Building a Model:Channel Routing

While small watersheds with no well defined channel may be simulated without channel routing, large basins or basins with a defined channel almost always need channel routing to accurately reproduce the outlet flow. There are many possible ways to locate the stream. The location of the stream network may be surveyed, come from USGS .dlg files or other sources of digital stream network, or the stream delineation provided by TOPAZ may be used. In any case, as with the overland flow, it is best to start with a simple channel network and add complexity. As a first approximation, the main stem and only major tributaries should be included in the stream network. Once the simple network is running, additional stream segments can be added. As the stream segments begin to represent smaller and smaller tributaries, the effect of adding additional streams will begin to diminish.

As discussed in Section 5.1, ideally the steam network comes with surveyed cross-sections and thalweg elevations. Also discussed in Section 5.1.5 is a procedure for taking stream bottom elevations from the DEM. As discussed in this section, it will be important to smooth the thalweg elevations to create a realistic channel profile and perhaps edit the grid elevations to ensure that overland flow can enter the stream. Whether to use break-point cross-sections or trapezoidal approximations generally depends on the availability of surveyed cross-sections.