CWR4306_Packet_06_master

CWR4306_Packet_06_master - Lecture Packet 6: Estimating...

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Unformatted text preview: Lecture Packet 6: Estimating Peak Runoff Lecture Packet 6: Estimating Peak Runoff Course website: Course website: http://www.ce.ufl.edu/~markn/CWR4306 http://www.ce.ufl.edu/~markn/CWR4306 CWR 4306 – Urban Stormwater System Design CWR 4306 – Urban Stormwater System Design Topics covered in this lecture packet Direct runoff Initial losses Runoff coefficients Travel time Peak (flow) discharge methods Rational Method SCS (NRCS) Curve Number Method Estimating Runoff Estimating Runoff Runoff Hydrograph (flow vs. time) Runoff Hydrograph (flow vs. time) Typical runoff hydrograph (flow vs. time) . Depth of direct runoff (effective precipitation) Depth of direct runoff (effective precipitation) Depth of direct runoff (effective precipitation) Depth of direct runoff (effective precipitation) Terms and definitions Direct runoff -- calculated as effective precipitation Initial losses (abstractions) Interception The capture of rainfall on leaves and vegetation before it reaches land surface. Depression storage Excess water that ponds in surface depressions , and is typically lost to infiltration or evaporation Infiltration (after initial losses) Depending on soil conditions, (if soil is pervious) some water may infiltrate into the ground—groundwater. Evapotranspiration (often neglected for short-duration events) loss of water through evaporation and transpiration Estimating Runoff Estimating Runoff Runoff Coefficients Runoff Coefficients Typically, the amount of runoff corresponding to a given rainfall amount is estimated using runoff coefficients, C. A runoff coefficient is the percent of total rainfall that contributes to runoff. i e = Ci i e = effective rainfall (in/hr) C = runoff coefficient (0 < C < 1) i = actual rainfall (in/hr) Runoff Hydrograph Runoff Hydrograph Time of Concentration and Basin Lag Time of Concentration and Basin Lag Time of concentration (t c ) – time it takes for runoff to flow from the hydraulically most distant point to the point of analysis . Lag time (basin lag) – separation time from the centroid of the excess rainfall to the peak of the runoff hydrograph . Lag time can be thought of as an approximate average of the possible travel times for runoff within a basin. Rainfall and Runoff (Basin Lag Time) Rainfall and Runoff (Basin Lag Time) Relationship between rainfall and runoff. Methods for estimating time of conc....
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This document was uploaded on 10/29/2011 for the course CWR 4306 at University of Florida.

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CWR4306_Packet_06_master - Lecture Packet 6: Estimating...

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