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which compute the rainfall-runoff and soil erosion in upland fields and the flow routing
and sediment transport in channels, respectively. This splitting has practical merits.
However, because channel and watershed are deeply interrelated, watershed and chan-
nel simulations should be integrated for a successful watershed-scale study. The two
parts in the integrated modeling system can complement each other to produce a bet-
ter prediction. Watershed simulation provides a good description of upland runoff
and soil erosion, especially for those ungauged watersheds, while channel simulation
enhances the watershed-scale study by providing more accurate flow routing, sediment
transport, and morphological evolution in channels.
8.3.1 Modeling components
A watershed model can be integrated with a 1-D, 2-D, or 3-D channel model in various
ways. Here, the integration between the channel network model CCHE1D and the
watershed model AGNPS or SWAT, as shown in Fig. 8.12, is used as an example to
illustrate the concepts andmethodologies of integration, which can be readily extended
to other models. This integrated watershed-channel modeling system includes three
model components: landscape analysis, watershed simulation, and channel simulation
(Vieira and Wu, 2002), as described below.
Figure 8.12
Integration of channel and watershed models.
Landscape analysis
The landscape analysis tool used here is the Topographic PArameteriZation (TOPAZ)
program (Garbrecht and Martz, 1995), which comprehensively analyzes the raster
Digital Elevation Models (DEM) to segment watersheds, define drainage divides,
identify drainage networks, and parameterize subwatersheds.
