Information on Other Objects When Reservoirs Are Disabled
Because the USACE‑SWD methods are a system approach, disabling reservoirs can affect other objects, processes, or operating policies. The following sections identify some issues to keep in mind when using this functionality.
Diversions Based on Disabled Reservoirs
No diversions are ever made from a disabled reservoir. Reach diversions will continue to be made based on their diversion requests.
On the Water User, and Diversion Object, there are methods called Reservoir Level Lookup which compute the Diversion Requested based on the level of a single reference reservoir. If that reference reservoir is disabled, the request slots are set to zero and a brown warning message is issued (one per run). If you wish to use an alternative diversion request, add an action to the script to change the method. When you want to undo the unregulated conditions, that script could reset the method back to the original method and it would be regulated again. No manual changes would be necessary.
To turn off reach diversions or to use an alternative value, select a different request method on the water user or diversion object within the script that unregulates the system. The most likely choice would be the Periodic Diversion Request method which allows you to specify a periodic slot of diversion requests. A single value in the table would represent a scalar request. To undo this action, use the Set Method action to reselect the original method. The original table data will then be used. Alternatively, set the Diversion to a specified value. Use the Set Series Slot Values action to set the Diversion equal to a set of values for all timesteps in the run. To undo this action, add a Set Series Slot Flags action that changes all those slots zero diversion slots to have the O flag. On the next run, the values will be cleared and the values will be recomputed. This approach would be useful if you have diversions that are not periodic or scalar.
In addition, in the Reservoir Diversions policy, you can divert water from one reservoir to another reservoir; see Reservoir Diversions for details. That Demand reservoir can limit the diversion from the supply reservoir. If the Demand reservoir is disabled and set to Pass Inflows, it will issue an error that it does not have an operating level. You should change the method on water user to not limit by reservoir level.
Seepage Methods
In some models, Seepage is set to an input and linked to the downstream object. If this was used this way in an unregulated model, it would add water to the system. Instead, a seepage method like Single Seepage Value should be selected on the disabled reservoir. Then no Seepage will be set.
Hydropower Releases Downstream Search
The hydropower release algorithm proposes a hydropower release and then searches downstream to see if it causes additional downstream flooding. This algorithm is designed to stop at a downstream reservoir. But, if the downstream reservoir is disabled and is set to Pass Inflows, the search continues downstream as though the reservoir was not there. See Hydropower for details on the algorithm.
Low-flow Requirements Based on Disabled Reservoirs
On the Control Point, there is a method called Reservoir Level Lookup which computes the low-flow requirement based on the level of a single reference reservoir. If that reference reservoir is disabled, the following behavior now occurs:
• Simulation (fully unregulated). No Low-flow Requirement is computed, but the run can continue. This assumes no operations are made to meet these demands.
• Rulebased Simulation (partially unregulated). An error is issued as the low-flow computation is not valid. A different Low-flow Requirement method should be selected.
Revised: 07/09/2023