10-13-25 - City Council Agenda - Laserfiche WebLink

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Ms. Katie Larsen 10/03/2025 Page 5 Erickson Property Development - Engineering Review Pre- and Post- Development Discharge Rates (cfs) Condition 2-Year 10-Year 100-Year 10-Day Snowmelt Existing 9.64 15.23 32.09 Only needed if basins landlocked Currently Proposed 4.31 6.46 12.40 Only needed if basins landlocked Comments: 1. This development falls within the Northeast Drainage Area Comprehensive Stormwater Management Plan (CSMP) area and as such is beholden to additional rate control and volume reduction requirements. Landform Response (8/11/25) – Proposed outlet structure has been re-routed to the existing south pond (Pond 500). See updated plans & stormwater report. 2. The pond south of this development was constructed with the Watermark development and designed to include runoff from the Erickson Property. If rates are reduced or maintained from existing conditions, volume control provided in the form of stormwater reuse, and water quality treatment provided by the proposed pond, it is recommended to overflow the onsite pond south to the existing Pond 500 (NWL 899, HWL 904.3). This allows the proposed development to meet CSMP rate control requirements by utilizing the existing Watermark system that already meets requirements. Landform Response (8/11/25) – Proposed outlet structure has been re-routed to the existing south pond (Pond 500). See updated plans & stormwater report. 3. Why does PB-3 have water surface land cover modeled in HydroCAD? Landform Response (8/11/25) – This should have been Type D soils. Updated. 4. The pond EOF must include riprap stabilization. Landform Response (8/11/25) – Updated. See Plans. 5. The modeled pond EOF of 906.5 does not reflect the EOF of 905.57 in the plans. Landform Response (8/11/25) – Model has been updated with an EOF of 905.57. 6. A detail must be provided for the pond outlet control structure. Landform Response (8/11/25) – Plan and profiles have been included. WSB Response (9/3/25) – The pond skimmer structure must include the rim elevation and must match the grate modeled in HydroCAD. The submerged 12” pipe is recommended to have an invert of 900 to ensure it remains submerged when the pond is drawn down for irrigation. Landform (8/11/2025) Pond skimmer has been updated in modeling to be at a rim elevation of 908.0 in order to match the plans. 12" pipe has also been lowered to elevation 900. See detail 1 on sheet C7.4. Also see sheet C3.1 and sheet C5.1. WSB (9/26/2025) Complete 7. The 10’ aquatic bench should continue around the entire pond. If that is not feasible, the bench should at least be on the eastern side of the basin to provide a safety bench for residents. Landform Response (8/11/25) – Aquatic bench has been moved from western side to eastern side of pond. Page 124 of 145