07-09-2003 Council Agenda - Laserfiche WebLink

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Maple Leaf Court We reviewed the drainage calculations prepared by Ken Gust Enterprises for Canada Woods West (Maple Leaf Court). The calculations are based on the rational method and show no increase in the peak discharge rate. Due to advancements in storm drainage software and as a check to the original calculations completed, the site was then modeled based on the SCS method using HydroCAD. This new method indicated the peak discharge was slightly increased by 1.35 cfs from existing to proposed. While there was an increase, the net effect of the development on the downstream system appears to be negligible with this slight increase. As you are aware we completed improvements to the drainage swale adjacent to Maple Leaf Court in August 1999. The project included the stabilization and reinforcment of the existing swale to protect against further erosion from the existing storm water flow. The largest contributors of storm water to the swale are County Road D, LaBore Road, and the High Crest Apartments in Vadnais Heights. Both Labore Road and County Road D are rural sections using road ditches as the means of storm water conveyance. While improvements such as bituminous paving have been made to both streets since their original construction, there is no record that the storm water patterns have been revised. The City of Vadnais Heights was contacted regarding the High Crest Apartments, and while no specific records were found it was determined that they were constructed in 1969. This date is prior to the beginning of the wetland and /or storm water regulations of 1975. Therefore at the time of construction, standard practices were used and no wetland or drainage laws or regulations were broken. It should be noted that the City is currently exploring options with the Minnesota Department of Transportation, Ramsey County, and Vadnais Heights to divert drainage from along County Road D, the area north of County Road D, and LaBore Road to the interstate as part of the Unweave The Weave project. Any plan for diversion of stormwater and a reasonable cost sharing agreement for its completion would need to be approved by all three agencies listed along with the City of Little Canada prior to any construction. Conclusions Although it does look as if minor changes to the drainage patterns occurred due to the development within the City of Maplewood and the construction of the earthen berm, the construction does not appear to prevent the area to the northwest from draining. The ditch along the westerly berm edge was constructed to maintain drainage of the property to the northwest and calculations indicate it has sufficient capacity to do that. It is possible that growth within the ditch may be adversely affecting it design capacity. We recommend that the ditch be cleaned and maintained to the extent allowed by the Ramsey Washington Watershed and the Army Corps of Engineers. As it exists, the Maplewood storm water pond is designed to handle the drainage area flowing to it and provides adequate water quality treatment. Opening of the north end of the berm or installation of a pipe from the west would negatively impact the efficiency of the storm water pond and actually increase the amount of water that drains west of the berm. Therefore no changes should be made to the earthen berm or the storm water pond it creates. C: \WINDOWS \Temporary Internet Files \OLKF1A3 \Sculley Drainage Findings.doc 5