5.5. SR 08-06-2007 - Laserfiche WebLink

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The plan serves as a planning tool for future trunk storm sewers and ditch conveyance, ponds, basic nor- mal levels, lOa-year flood levels, and building elevation requirements. We addressed water quality issues regarding NPDES regulations, water quality enhancement, future ponding area aesthetics, and trout stream issues. In addition, Barr provided the city with electronic fIles for the complete hydrologic and hydraulic analysis of the city, including field verification of map-determined watershed divides, full development watershed conditions modeling for lO-year and lOa-year frequency storm events, and a summary of all work on GIS figures and Quattro Pro tables. Surface-Water Management Plan City of Hastings, Minnesota Barr prepared Hastings' first surface water management plan and numerous updates as the city has continued to develop and expand. One of the updates involved what is known as the Hastings South Fringe Area (SFA) that petitioned and was annexed into the city. This annexed area is located south of the Verrnillion River. Through the SFA passes two major drainage-ways that the state has not des- ignated as public waters. Developing a surface water management plan for the SFA required Barr to model a 21-square-rnile agricul- tural watershed outside of the city that drains through the SF A. The hydrologic and hydraulic analysis of the SF A watershed in- volved: ........./v~~ W a) Inventory of all culverts that pass through county or town- ship roads upstream of the SF A. b) Detailed delineation of the watershed's tributary to each road crossing. c) Collection of soil and topography information throughout the watershed. d) Preparation of a hydrologic and hydraulic computer model of the watershed and running it for the la-year and lOa-year storm events. e) Development of a surface-water management plan for the tributary watershed, which identified and prioritized locations where flood control, channel stabilization, channel erosion control, and maintenance measures need to be implemented. Hydrologic and hydraulic modeling was conducted for the 21-square- mile watershed, including the South Fringe Area (shown in blue). A key element of the plan was the realization that the city relies heavily on the upstream system of county and township culverts to provide flow-control regulation. If the county or a township should decide to enlarge the culvert capacity through any road, it could result in significant flooding in the city. Therefore, the surface water management plan calls for the city, Dakota County, and the upstream townships to coordinate any upstream roadway and culvert improvements to ensure the city's newly developing area does not become flooded in the future. Barr Engineering Company Page 17