08/08/2007 P&Z Packet - Laserfiche WebLink

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Moon Marsh Drainage Calculations Review • City of Lino Lakes, Minnesota August 3, 2007 06/19/07 It appears that the emergency overflow for wetland No. 1, at the north end of the site, is located at the low point of the proposed road at station 19 +00. The new overflow created by the construction of the road appears to be at a higher elevation than the overflow elevation for this wetland under existing conditions. Identify the overland emergency overflow elevation for wetland No. 1 located at the north end of the site on the Plan and ensure that the low opening of the existing home located north of the site is a minimum of 1 foot above the new emergency overflow elevation. Label the emergency overflow elevation for wetland No. 3 and wetland No. 4 on the Grading Plan. 08/03/07 Since the proposed emergency overflow elevation of 889.3 for the north wetland #1 is 0.70 - inches higher than the existing overflow elevation of 888.6 for wetland #1 as labeled on the Grading Plan, verify that the lowest opening of the existing structures located to the north of the site is a minimum of 1 foot above the proposed overflow elevation of north wetland #1. 4. The sum of the total wetland area defined in ponds 10P and 12P of the model should equal the wetland area of the existing wetland defined in pond 11P. For example, the area of the wetland at elevation 888 under existing conditions in pond 11P is 10.1 acres; however, the sum of the area at elevation 888 under proposed conditions for ponds 10P and 11P is 17 acres. 08/03/07 The available storage for existing wetland #1 (pond 11P) is less than the available storage for wetland #1 under proposed conditions (pond 10P and pond 12P) in the model. The available storage for wetland #1 under proposed conditions should be equal to or less than the available storage for wetland #1 under existing conditions. Update the proposed conditions model to reflect actual site conditions. 5. The filtration basin 2P and 4P outlet device routing is not consistent with the outlet structure detail on Sheet 7. The 12 inch horizontal orifice /grate should be routed through a 12 inch diameter outlet, not the 4 inch diameter pipe as currently modeled. In addition, the 4 inch outlet should be a 6 inch outlet at a 0.0% slope, with the length as labeled on the Grading Plan and outlet structure detail. Update for consistency. Runoff rates will be checked when the revised model is submitted for review. 08/03/07 Based on the Grading Plan and outlet structure detail, the 12 inch horizontal orifice /grate should be routed through a 12 inch diameter outlet, not the 6 inch diameter pipe as currently modeled. Runoff rates will be checked when the revised model is submitted for review. 6. Identify the HWL and location and elevation of the emergency overflow for all culverts on the Plan. Low floors are required to be 2 feet above the 100 -year elevation of all culverts. 08/03/07 It appears that the emergency overflow for the upstream end of the culvert crossing located at station 15 +40 is at an elevation of approximately 890. Label the emergency overflow location and elevation of this culvert. Label the HWL of pond 5P and pond 6P on the Grading Plan. Use the existing culvert length and invert elevations for the outlet of wetland No. 1 in the existing conditions model. 13810.002