Simulation of Estuarine Flooding and Dewatering with a
Fixed-Boundary Finite-Element Grid
Bathymetric Depth of Great Bay, New Hampshire
Abstract
A finite element model for simulating tidal flooding and dewatering
of shallow estuaries is described and applications to hypothetical
embayments and to the Great Bay, New Hampshire estuary system are
presented. The model incorporate two-dimensional kinematic wave physics,
with a porous medium beneath the open channel to incorporate realistic
drainage of dry elements on a fixed, high resolution mesh.
The Galerkin method is used on simple linear finite elements and
solved implicitly with iteration in time.
Simulations of idealized channels conserve mass, display physically
correct behavior, and agree with applicable one-dimensional results.
Solutions for the Great Bay estuary system further illustrate the
physics of tidal flat hydrodynamics, characteristic distributions of
bottom shear stress, and the influence of topography on the overall
circulation in the region. Sediment transport implications are discussed.
Summary
We have described and implemented a fixed grid finite element equation
based on the two-dimensional kinematic diffusion model with nonlinear
diffusion coefficient. A porous medium representation accounts for
tidal flat drainage as the depth approaches small values comparable
to the local sub-grid roughness. The model realistically
simulates tidal flow allowing flooding and dewatering during flood
and ebb stages. The two-dimensional model successfully reproduces
identical results of a one-dimensional flooding and dewatering of a
straight channel with uniformly sloping bathymetry. It also simulates
rectangular channels with linearly sloping bottom and with an V-shaped
and an asymmetric W-shaped depth profiles. The numerical solutions
are smooth and physically consistent, and without any noticeable
oscillation and distress in all the residual and transient analyses.
Water is conserved throughout simulations.
Application to the Great Bay estuary system shows very promising
results. Based on the lunar tide (M2) forcing, the residual
bottom stress is most intensified within the deep channel within the
5m isobath, and the residual sediment transport is concentrated at
the narrow strait connecting the northern channel and the lower bay.
[ Flooding/dewatering ]
[ Introduction ]
[ Kinematic model ]
[ Benchmarks ]
[ Great Bay ]
[ References ]
justin.ip@Dartmouth.EDU
Last modified: October 25, 1997 (JTI)
Introduction
Kinematic-Diffusion Model
Benchmark Studies
Great Bay,
New Hampshire
References