The flow chart for multiple bridge design (Figure 9-19) illustrates the steps and considerations recommended in TxDOT designs.

When estimating the design high water at a multiple structure location, the design engineer still needs to determine how the flow divides itself across the floodplain at flood stage. In the case of multiple structures, the flow division indicates the approximate portion of the total flood discharge that will be carried by each structure. One method for estimating flow division is by actually observing the flow at design discharge and design high water at the proposed site. However, the ability to make such an observation when the proper set of circumstances occurs would be rare. Therefore, use the following analytical method to determine flow distribution and establish flow division.