank is full and the City experiences a 100-year rainfall event, there will be adequate bypass capacity to reduce local flooding and protect the tank(s). Also, since the COR trunk storm sewer system is already designed to accommodate a 100-year rainfall event with discharge to regional flood storage areas, the bypass system will effectively mimic the originally designed scenario. In between events when irrigation is occurring, or the tanks is being filled, there will be hydraulic relief on the trunk system and volume control provided. Since the reuse water will pass through a filter and UV treatment system, the impact to groundwater resources through the infiltration of irrigation water is expected to be very minimal. Impacts to groundwater resources in the ERA are not anticipated. Sincerely, Bolton & Menk, Inc. Timothy J. Olson, PE, CFM Water Resources Project Manager