FMA Challenge 2

Introduction

If you haven't already completed FMA Challenge 1, please see this FMA Challenge 1 page. This page is for TUFLOW users of intermediate to advanced ability.

In this challenge, a tidally influenced floodplain and riverine system will be explored along the California Coast. More information is available in the "tidal-description.docx" in the ZIP compressed file provided.

From this challenge, it is expected the user will develop their skills in:

• Understanding tidal influences on floodplains and riverine systems,
• Influence of cell resolution on results and whether or not the model should contain a 1D component;
• Using a looped batch file to run through scenarios;
• Understanding comparisons between three different 2D solvers. These include TUFLOW classic, TUFLOW GPU and TUFLOW FV.
  
  

Data for this model is provided via ZIP compressed file posted on the internet/FTP for download.

Relevant Tutorials

It may be useful to revisit some of the following tutorials:

• General 2D modelling- Tutorial Module 1
• 2D topography modification- Tutorial Module 3

Information to Modelers

Assignment of all parameters for this analysis are at the discretion of the modeler. A high resolution aerial image is provided so that land cover details can be inspected. Information on the problem definition can be found on FMA_Challenge_Models/FMA_Scenario2/FMA_Challenge_Model_Introductions.

Relevant Files

It is up to the modeler's discretion to determine what GIS package to use, what text editor to use, and how to run their models (batch mode or within the text editor).All relevant files can be found on FMA_Challenge_Models/FMA_Scenario2/

Solution

A sample solution has been presented, courtesy of BMT WBM.

Cross section spacing, Grid Size, and Mesh Element Size

Fixed grid models of different resolutions and a flexible mesh model were set up. The fixed grid domains were orientated north-south.

The coarsest fixed grid and flexible mesh resolutions were sufficiently detailed to represent the river bathymetry, so no 1D/2D coupling was incorporated. A fully 2D solution is preferable over a 1D/2D linked representation provided the 2D resolution of the primary flowpaths is sufficiently fine. A minimum recommended 2D resolution across the river for TUFLOW for this model is a 30m grid (it is recommended that a minimum of 4 fixed grid cells be used for modeling a primary flowpath). For this model the upper sections near the two inflows are not represented well, especially the northern Tributary Inflow. However, this is unlikely to have an adverse effect on the objectives of the modeling, but would affect the comparison to the high water marks near these inflows.

As there is no 1D/2D linking, Challenge 2 provided an opportunity to provide some comparisons between our three different 2D solvers. Results from TUFLOW (finite difference implicit solution), TUFLOW’s GPU Module (explicit finite volume GPU solver over a grid), and TUFLOW FV (explicit finite volume flexible mesh) are presented.

The number of cross sections, grids, or mesh elements used were as follows:

2D Domain	Active 2D Cells/Elements
10m (grid)
15m (grid)
30m (grid)
FM (Flexible Mesh)*

• N.B. For the FM (Flexible Mesh) within the main flow channels the typical element width is 20 m and length 50 m (quadrilateral elements), and on the floodplains the typical size is 75 m to 100 m made up of quadrilaterals and triangles.