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Mounds View Stormwater Pond Assessment <br />3 RESULTS <br />July 2023 <br />Sediment accumulation percentages and years to date (based on the sampling year of 2022) since the <br />basin was constructed are summarized in Table 3-2. The sediment accumulation rate was compared to a <br />benchmark value of 3% per year as a frame of reference to understand how quickly (or slowly) the basins <br />are filling with sediment. This value is an anecdotal metric based on historical basin sedimentation <br />surveys from across the Twin Cities Metro. <br />The sediment accumulation rates per year were used to determine the estimated dates when the ponds <br />will reach 50% sediment accumulation. The pond sediment accumulation rate was calculated by using the <br />sediment accumulation percentage and dividing it by the number of years since the basin was last <br />dredged or constructed. The estimated cleanout year was calculated by using the sediment accumulation <br />rate and determining how many years it would take the basin to reach a sediment accumulation of 50%, <br />assuming a fixed rate. If the time to cleanout was greater than 10 years, it was given a 2032+ value. <br />These calculations are only for planning purposes, as they are based on only one sediment accumulation <br />data point. As the City revisits these ponds in the future, it can improve this calculation with more data <br />points to get a more accurate picture of the pond sedimentation rate. <br />16 <br />