Washington Street West watershed - City of Champaign

Draft ReportWest Washington Street Watershed Master PlanThe storm sewer junctions displayed in Table 5-2 show the major intersections along theWest Washington Street trunk storm sewer that contain either multiple inflows or largediameter sewers discharging into a manhole along the trunk sewer. The sewer sizes weredetermined by City shapefiles and survey information and were used for sewer area andflow calculations. The pipe capacity columns were determined by calculating themaximum flow possible under gravity flow. The pipe slopes were based on surveyinformation or assumed to be at minimum slope.The inflow sewers at all five junctions shown have an inflow area that is over 15% largerthan the outflow area. This is critical when the sewers are surcharged and subject topressurized flow. The pipe area will control the pressurized flow and with someintersections having inflow pipe areas over 50% greater than outflow sewers, thehydraulic restrictions along the trunk sewer are noticeable. When gravity flow existsduring smaller storm events, the flow capacity dictates the hydraulic restriction in thesewer system. The inflow sewer capacity is usually at or greater than the outlet sewer ateach junction except for the values highlighted in red. These inflow pipe capacities areactually lower than the outflow pipe capacities; however, the inflow sewers are belowminimum slope, which reduces the gravity flow in the sewer. The 27-inch sewer onNorth Russell Street (part of the North Edwin Street Trunk Sewer) was found to be at anegative slope, meaning that ponding at the structure in the West Washington and NorthRussell intersection has to occur before flow is discharged to the West Washington StreetTrunk Sewer. The West Washington Street and North Victor Street junction has an outletsewer with a greater slope and higher capacity; however, the sewer system is typicallysurcharged in this area and rarely flows under gravity conditions for an entire stormevent.North McKinley Avenue: The trunk sewer serving the North McKinley Avenue drainagearea conveys flow from the northeastern portion of the West Washington Streetwatershed. The 36-inch trunk storm sewer discharges to the West Washington Streettrunk sewer just north of the intersection of West Washington Street and North RussellStreet, draining approximately 118 acres. The following junctions occur along thissegment of storm sewer:Pipe Junction LocationWest Bradley Avenueand North McKinleyAvenueWest Eureka Street andNorth McKinley AvenueWest Tremont Street andNorth McKinley AvenueWest Columbia Avenueand North Edwin StreetTable 5-3North McKinley Avenue Trunk SewerDiameter(in)12 and15Inflow SewersArea(in 2 )PipeCapacity(cfs)*Diameter(in)Outflow SewersArea(in 2 )PipeCapacity(cfs)289.8 4.1 15 176.7 2.612, 18,and 18622.0 9.1 24 452.4 9.412 and24565.47 10.9 24 452.4 9.424 and361470.2 34.1 36 1017.8 25.1* Assumes minimum slope for smaller diameter sewers and pipe flowing under gravitySeptember 20095-6Clark Dietz, Inc.