Sometimes the computed floodway solution that

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: he study reach. Sometimes the computed floodway solution, that provides computed water surfaces at or near the target maximum, may be unreasonable when transferred to the map of the actual study reach. If this occurs, the user may need to change some of the encroachment stations, based on the visual inspection of the topo map. The floodway computations should be re-run with the new encroachment stations to ensure that the target maximum is not exceeded. 10-6 Chapter 10 Performing a Floodway Encroachment Analysis Viewing the Floodplain Encroachment Results Floodplain encroachment results can be viewed in both graphical and tabular modes. Graphically, the encroachment results show up on the cross section plots as well as the X-Y-Z Perspective plot. An example cross-section plot is shown in Figure 10.3. Figure 10.3 Example Cross Section Plot With Encroachments As shown in Figure 10.3, the encroachments are plotted as outlined blocks. In this example, the water surface profile for the base run (first profile) is plotted along with one of the encroached profiles. The user can plot as many profiles as they wish, but it may become a little confusing with several sets of encroachments plotted at they same time. Another type of graphic that can be used to view the encroachments is the XY-Z perspective plot, an example is shown in Figure 10.4. In this example, the base profile (profile 1) as well as one of the encroached profiles is plotted at the same time over a range of cross sections. This type of plot allows the user to get a reach view of the floodplain encroachment. The user can quickly see if the encroachments transition smoothly or if they are erratic. In general, the final encroachments should have a consistent and smooth 10-7 Chapter 10 Performing a Floodway Encroachment Analysis transition from one cross section to the next. With the assistance of this type of plot, the user may want to further refine the final encroachment stations and re-run the model. Figure 10.4 Example X-Y-Z Perspective Plot with Base and Encroached Profiles Encroachment results can also be viewed in a tabular mode from the Profile Output Tables. Select Profile Table from the View menu of the main HECRAS window. When the table comes up, the user can select from three different pre-defined encroachment tables. To bring up one of the encroachment tables, select Encroachment 1 from the Std. Tables menu on the Profile table window. An example of Encroachment 1 table is shown in Figure 10.5. The table shows the basic encroachment results of: computed water surface elevation; change in water surface from the base profile; the computed energy; top width of the active flow area; the flow in the left overbank, main channel, and right overbank; the left encroachment station; the station of the left bank of the main channel; the station of the right bank of the main channel; and the right encroachment station. 10-8 Chapter 10 Performing a Floodway Encroachment Analysis Figure 10.5 Example of the Encroachment 1 Standard Table Encroachment 2 table provides some additional information that is often used when plotting the encroachments onto...
View Full Document

This note was uploaded on 03/16/2013 for the course ENGINEERIN 401 taught by Professor Tommas during the Spring '13 term at University of Alberta.

Ask a homework question - tutors are online