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SECTION 2 Surface Water Management Plan Section 2: Land and Water Resource Inventory City of Arden Hills WSB Project No. 3455-200 Page 10 into Little Johanna Lake and subsequently outlets into Lake Johanna. Ramsey County Ditch 4 flows from the south end of the City towards the northwest. 2.3.2. City-maintained Drainage Systems The existing drainage system for Arden Hills is shown in Figure 7. The system consists of various city-maintained catch basins, piping conveyances, and constructed stormwater ponds. Drainage systems are evaluated, installed, upgraded, and maintained as feasible and practical on a project-by-project basis. Evaluations for new projects are conducted during yearly CIP planning cycles. 2.3.3. Inter-Community Flows Three points of discharge from the City of Arden Hills into other municipalities have been identified by the RCWD as part of district-wide modeling finalized on February 24, 2012. These points of inter-community discharge as well as their associated peak flow rates are identified in Table 2-7 and in Appendix F. These flows have been established by RCWD as benchmark flow rates based on current land use. Through its goals and policies as well as deference to RCWD rules, the City will regulate to either maintain or reduce flow rates relative to the established benchmarks. RCWD is continuously updating the district model. Any significant outcomes of the model may need to be addressed in Arden Hills’ plan. Table 2-7 Benchmark Inter-community Flow Rates Receiving City Watercourse Peak Flows (cfs) 2- year/24- hour Rainfall 10- year/24- hour Rainfall 100- year/24- hour Rainfall 100- year/10- day Snowmelt Mounds View Rice Creek 225 460 761 1377 New Brighton Lake Johanna Outfall 40 72 96 109 Shoreview RCD 1 Main Trunk 3 9 12 29 2.4. Hydrologic Modeling There are 13 proposed potential regional ponds in Arden Hills that were identified in a 1999 comprehensive drainage study by BRW Inc. TCAAP property was not considered or modeled as part of this plan. Two ponds on TCAAP property were completed as part of the reconstruction of Highway 96. Conceptual HydroCAD modeling was completed for the remaining eleven proposed regional ponds. The hydrologic modeling effort quantifies the 5-, 10-, and 100-year, 24-hour design storms using antecedent moisture conditions. The 100-year design storm was used to calculate the peak height of each pond and to determine if any potential damage or flooding could occur in neighboring structures. Stormwater quality and treatment modeling was undertaken using the P8 Urban Catchment model. The ponds were designed to meet Nationwide Urban Runoff Program (NURP) standards, which are removal of 90 percent of total suspended solids (TSS) and 65 percent of total Dr a f t 11 / 2 0 / 2 0 1 7