Morphodynamic Equilibria in Tidal Embayments with Decreasing CrossSection

Morphodynamic Equilibria in Tidal Embayments with Decreasing Cross-Section Henk Schuttelaars The Institute for Marine and Atmospheric research Utrecht (IMAU) Utrecht University

Contents • • • Introduction Model Formulation Numerical Experiments Comparison with Observations Conclusions + Future Research

Introduction Tidal Embayments: • Semi-enclosed bodies of water • Connected to the open sea • Driven by tides Examples: • Frisian Inlet System • Western Scheldt • Inlets East Coast of the US

Marine Part of the Western Scheldt

Research Questions • Do Long-Term Equilibria Exist • Are They Unique and Stable } PARAMETERS ?

Model Formulation • Idealized Models: Water Motion Sediment Transport Bed Evolution } Short Time Scale Long Time Scale Averaging

Model Equations and Assumptions • • • Depth Averaged Shallow Water Equations Only Bed Erodible Noncohesive Material Fine Sand Suspended Load Transport Sediment Balance: hole bar

Geometry Side View: Top View: WE Embayment X=0 WR X=L

Parameter Continuation Short Embayment: Analytical Solution • constantly sloping bed • spatially uniform hor and vert velocities • spatially uniform bed stress For other parameters, continue this known solution

The Experiments Experiment 1: • Reducing WR Different Types of Equilibria Experiment 2: • Comparison with data

Width Variation Bed Profile M 2 Phase Hor Vel 0 WR/WE -17 0 Depth in meters WR/WE -10 -27 Sea 110 km Land Sea WR/WE ~ 1 • Bed Weakly Concave • Travelling Wave • M 4 extern negligible 110 km WR/WE ~ 0. 5 • Bed Very Deep Decreasing WR • Standing Wave • M 4 extern amplified Land

Comparison With Field Data (1) Width-Averaged Depth

Comparison With Field Data (2) Sea Land

Conclusions Two Types of Equilibria: • externally driven • friction-related Idealized Model Reproduces Global Characteristics Quite Well Multiple Equilibria Maximum Embayment Length

Future Research • Closer Comparison With Process-Based Models and Observations • Introduce Two Dimensional Perturbations