12/10/2003 P&Z Packet - Laserfiche WebLink

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• Eagle Brook Church Review Page 4 December 4, 2003 City of Lino Lakes, Minnesota has been verified to exist. This ditch drains property well beyond the church site itself, or an area of 590 -650 acres to the south and east of the site according to available records. It is proposed to maintain the ditch in a pipe condition and re -route it around the church site. As shown on the plan, an 18 -inch diameter RCP pipe is proposed to connect from the existing drain tile, run westerly along the south property line a distance of about 1100 feet, turn northward and flow to an existing ditch and wetland area. The existing flow capacity of the ditch must be maintained. Therefore, hydraulic calculations must be submitted to the City for review to assure that the existing flow capacity is maintained or exceeded. Additional drainage and utility easements will also be required (provided on the Preliminary and Final Plats) to provide perpetual maintenance. The drain tile running into the property further west (1200 feet west of County Road 21) is also shown connecting to the proposed 18 -inch pipe. At this location, it also appears that much of the surface water runoff from properties to the south flows into the Eagle Brook property through a natural low area or swale. The proposed grading plan appears to raise the ground level at the property line and cut off the overland drainage. It is suggested that the storm sewer and grading be designed and/or adjusted accordingly to assure that grading changes on the Eagle Brook property do not result in adverse impacts to the existing drainage patterns of neighboring properties. Again, hydraulic calculations must be submitted to assure that the existing flow capacities are maintained or exceeded. Based upon the information provided, there will be no increase in the developed rate of runoff from the site. A summary table has been provided showing that runoff rates for the 2 -year, 10 -year, and 100 -year storm events show significant decreased in the runoff rate from the site under the proposed site conditions. However, full drainage calculations must be submitted to the City to verify the summary figures provided. Best management practices (BMP's) have been incorporated into the site design to limit and control the rate of runoff, and provide storm water treatment per RCWD requirements. The information provided states that County Road 21 drainage and runoff shall be maintained in its current operative state which includes discharge through vegetated swales to existing wetland areas. However, the grading plan provided is not entirely clear as to where the roadway ditch drainage will flow, especially with pending turn lane improvements and widening of the roadway. It would appear from the plan that the north part of the roadway will drain to an existing wetland at the north end of the site as it currently does. The ditch at the south end of the property appears to connect with the County Ditch 72 system, but the grading plan is not entirely clear. There is no filling and/or impact to existing wetlands or flood plain proposed. Existing woodlands and buffer areas adjacent to Peltier Lake are proposed to be left naturally as is. In addition, dedicated wetland buffers are shown on the Preliminary Plat. The site grading plan also proposes to incorporate effective use of stormwater retention and infiltration methods to control runoff, provide stormwater treatment, and enhance groundwater infiltration in accordance with RCWD requirements. Bioretention areas in the proposed parking lots and rain gardens are proposed in the design to assist in meeting RCWD requirements for rate control and stormwater treatment. Further construction details must be provided on the plans. In addition, it is recommended that groundwater levels at proposed infiltration basin locations be verified to assure the effectiveness of infiltration at those locations.