06-03-09 Drainage and Flooding Committee minutes

Browse Search

The design capacity of a storm sewer system is based on the water surface elevation in the receiving drainage channel and is considered the starting water surface elevation for calculating the hydraulic grade line (HGL) elevation along the pipe network. It is common engineering practice to set the starting water surface elevation at the top of storm pipe. The existing storm sewer capacity was analyzed based on a top of pipe starting water surface elevation of 14.69 (NA VD 88, 2001 Adj.) and invert elevation of 9.69 (NA VD 88, 2001 Adj.). Exhibits 3, 4 and 5 is a ponding analysis that shows excess runoff cannot enter into the storm sewer system. An inadequate number of inlets can cause this, the inlet capacity may not be enough, or it could be due to an undersized storm sewer system. Increases in ponding elevation are in 6-inch increments. When ponding depth approaches I8-inches over the top of the curb, or inlet, areas that become inundated show some consistency with repetitive loss data. Ponding elevations very from street to street based on runoff instead of tail water backing up into the system from the channel. 2.5 Alternatives Evaluation Alternatives evaluated include adding a storm sewer trunk line in addition to the exiting storm sewer trunk to double capacity, replacing the existing trunk line with pipe for more capacity and replacing or adding partial storm sewer improvements. In addition to storm sewer improvements, roadway profile modifications were investigated either in combination with storm sewer improvements or completely independent. Improvements evaluated include: 1. Add Storm Trunk Parallel to Existing Trunk with Pavement Repair - Add an additional storm sewer trunk line with additional inlets along the northbound side of Fleetwood Drive and parallel to the existing trunk line from South Sycamore to the 2-4 Klotz Associates Project No. 0127.009.000 May 2009 Fairmont Park East & Brookglen Drainage Study City of La Porte