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Well Operational Considerations

  1. Wells may increase the water supply available at the river at a given time step if well return flows exceed the stream depletion. StateMod checks for such a condition and re-operates to allow senior ditches to benefit from the additional water supply.
  2. Wells may require two or more delay patterns to represent the delay associated with return flows and depletions. The data for both types of delays are specified in the unit response file (*.dly or *.urm). When the sum of return flows to the river is less than 100%, the balance is treated as a loss (e.g evaporation or phreatophytes). Similarly when the sum of depletions to the river is less than 100%, the balance is assumed to come from ground water storage.
  3. Wells may cause river flows to go negative when the well’s estimated depletion to the river exceeds the streamflow. StateMod treats such an occurrence as an indication that pumping impacts have depleted ground water storage rather than the stream flow. Under such a case, StateMod allows the pumping to occur and accounts for the source of water as originating from ground water storage. This water is presented in the column From/To GW Stor for each river node in the diversion summary output (*.xdd) and for the whole basin in the water budget report (*.xwb). Note the quantity of water supplied by ground water storage in a simulation time period is taken out of the stream the next time period before any water allocation occurs. The control file (*.ctl) variable iwell = 2 or 3 allows the repayment of this water to be limited to a maximum amount to represent a stream ground water system that are disconnected. Also, since data for this term is generally not observed, baseflow calculations may be influenced by this lack of data.
  4. Well information is presented in four columns of the diversion summary report (*.xdd). The column titled From Well describes the total amount of water pumped and made available to a diversion. The column titled Well Depletion represents the impact of a previous months pumping on the river. The column titled To/From GW Stor was described above. The column titled River by Well represents the impact of the current months pumping on the river. The Well Depletion and River by Well data are separated because the impact of a previous months pumping on the river influences the water supply available to all users before any diversions occur while the impact of the current months pumping impacts water rights that are junior to the well only. Note by definition, a well structure that is not tied to a diversion has no data under the column From Well. However, the columns titled Well Depletion and River by Well include the impact of all well pumping on the river.