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libHydro
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LibHydro LibHydro in Excel LibHydro in ArcMap
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LibHydro in Excel Functions list that is called by Excel VBA
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LossGreenAmpt The Green and Ampt model computes the precipitation loss on the pervious area in a time interval as: L(t) Moisture Content Φ θe θr θi Δθ ft Li ft: Infiltration Rate (L / T) K: Hydraulic Conductivity (L/T) Ft: Cumulative loss at time t (L) Sf: Wetting Front Suction Head (L) ΔΘ :Moisture Deficit (-) Φ: Porosity (-) Θi: Initial Moisture Content (-) Li: START INITIAL LOSS L(0): START INFILTRATION L(END): FINAL INFILTRATION
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LossInitialConstant Basic Concept for LossInitialConstant
Et = Et (Impervious) + Et (pervious) Et (Impervious) = Pt Et (pervious) = 0 if ΣPt < Ia Pt – fc if ΣPt > Ia and Pt > fc 0 if ΣPt > Ia and Pt < fc Et : Excess at time t Pt : Precipitation at time t Ia: Initial Loss fc: Constant Loss Rate
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LossSCSCurveNumber Pe = Accumulated precipitation excess at time t (mm) P = Accumulated rainfall depth at time t (mm) Ia = Initial abstraction (initial loss) (mm) S = Potential maximum retention (mm) (For SI Unit) CN = Curve number (30 < CN < 100)
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Unit hydrograph Precipitation (mm) Loss Rates (Green Ampt, Initial
Unitgraph Size Unitgraph (Snyder, SCS or Clark) Unitgraph Convolution Loss Rates (Green Ampt, Initial Constant or SCS Curve Number Excess (mm) Unit Runoff (m3/s per mm of excess) Runoff (m3/s) Precipitation (mm) # of unitgraph ordinates
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Unitgraph Clark Parameters Process of the Unitgraph Clark
Time of Concentration: The time of flow from the farthest point on the watershed to the outlet Storage Time: Storage constant R with the linear reservoir model St = R*Ot Process of the Unitgraph Clark 1. Estimate the contribution area with 2. time-area relationship 3. Calculate the average inflow It to the storage at time t 4. Calculate the unitgraph ordinates with the following equations
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Snyder’s Unit Hydrograph
Input Variables tp : Snyder Lag (hr) Cp: Snyder Cp A: Basin Area (km2) tR: Time interval Output Variable: unitgraph ordinates (m3/s per mm of excess) tpR=tp-(tr-tR)/4 (when tpR≠5.5tR) Standard UH (when tpR=5.5tR) tr tR tp tpR qP=2.75*Cp/tp Discharge per unit area Discharge per unit area qp qpR qPR=qP*tp/tpR W75 W50 tb Time Time
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SCS Dimensionless Hydrograph
qp: Peak runoff (m3/s) C:2.08 for SI A: Basin Area (km2) Tp: Time of rise tp Tr/2 Tr tb Tp Excess Rainfall Direct Runoff qp Tr: Excess Duration (hour) Tp: lag time (hour) Tc: Time of concentration (hour)
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BaseflowHEC1 total flow > recession threshold at falling limb
or total flow is at rising limb Qb: base flow Q0: initial base flow K: recession constant T: time Time Discharge Total flow recession threshold Qt: total flow Qr: flow where recession starts tr: time when recession starts (B) total flow < recession threshold at falling limb Baseflow
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Muskingum Routing Prism Storage Wedge Storage St: Storage at time t
It: Inflow at time t Ot: Outflow at time t K: Muskingum K X: Muskingum X
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Muskingum Routing Feasible region for Muskingum model parameter X 2 1
0.5 1.0 X Feasible region
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EarthDistance in ArcMap
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LibHydro in ArcMap
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Model Builder Input Box for LossInitialConstant
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Loss Initial Constant
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Model Builder Input Box for Snyder Unitgraph
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Snyder Unitgraph
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Model Builder Process
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