CE 374 K Hydrology Second Quiz Review Daene C. McKinney Runoff Processes Atmospheric Moisture Watershed Terminology Concepts Streamflow Components of hydrologic cycle affecting it Snow Rain Evaporation Interception Energy Throughfall and Stem Flow
Snowpack Snowmelt Watershed Boundary Pervious Surface Impervious Infiltration Soil Moisture Percolation Groundwater Evapotranspiration Overland Flow Groundwater Flow Streams and Lakes Channel Flow Runoff Evaporation Hydrographs Basin Lag Centroid of Precipitation Peak Lim b Lim b
Risi ng n sio Discharge, Q s ce Re Time of Rise Inflection Point Baseflow Recession Baseflow Recession Beginning of Direct Runoff End of Direct Runoff Time Baseflow Separation Three techniques Straight line method Fixed Base Method Variable Slope Method
N A0.2 Discharge, Q Discharge, Q Discharge, Q Direct DirectRunoff Runoff D Direct Runoff A E A C A Baseflow C Baseflow Baseflow B B B Time Time Time Abstraction (Losses) Estimation
Phi Index Method M rd Rm t m 1 12000 0 t=0.27 0.5 10000 n 1 8000 t Qn A rd depth of direct runoff Rm observed rainfall Phi index M # intervals of rainfall contributing to driect runoff t time interval 1 1.5 2 2.5 Streamflow (cfs)
V rd d A N 6000 4000 2000 0 7:30 PM 9:00 PM 10:30 PM 12:00 AM Time 1:30 AM 3:00 AM 4:30 AM 6:00 AM Abstraction (Losses) Estimation SCS Curve Number Method 1000
S 10 CN Pe 0.2 S 2 P 0.8S P Pe I a Fa Precipitation Pe P Ia Fa tp I a 0 .2 S Fa S (P I a ) (P I a S ) Time P Total Rainfall Pe Rainfall Excess I a Initial Abstraction Fa Continuing Abstraction S Potential Maximum Storage
Hydrologic Measurement Climate Precipitation Surface Water Flow Stage Rating Curve Unit Hydrograph Time Area Relationship D C Q1 P1 A Q2 P2 A P1B B Excess Rainfall Q3 P3 A P2 B P1C Q4 P4 A P3 B P2C P1 D A Q5 P5 A P4 B P3C P2 D P3
P1 P2 P4 P5 G Q6 0 * A P5 B P4C P3 D Q7 0 * A 0 * B P5C P4 D Q8 0 * A 0 * B 0 * C P5 D Time, t Unit Hydrograph Derivation n Qn PmU n m 1 m 1 Q1 P1U1 Q2 P2U1 P1U 2 Q3 P3U1 P2U 2 P1U 3 Q4 P3U 2 P2U 3 P1U 4 Q5 P3U 3 P2U 4 P1U 5 Q6 P3U 4 P2U 5 P1U 6 Q7 P3U 5 P2U 6 P1U 7 Q8 P3U 6 P2U 7 P1U 8 Q9 P3U 7 P2U 8 P1U 9 Reservoir Routing
Storage 2S Q, and Q t Discharge Relationship Level Pool Routing 2 S j 1 Q j 1 t 2S I j 1 I j tj Q j I j 1 I j 2Stj Q j 2Sjt1 Q j 1 2S j 1 Q j 1 Q j t
2 S j 1 2S j Q j 1 2Q j Q j t t River Routing Muskingum Method Prism Storage Wedge Storage S K [ XI (1 X )Q] Q j 1 C1I j 1 C 2 I j C3Q j t 2 KX 2 K (1 X ) t t 2 KX C2 2 K (1 X ) t 2 K (1 X ) t C3
2 K (1 X ) t C1 SCS Dimensionless Hydrograph SCS developed a parametric UH model based on averages of UHs from a large number of small agricultural watersheds in the US. A watershed area C conversion factor for unit system Tp- time to peak t excess precip duration tlag - basin lag, time between center of rainfall excess and UH peak Given ER hyetograph and time lag, then solve for time of UH peak, then UH peak U p C A Tp
Tp t tlag 2 Frequency Analysis Recurrence Interval Return Period: Average recurrence interval Probability of an extreme event is related to the return period Time between ocurrences of X xT E ( ) E ( ) T 1 p Extreme Value Distributions
EV-I, EV-II, and EV-III Extreme Value Type I (Gumbell) Distribution F ( x) exp exp y y T yT ln ln T 1 x u 6s u x 0.5772 xT u yT Frequency Factors In general xT x KT s xT Estimated event magnitude KT Frequency factor Normal K T zT
EV-I K T LP-III: See table xT x zT s T Return period x Sample mean s Sample standard deviation 6 T 0.5772 ln ln T 1 Hydrologic Design Depth-Duration-Frequency Estimates TP-40, Hydro-35, Asquith
I D F Curves i c Td e f i a t bc Design Hyetographs: distribute rainfall over time SCS Hyetograph Triangular Hyetograph Alternating Block Method
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