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Reach Objects
The Reach object is used to route water through the network. Also, water diversions from the river must come out of the Reach object. The Inflow slot should be linked upstream and the Outflow slot should be linked downstream. See User Methods in Objects and Methods for details about user methods not discussed here.
The Step Response routing method is typically used by the USACE‑SWD; see Step Response in Objects and Methods for details. This is the same routing algorithm used in the FloodControl predefined function in RiverWare. If the user selects a different routing method, then the final releases will be routed with a different method than that used in the algorithm to determine the flood control releases.
If the Step Response method is selected, input the number of routing coefficients in the Num of Coeff slot on the reach object. The routing coefficients are input in the Lag Coeff slot. These coefficients are the INCREMENTAL routing coefficients that apply to that reach specifically (as opposed to the direct routing coefficients used on the control points for the computation of flood control releases).
Sometimes, the routing coefficients are not fixed, but are dependent on the flow in the reach, particularly during high flow events. In this situation, the Variable Step Response routing method should be used; see Variable Step Response in Objects and Methods for details. See Alternative Routing Coefficients Methods for details.
Solve Downstream Only
On any reach in the model that does not have routing (i.e. the No Routing method is selected), the user should select the No Local Inflow, Solve Outflow method in the Local Inflow and Solution Direction category; see No Local Inflow, Solve Outflow in Objects and Methods for details. This method forces the reach to always solve in the downstream direction. This eliminates the possibility of unintentional upstream solving as a result of complicated rule priorities.
Transit Losses
In certain basins, the USACE‑SWD simulates the loss of water released from a reservoir to meet downstream demands. In the GainLoss category, the Base Plus Fractional Loss method models loss to meet all the following criteria. See Base Plus Fractional Loss in Objects and Methods for details.
• Base loss
• Loss that is a fraction of flow above that base loss
• Total loss cannot exceed a maximum flow rate
In addition, the base loss and fraction above that base can be entered seasonally for future extensibility. Select this method or another method in this category to model transit losses.
Revised: 01/05/2024