PART VII: SUMMARY AND CONCLUSION 



182. This report introduces a numerical model called DYNLETl , developed 

 for project- level reconnaissance studies of inlet hydrodynamics. The model 

 simulates tidal flow based on an implicit finite-difference representation of 

 the one -dimensional shallow-water equations. It computes water surface eleva- 

 tions and average velocities as a function of time in tidal inlets ranging in 

 configuration from single channels connecting a bay to the sea to complex 

 inlet systems consisting of interconnected channels with and without bays. 



183. The numerical scheme replaces partial derivatives in the complete 

 governing momentum and continuity equations by finite differences, leading to 

 a system of nonlinear algebraic equations solved by iteration. By taking 

 advantage of handedness of the equation systems, an efficient computation 

 scheme can be employed. The numerical solution procedure is unconditionally 

 stable, and large time steps consistent with the resolution of the input data 

 can be used. 



184. General types of boundary conditions are easily implemented and 

 include the velocity, discharge, and water surface elevation. The model has 

 great flexibility in data input; data can be input in free format, cross - 

 sectional properties can be entered with varying distance intervals, and time- 

 dependent boundary data can be entered with variable time intervals. The data 

 can be submitted through batch files, or the model can generate an input file 

 using an interactive screen entry system under development and not described 

 here. Other features of use to the practicing engineer are the generation of 

 graphs of various types for display on the monitor or for obtaining hard copy. 



185. Application of the model was illustrated through two case studies. 

 One study site was Masonboro Inlet, North Carolina, for which an extensive set 

 of field data for model testing is available. DYNLETl successfully reproduced 

 the magnitudes and phases of average velocities and volume flow rates for this 

 situation involving five channels and no bay. 



186. The other study site was Indian River Inlet, Delaware, for which a 

 set of extensive field data for model testing is also available. The numeri- 

 cal model successfully reproduced the magnitudes and phases of average veloci- 

 ties and water surface elevations for the inlet system consisting of two large 

 bays and a narrow inlet throat perturbed by bridge pilings. This example also 



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