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<br />" <br /> <br />. <br /> <br />7. Calibrate the HEC-2 <br /> <br />. <br /> <br />HEC-2 is by far the most used and accepted computer program in floodplain <br />hydraulics today and will likely remain so for a long time in the future. <br />Therefore, it behooves us, as the "leading edge" of the profession, to utilize more <br />advanced techniques to analyze complex situations but then to translate the <br />solutions back into the standard HEC-2 routine. This can be achieved in most <br />situations; for example, if a bridge-modeling technique provides more accurate <br />elevations than the HEC-2 routines, adjustments to the HEC-2 profile can be <br />made by using varying effective flow areas, roughness or expansion contraction <br />coefficients, or, as a last resort, X-5. The modeler should, of course, provide the <br />alternative analysis by newer techniques as support for the calibration of the <br />HEC-2 model. This approach is analogous to that used when replicating a known <br />flood profile developed from high water marks and gage data. A second example <br />of this concept, one that is probably more frequently used, is the reexamination <br />of split-flow and break-out flow analyses. Two-dimensional modeling techniques <br />are being employed to more accurately estimate quantity and direction of flow <br />splits and the resultant water surface elevations. These solutions can, again, be <br />employed to calibrate the HEC-2 model rather than being substituted for it. <br />Similar examples could also be given regarding the application of moveable bed <br />models to alluvial systems. <br /> <br />This approach (use of more sophisticated models to calibrate HEC-2 models) <br />offers a very distinct advantage when applied to floodways and hydraulics <br />represented on NFlP maps. It does not attempt to substitute a very complex, <br />costly, and limited-use model for a well-respected standard model like HEC-2, <br />but rather, reinforces its use by further calibrating it. This, in turn, allows future <br />users of the data to rapidly understand the supporting documentation and to apply <br />less-sophisticated and less-costly techniques to evaluate minor changes to the <br />hydraulics. <br /> <br /> <br />In summary, this paper suggests approaches to support and shore up the HEC-2 model by <br />using more sophisticated models as calibration tools rather than as substitutes for the <br />standard. <br /> <br />. <br /> <br />5 <br /> <br />