LAR 512 - Fall 2002

LAR 512 – Fall 2002

PROBLEM #14 – WETLAND INFLOW & OUTFLOW ANALYSIS

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Download a copy of TR-55, Urban Hydrology for Small Watersheds and then load TR55_210.EXE . Then select 1 – Help to Select Method and enter, answer yes to first two questions and no to the third question to obtain Graphic Method and hit F2, read and page down. Now enter user number “1”, project name “Wetland Inflow Analysis”, county “Wake”, state “NC”, drainage area “235” acres, runoff curve number “85”, time of concentration “0.5” hours, and page down. Now enter rainfall type “II”, storm 1 enter “2” year frequency and enter “3.6” inches, storm 2 enter “10” year and “4.8” inches, storm 3 enter “25” year and “5.6” inches, storm 4 enter “50” and “6.5” inches, storm 5 enter “100”year and “7.0” inches, and then hit F7. This will provide an estimated inflow to the basin for each of the storm events. Hit F2 for a print out of the results.

Now select 5 for Tabular Hydrograph Method, and enter. Page down and enter tabs, use type “II” rainfall, “100” year frequency, constant “7.0” inch rainfall, and yes to last question. Page down and enter subarea name “Basin”, drainage area “0.367” sq.mi., runoff curve number “85”, time of concentration “0.5” hours, travel time “0.5” hours, and 24-hour rainfall “7.0” inches. Hit F7 and write down times in hours with corresponding inflow rates, cfs into the basin. Plot these on a graph to create an inflow hydrograph.

Now select 6 for Storage Volume for Detention Basins, enter, read, and page down. Enter “0.367” sq.mi., type “II” rainfall, “100” year frequency, “5.25” inches of runoff and “1020” cfs peak discharge both from Graphical Peak Discharge Method (item #1 above); put an arbitrary “125” cfs peak outflow from the basin, hit tab, and F7, to obtain a storage volume in acre-feet. Change the peak outflow value incrementally to 250, 375, 500, 625, and 750 cfs and obtain storage volumes for all six values. Plot these values on a graph.

Now select 425 cfs for design of the emergency spillway, set the storage volume accordingly. Assume that the pond was at normal pool elevation (4-feet below the spillway elevation) at the start of the 100-year storm event. Now, compute and plot on your inflow hydrograph, an outflow hydrograph. Outflow will not start until the storage volume has been satisfied. Assume that when outflow starts that 425 cfs is achieved instantly.