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<br />includes the stepped discharge and the longer duration, higher discharge of the snowmelt <br /> <br />runoff peak of spring 1997, for a total duration of six months. <br /> <br /> <br />As a management test ofHEC-6, an initial computer simulation was completed <br /> <br /> <br />using minimal field data, and selecting default values for input variables where provided <br /> <br /> <br />by the model. This situation represents many water resource management applications of <br /> <br /> <br />HEC-6 where field data are generally not available but the questions regarding sediment <br /> <br /> <br />movement out of the system of interest can only be answered by the use of a computer <br /> <br />model. Sequentially more field data were added to the simulations to determine the <br /> <br /> <br />sensitivity of the model to the availability of input data, Ultimately, the full suite of field <br /> <br /> <br />data was incorporated into model simulations for the most robust simulations. Input <br /> <br /> <br />variables for both models are detined in Table 2. <br /> <br />Sensitivity Analyses <br /> <br /> <br />Numerous sensitivity analyses were conducted on the input parameters for which <br /> <br /> <br />there was uncertainty, The objective of the sensitivity analysis is to determine the effect <br /> <br /> <br />of varied input on the model output in order to characterize error. Relative roughness, or <br /> <br /> <br />'n' value. moveable bed limils, iterations of the Exner equation, sediment transport <br /> <br /> <br />equation, and time step were evaluated for sensitivity on the model results (Table 2), <br /> <br /> <br />Only those settings that converged on the most accurate results are presented here. <br /> <br />Results <br /> <br /> <br />The stepped, experimental release 01'3.4 ml/s scoured many pools below lhe dam <br /> <br /> <br />to bedrock along the central thalweg. while simultaneously depositing sediments in larger <br /> <br /> <br />and higher bars along the channel margins (Figure 4), Pools near the dam were gradually <br /> <br /> <br />depleted of sediment, and sediment moved as a wave to adjacent downstream pools. <br /> <br /> <br />After the snowmelt peak, which was an unusually high and sustained melt for the North <br /> <br /> <br />Fork (Figure 2), both of the pools in the study reach were scoured to bedrock, and <br /> <br /> <br />substantially widened (Figure 4), These quantifiable changes in channel cross sectional <br /> <br /> <br />geometry provided information that was used to calibrate and compare the modeling <br /> <br /> <br />results, <br /> <br />9 <br />