【正文】 lows occurring only in the lower reaches of the watershed. The runoff produced by storm events swiftly exits the watershed, and the discharge returns to base flow levels within one to three days. The sediments are transported in the channels as bed load and suspended load, and range from silt () to sand to gravel (65mm). Fourteen fullyinstrumented flumes were constructed in the channels to control degradation of the channel bed and to monitor runoff and sediment yield. Figure 5 shows the channel network of Goodwin Creek extracted from a Digital Elevation Model using TOPAZ. Ten instream measuring flumes and four culverts, located in the channels of Strahler order two or higher, are considered. The simulation duration is 18 years, from January 1978 to December 1995, with a total of 1192 storm events. The time step used in the calculation is 15 minutes. The runoff and sediment yield from the upland fields generated with SWAT (Bingner et al., 1997) are used as the inflow conditions for the simulation of flow and sediment transport in the channel network. The model calibration done by Wu, Vieira and Wang (2000) showed that the CCHE1D model provided good predictions of the channel evolution and sediment yield in this watershed. Here, the sensitivity analysis of this model to the nonequilibrium adaptation length and the mixing layer thickness is conducted. Figure 5. Channel Network with Hydraulic Structures in Goodwin Creek At first, the nonequilibrium adaptation coefficient α, which is used to calculate the nonequilibrium adaptation length for suspended load, is given values of , , and , while other parameters are kept invariable. Here, the sediment transport capacity is calculated by Wu, Wang and Jia’s (2000) formula. Figure 6 shows the parison of the calculated silt, sand and gravel yields using various α. Table 1 provides the quantitative information about this parison. As α increases from to , the gravel yield increases 27%, and the silt yield decreases 9%。 N is the total number of size classes。 ? Abk / ? t is the bed deformation rate of size class k. The bed material is divided into several layers. The variation of bed material gradation pbk at the mixing layer (surface layer) is determined by the following equation (Wu and Li, 1992) (4)where Am is the crosssectional area of the mixing layer。 and qlk is the side sediment discharge from banks or tributaries per unit channel length, with the contribution from banks being simulated by CCHE1D bank erosion and bank failure module, and the contribution from upland erosion being simulated by SWAT or AGNPS. The sediment transport capacity can be written as a general form (2)where pbk is the bed material gradation。 Qt*k is the totalload transport capacity。 Ctk is the depthaveraged totalload concentration of size class k。 FAX (662) 9157796。附 錄附錄一：外文原文Sensitivity Analysis of the CCHE1D Channel Network Model Weiming Wu (1), Dalmo A. Vieira (2), Abdul Khan (3) and Sam S. Y. Wang (4) (1), (2), (3) and (4), National Center for Computational Hydroscience and Engineering, School of Engineering, The University of Mississippi, MS 38677。 PH (662) 9155673 / (662) 9157788。 Email: wuwm AbstractThe CCHE1D model was designed to simulate longterm flow and sediment transport in channel networks to support the DEC project. It uses either the dynamic wave or the diffusive wave model to pute unsteady flows in channel networks with pound cross sections, taking into account the effects of instream hydraulic structures, such as culverts, weirs, drop structures, and bridge crossings. It simulates nonuniform sediment transport using a nonequilibrium approach, and calculates bank toe erosion and mass failure due to channel incision. The CCHE1D model decouples the flow and sediment transport calculations but couples the calculations of nonuniform sediment transport, bed changes and bed material sorting in order to enhance the numerical stability of the model. In this paper, the sensitivity of CCHE1D to parameters such as the nonequilibrium adaptation length of sediment transport and the mixing layer thickness is evaluated in cases of channel aggradation and degradation in laboratory flumes as well as in a natural channel network. In the case of channel degradation, the simulated scour process is not sensitive to variation in values of the nonequilibrium adaptation length, but the determination of the mixing layer thickness is important to the putations of the equilibrium scour depth and of the bedmaterial size distribution at the armoring layer. The simulated bed profiles in the case of channel aggradation and the calculated sediment yield in the case of natural channel network are insensitive to the prescription of both the nonequilibrium adaptation length and the mixing layer thickness. The CCHE1D model can provide reliable results even when these two parameters are given a wide range of values. Introduction The CCHE1D model was designed to simulate longterm flow and sediment transport in channel networks to support the Demonstration Erosion Control (DEC) project, which is an interagency cooperative effort among the US Army Corps of Engineers (COE), the Natural Resources Conservation Service (NRCS) and the Agricultural Research Service (ARS) of the US Department of Agriculture. The CCHE1D version was based on the unsteady flow model DWAVNET (Diffusion WAVe model for channel NETworks, Langendeon, 1996) and the sediment transport model BEAMS (Bed and Bank Erosion Analysis Model for Streams, Li et al., 1996). It was significantly improved by implementing the dynamic wave model and the nonequilibrium sediment transport model (Wu, Vieira and Wang 2000). The CCHE1D was integrated with the landscape analysis tool TOPAZ (Garbrecht and Martz, 1995) and