A runoff model
simulates the rainfall - runoff
response of a rainfall catchment area. It produces a time series of runoff rates based on input meteorological time series.
Modeling Runoff in GoldSim
Runoff models vary in complexity. The simplest runoff model in GoldSim is a unit hydrograph convolution. There are two examples of this in the model library: unit hydrograph convolution using lookup table
and triangular unit hydrograph convolution
. In the first example, a hydrograph response is specified in the form of a lookup table. The lookup table has lag times as its independent variable, and the dependent variable is the fraction of the rain input that is discharged after a given lag time. Convolving this with a time series of precipitation produces a lagged time series of runoff. This is a simple calculation in GoldSim with 3 or 4 elements and it can reproduce observed runoff responses well in some cases. The second example (triangular unit hydrograph convolution
) is similarly simple but uses a functional represenation of a triangular unit hydrograph instead of a lookup table.
In other cases, there are not enough data to build empirical models like unit hydrograph convolutions and it is necessary to resort to a more complex deterministic model. These models simulate infiltration and storages of water in catchments as reservoirs with time varying inflow and outflow rates.
Thus far, the deterministic runoff models that have been developed in GoldSim include the Australian Water Balance Model (AWBM)
and the water balance module of the Hydrologic Simulation Program Fortran (HSPF)
. Of these two models, AWBM has simpler calculations and requires fewer input parameters. It is well suited for mine water balance models and other water balance models running on daily or hourly time steps.
The HSPF water balance model, as implemented in GoldSim, has more input parameters to allow for more specialized runoff modeling applications. For example, there is a parameter specifically to model baseflow withdrawal by phreatophytic vegetation, i.e. vegetation that draws its water from groundwater baseflow rather than soil water and precipitation. HSPF is typically run on a time step of one hour or shorter and is well suited to modeling applications where the subdaily runoff timing is important, as in stormwater engineering for example.
Once you model runoff using HSPF, AWBM, or convolution elements, you may be interested in routing flows using Muskingum channel routing
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