reproduction of the salinity profiles in the Delaware River during a 

 period when the salinity front was advancing upstream is shown in Figure 

 3-33; an example of longer term salinity verification covering the period 

 when the salinity front advanced and retreated is shown in Figure 3-34. 



d. Hurricane Surges . Because of the infeasibility of reproducing 

 winds in an estuary model, prototype hurricane surge hydrographs must 



be adjusted to remove the effects of local winds. The model test results 

 reflect only the gravitational component of the surge and must be adjusted 

 to account for the local wind effects. The reproduction of normal tides 

 in conjunction with reproduction of hurricane surges is often suspended 

 because the contributions of normal tides to the total surge elevations 

 are often relatively small and can be easily added to the model results 

 by computer techniques. When separately adding the normal tide to the 

 model surge results, the phase of tide with respect to the surge and the 

 tidal range can be varied to determine the maximum and minimum effects of 

 the tide on the height of the peak surge. Removal of the tide factor 

 greatly simplifies the model operation procedure. If normal tides and 

 hurricane surges are generated concurrently, the tide generator is ad- 

 justed to reproduce the desired tide; then the surge generator is adjusted 

 to produce the observed water level history at the control gage. Because 

 the model roughness has previously been adjusted for normal tides and 

 currents, any adjustments to the roughness for accurate reproduction of 

 the hurricane surge are usually unnecessary. However, some modification 

 to the overbank rouglmess in areas subject to surge flooding may be nec- 

 essary. An example of hurricane-surge verification for a case where the 

 prototype data include normal tide and local wind effects is shown in 

 Figure 3-35. Figure 3-36 illustrates a case where local wind effects 

 have been removed from the prototype data. 



e. Shoaling . (Since this report was prepared, a hybrid modeling 

 technique has been developed for sedimentation studies. A physical 

 model is used to determine the hydrodynamic conditions which are then 

 used to drive a numerical sedimentation model.) The basic objective of 

 the fixed-bed model shoaling verification is to identify a synthetic sedi- 

 ment that will move and deposit under the influence of the model forces in 

 the same manner that the natural sediments move and deposit under the in- 

 fluence of the natural forces. Because no satisfactory similitude laws 

 have been developed for estuarine sedimentation, the development of the 

 modeling shoaling test procedure is more an art than a science at this 

 time. The appropriate time and volume scales for the shoaling tests must 

 be determined by trial and error. 



Many variables are involved in identifying a suitable operating tech- 

 nique for use in the model, and each must be resolved by trial and error 

 in the model. The most significant variables include: (a) Shape, size, 

 gradation, and specific gravity of the synthetic sediment; (b) method, 

 location, duration, and quantity of synthetic sediment injection; (c) rate 

 of freshwater inflow; (d) magnitude of tide; (e) height, direction, and 

 period of ocean waves; (f) length of model operation; and (g) readjustment 

 of model roughness. The model water temperature must be closely monitored. 



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