DYNLETl: DYNAMIC IMPLICIT NUMERICAL MODEL OF 

 ONE -DIMENSIONAL TIDAL FLOW THROUGH INLETS 



PART I: INTRODUCTION 



Background and Motivation 



1. The US Army Corps of Engineers (USACE) has responsibility for 

 creating and maintaining navigable US waterways. Tidal Inlets that connect 

 the ocean with bays, estuaries, and sounds constitute a major component of 

 this navigation system. The design and construction of navigation improve- 

 ments to existing inlets is an Important part of the USACE responsibility, and 

 each year the USACE dredges millions of cubic yards of sediments from tidal 

 inlets to maintain navigability. 



2. To a great extent, the sand- trapping capacity of inlets determines 

 the long-term evolution of the shoreline position on adjacent beaches. The 

 sand-trapping capacity depends on such factors as the strength of the tidal 

 flow, morphology of the shoals at the inlet, wave action, and condition and 

 configuration of the navigation channel and inlet structures, such as jetties. 



3. The channel shoaling rate, inlet shoal morphology, and inlet bank 

 position are to a great extent controlled by the tidal flow through an inlet. 

 Accurate and efficient calculation of the hydraulic characteristics of Inlets 

 is, therefore, Important for project planning and engineering involving 

 navigation, inlet stability, beach and side bank evolution, and the flushing 

 of bays and lagoons. Quantitative understanding of tidal flow at inlets is, 

 of course, also required to achieve understanding of fundamental hydrodynamlc 

 and morphodynamic processes at inlets. 



4. In the past two decades, sophisticated two- and three-dimensional 

 numerical simulation models have been developed for computing detailed 

 processes of inlet hydrodynamics (Butler 1980, 1982; Johnson et al . 1989; 

 Clalone, in preparation) and water-quality aspects (Kim, Johnson, and Sheng 

 1989) of Inlets. Special expertise and a powerful mainframe computer are 

 required to set up and run these types of models, however, and they are not, 

 as yet, available to the non-modeling coastal or dredging planner, engineer, 

 and geophysical researcher. 



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