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Soil Moisture Accounting

The State Model has the ability to include soil moisture as a water supply. See Section 7.3 for additional discussion on how to implement soil moisture accounting. The soil moisture capacity is calculated as follows:

where:

\(SM\) = Soil Moisture;

\(D\) = Soil Depth: average soil depth provided for all structures in the control (*.ctl) file;

\(A\) = Area: data provided by structure in the annual time series (*.ipy) file;

\(C\) = Soil Moisture Capacity: data provided by structure in the soil parameter (*.par) file or in the consumptive use structure (*.str) file

  • The Soil Moisture option allows water to be stored in the soil zone up to its capacity and the diverting structures (direct diversion or well) efficiency.
  • StateMod initializes the soil moisture reservoir contents to be 50% of the soil moisture capacity.
  • If the irrigated area of a structure is reduced from one year to the next and the resulting soil moisture capacity is exceeded any water in excess of the capacity is estimated to be a loss attributed to that structure.
  • The Soil Moisture option requires the variable efficiency option (see Section 3.5) be used.
  • In a simulation mode, the Soil Moisture option uses an operating rule to specify an administration date that controls when water is available to be taken out of the soil zone to satisfy a consumptive (not total) demand. In order to represent water use when historic diversions are provided as a demand this operating rule allows water to be taken out of the soil zone when a structure's consumptive irrigation water requirement exists even if the user has specified the structures demand to be zero.
  • In the baseflow mode, the Soil Moisture option takes water out of the soil zone to satisfy a consumptive (not total) demand after surface water and well water use occurs. In order to represent water use in baseflow mode, water can be taken out of the soil zone when a structure's consumptive irrigation water requirement exists even if the user has specified the structures diversion and pumping to be zero.