Unlike most User Method Categories, the Link Structure category, is selected from the menu bar at the top of the Open Object dialog for the Agg Diversion Site.

As described previously, there are three User Methods in the Link Structure category, which define how the Water User objects behave relative to each other and their containing Agg Diversion Site object.

Following is a description of each user method or structure and the associated slots and engineering calculations.

The No Structure method is commonly referred to as the standalone or default structure. This method treats the Agg Diversion Site object as a container for separate, standalone, Water Users.

Each Water User is linked by the user directly to the reach or reservoir from which it is diverting water. However, each reach or reservoir Diversion slot or Available for Diversion slot should have only one link; that is, a reach or reservoir can be linked to one and only one Water User for the No Structure method. This approach is good for highly diverted, highly regulated rivers where each diversion and return must be tracked in the river reaches. Figure 3.1 shows the linking structure.

Because the Water Users are directly linked to a reach or reservoir, the Agg Diversion Site never dispatches. Therefore, there are no input slots.

The Sequential Structure models a group of Water Users based on an order of allocation—perhaps by senior water right, for example.

The Agg Diversion Site diverts a bulk amount of water, from a reach or reservoir, and passes it to the first Water User, who takes its requested amount, if possible, and passes the remaining water on to the next user. In this way, the junior users may get only part or none of their requested amount. Excess is returned to the Agg Diversion Site, via the Total Unused Water slot. Each water user processes its delivered amount, and all return flows are handled on a per-Water User basis; that is, each Water User links its returns back to the river individually.

Optionally, you can create a link between Return Flow and the reach or reservoir. If no link is specified, the Return Flow is included in the Incoming Available Water for the next Water User. The Outgoing Available Water from the last Water User, including Return Flow if it is not linked, is linked to the Total Unused Water slot.

The Lumped Structure models a group of Water User’s requests as a single lumped sum. The individual requests are summed in the Total Diversion Requested slot on the Agg Diversion Site, and a comparison is made with the Total Available for Diversion slot. If the total request can be met, the Diversion slot is set to that amount; if not, the Diversion slot is set to the Total Available for Diversion amount.

In this scheme, the Return Flow is also lumped. The Total Depletion Requested slot tracks the sum of the individual Water User’s consumption requests. If a total deficit occurs in the Diversion, the Return Flows are recalculated based on the ratio of the Total Depletion Requested to the Total Diversion Requested. The Total Depletion Shortage is computed as the difference between Total Depletion Request and Depletion. The Total Depletion Shortage is then used to allocate the shortage to the member elements proportional to their depletion request.

It is not necessary to use Water User elements with this linking structure. If desired, Total Diversion Requested and Total Depletion Requested can be input directly by the user. However, it is often desirable to use one or more Water User objects for this purpose.