Continuous:Continuous Simulations

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GSSHA can be used to perform continuous simulations by specifying the LONG_TERM card in the project file, and providing the necessary input data. Continuous simulations require that one of two optional methods for calculating evapo-transpiration (ET) be selected, Deardorff (1978) or Penman-Monteith (Monteith, 1965, 1981), as described in Section 9.1. Hourly hydrometeorological observations are required for either method. The file containing the hourly values of hydrometeorological values is specified with the HMET_TYPE card. The TYPE can be WES, SAMPSON, or SURFAWAYS, as described in Section 9.3. The hydrometeorological inputs are used to compute potential evapo-transpiration (PET) with one of two ET methods. This PET is then sent to the chosen soil moisture accounting method as a demand. The amount of the demand that can be satisfied is the actual ET (AET). The AET is met based on the soil hydraulic properties, soil mositure, balance with other sources (infiltration, flow from groundwater) and demands (drainage). Anytime long-term simulations are performed snowfall accumulation and melting are also calculated, Section 9.2. To perform long term simulations, infiltration must be calculated with either GAR or RE by use of the INF_REDIST or INF_RICHARDS cards, respectively. In GSSHA v5 and above the multi-layer GA model can also be used for continuous simulations. Multi-layer GA is specified with the INF_LAYERED_SOIL card. When the GAR or multi-layer GA method of infiltration is specified, soil moistures are calculated with a two layer soil moisture model, as described in section 9.2. When RE is chosen, soil moisture is calculated as part of the overall solution.

GSSHA User's Manual

9 Continuous
9.1     Computation of Evaporation and Evapo-transpiration
9.2     Computation of Soil Moisture
9.3     Hydrometeorological Data
9.4     Snowfall Accumulation and Melting
9.5     Sequence of Events During Long-Term Simulations