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7 (4) Inflow hydrographs and downstream boundary conditi on (stage hydrograph if available) throughout the flood. 7. Model Limitations and Applicability: The use of HEC2SR is limited to a reach for which the one-dimensiona1- flow app roximat i on is app 1 i cab 1 e. The model accounts for neither 1 atera 1 channel migration nor secondary currents. The model assumes a uniform aggradation or degradation pattern along the reach, so that localized scour or deposition cannot be predicted. The model is not suitable for studying 10ng- term ri ver-bed changes, because of the hi gh cost of backwater computat i on using HEC-2. However, HEC2SR offers the option to input sediment inflows di rect1y or i nterna lly to generate sediment-1 oadi ng data by consi deri ng the sediment-transport capacities in the upstream main-channel and tributary reaches. The backwater results obtained using HEC-2 can be directly compared to stage predictions util ized in the conventional flood-insurance studies. The model also features modular structure, which enables users to modify each functional component. B. KUWASER (Known discharge. Uncoupled. WAter and SEdiment Routing): 1. Developer: Simons, Li, and Brown (Colorado State University), 1979 2. Previous Applications: (1) Yazoo River Basin (Simons, Li, and Brown, 1979) 3. Basic Concepts: The model was developed for simulating one-dimensional, spatially-varied, steady water and sediment flows. The principal assumptions it employs are as foll ows: (1) Hydraulic characteristics of flow remain constant for a specified time interval. (2) Hydrostatic pressure distribution prevails over any channel section. (3) Secondary flow is negligible. (4) Fri ct i on loss at a sect i on is the same as that for a uniform flow with the same velocity and hydraulic radius.