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Synopsis of Program Methods
The program uses a separate method to represent each component of the runoff process that is illustrated in Figure 2, including:
- Methods that process precipitation, snow, and potential evapotranspiration meteorologic data.
- Methods that compute infiltration and the resulting runoff volume.
- Methods that represent direct runoff, including overland flow and interflow.
- Methods for describing baseflow.
- Methods for computing channel flow.
The methods that compute infiltration and the resulting runoff volume are listed in Table 3. These methods address questions about the volume of precipitation that falls on the watershed: How much infiltrates on pervious surfaces? How much runs off of the impervious surfaces? When does it run off?
The methods for surface runoff are listed in Table 4. These methods describe what happens as water that has not infiltrated or been stored on the watershed moves over or just beneath the watershed surface. Table 5 lists the models of baseflow. These simulate the slow subsurface drainage of water from the system into the channels.
The choices for modeling channel flow within the program are listed in Table 6. These so-called hydrologic routing models simulate one-dimensional open channel flow. An exception is the kinematic wave method which is a simplified hydraulic routing model.
Table 3.Loss methods for computing infiltration.
Model |
Categorization |
Deficit and constant |
continuous, spatially averaged, conceptual, measured parameter |
Exponential |
event, spatially averaged, empirical, fitted parameter |
Green and Ampt |
event, spatially averaged, conceptual, measured parameter |
Gridded deficit and constant |
continuous, distributed, conceptual, measured parameter |
Gridded SCS curve number |
event, distributed, empirical, fitted parameter |
Gridded SMA |
continuous, distributed, empirical, fitted parameter |
Initial and constant |
event, spatially averaged, conceptual, fitted and measured parameter |
SCS curve number |
event, spatially averaged, empirical, fitted parameter |
Smith Parlange |
event, spatially averaged, conceptual, measured parameter |
Soil moisture accounting (SMA) |
continuous, spatially averaged, conceptual, fitted and measured parameter |
Table 4. Transform methods for computing surface runoff.
Model |
Categorization |
User-specified unit hydrograph (UH) |
event, spatially averaged, empirical, fitted parameter |
User-specified s-graph |
event, spatially averaged, empirical, fitted parameter |
Clark's UH |
event, spatially averaged, empirical, fitted parameter |
Snyder's UH |
event, spatially averaged, empirical, fitted and measured parameter |
SCS UH |
event, spatially averaged, empirical, fitted parameter |
ModClark |
event, distributed, empirical, fitted parameter |
Kinematic wave |
continuous, spatially averaged, conceptual, measured parameter |
Table 5.Baseflow methods for computing subsurface flow.
Model |
Categorization |
Bounded recession |
event, spatially averaged, empirical, fitted parameter |
Constant monthly |
continuous, spatially averaged, empirical, fitted parameter |
Exponential recession |
event, spatially averaged, empirical, fitted parameter |
Linear reservoir |
continuous, spatially averaged, empirical, fitted parameter |
Nonlinear Boussinesq |
event, spatially averaged, conceptual, measured parameter |
Table 6.Routing methods for computing open channel flow..
Model |
Categorization |
Kinematic wave |
continuous, spatially averaged, conceptual, measured parameter |
Lag |
continuous, spatially averaged, empirical, fitted parameter |
Modified Puls |
continuous, spatially averaged, empirical, fitted parameter |
Muskingum |
event, spatially averaged, empirical, fitted parameter |
Muskingum-Cunge |
continuous, spatially averaged, quasi-conceptual, measured parameter |
Straddle-stagger |
continuous, spatially averaged, empirical, fitted parameter |
Confluence |
continuous, conceptual, measured parameter |
Bifurcation |
continuous, conceptual, measured parameter |
Reservoir |
Continuous, empirical or conceptual, measured parameter |