Figure 7-41 shows an inflow hydrograph (dashed green line) and two outflow hydrographs (solid blue and black line with squares). An example of varying cross section spacing is shown in Figure 7-41.
Also, if the distance between cross sections is so great, such that the Courant number would be much smaller than 1.0, then the model may also become unstable. In general, cross sections spaced too far apart will cause additional numerical diffusion, due to the derivatives with respect to distance being averaged over to long of a distance. Not enough cross sections: When cross sections are spaced far apart, and the changes in hydraulic properties are great, the solution can become unstable. However, most streams lie some where in between these two spacing distances. Larger uniform rivers with flat slopes may only require cross sections on the order of 5000 ft or more. Streams flowing at high velocities may require cross sections on the order of 100 feet or less. Steeper slopes require more cross sections. Cross sections must also be added at levees, bridges, culverts, and other structures.īed slope plays an important role in cross section spacing. Additional cross sections should be added at locations where changes occur in discharge, slope, velocity, and roughness. Cross sections should be placed at representative locations to describe the changes in geometry.