Detention Pond and Channel Stabilization for Bartholomew Park Tanya Hoogerwerf, Sara Poindexter, Travis Wilson and David Kracman December 13, 2001

Outline Watershed deliniation HEC-HMS network Pond design Downstream channel improvements System performance for design storms

Watershed Deliniation 2.2 acres P2 12.3 acres P1 7.5 acres

HEC-HMS Network

Pond Design Pond Width 150 ft Pond Length Side Slope 3:1 Spillway Elevation 6 ft Spillway Length 30 ft Orifice Plate Elevation 0 ft Orifice Plate Area 1 ft2 Culvert Elevation 2 ft Culvert Diameter

Downstream Channel Improvements PARAMETERS Channel width = 5 ft Longitudinal slope = 0.1 Angle of repose = 40 Side Slope 2:1 25-year design flow = 30 cfs RESULTS d50 = 8 inches d20 = 4 inches d100 = 16 inches Flow depth = 0.56 ft Flow velocity = 10 ft/s

System Performance – 25-year Flood Peak Inflow: 73.5 cfs Peak Outflow: 33.2 cfs Peak Storage: 3.2 ac-ft Peak Elevation: 5.2 ft

System Performance – 100-yr Flood Peak Inflow: 95.7 cfs Peak Outflow: 56.4 cfs Peak Storage: 4.0 ac-ft Peak Elevation: 6.2 ft

Performance – Water Quality 2-year Return Period Storm Calculated Detention Time of 9 hours Below Normally Recommended Time Solution – decrease low-flow orifice area Possible health benefits from lower detention time?

Questions?