How to setup a coastal flooding simulation 

This article will cover the necessary steps to run a coastal flooding simulation in OpenFlows FLOOD. 

Problem

OpenFlows FLOOD can address coastal flooding due to storm surge in two ways: (1) explicitly simulating the storm surge generation (with a regional scale coastal hydrodynamic model coupled with a regional scale meteorological model, providing winds and atmospheric pressure to the hydrodynamic model) or (2) implicitly simulating the storm surge sea level elevations as a boundary condition for a high resolution model of the flooded coastal area. This article covers the simpler latter method. In order to do it, a pre-requisite is to have a storm surge water elevations time series. This data can be obtained obtained from local tide gauge observations or from other models. Additionally, keep in mind that the method presented here only applied for limited areas, as water elevations can greatly vary in space (and time) in regional scale, so the validity of this approach is limited to relatively small scale applications (few kms of coastline at most) 

OpenFlows FLOOD's coastal flooding simulations will quantify the temporal and spatial variability of water elevations and flow in the a certain coastal area. It computes how much and when, each area of your region of interest is affected, taking into account that water is flowing, finding obstacles, deviating from buildings, infiltrating and flowing in/out of storm water drainage systems.

Solution

As the principle behind this type of simulation is that the area of interest for the simulation is limited (small scale) and the objective is to model how the coastal area is inundated and not so much simulate the coastal hydrodynamics, we can use MOHID Land’s engine to compute the simulation.

To create a new workspace and model simulation, follow the steps presented in this article. 

To create a time series file with the sea level data you can follow the instructions described here for rainfall. Simple follow the same steps but using the sea level data. Save the file in the folder “\General Data\Boundary Conditions\StormSurge.dat".

In order to simulate the coastal flooding, a variable sea level elevation will be imposed as a boundary condition at the open boundary. FLOOD’s current version 10.03 does not allow for a full configuration of the coastal flooding setup via the graphical user interface, so you’ll need to enable the model configuration to be made via the text editor. Follow the instructions shown in this article to do that.

The open boundary in FLOOD’s MOHID Land engine is defined based on the terrain elevations defined in the gridded digital terrain model file (Grid Data format). FLOOD will consider that the open boundary will be the points below a certain elevation (defined by a keyword called MAX_DTM_FOR_BOUNDARY) that lie at the edge of the computational grid or adjacent to a “non-compute” point. If necessary, the Edit Grid Data tool can be used to set the values of the model domain open boundary to a specific value X and set the MAX_DTM_FOR_BOUNDARY to a value Y just above it. This means that all grid points with elevation lower than Y that are near the model domain edges or adjacent to a “non-compute” point, will be considered open boundary, and the sea level data from the storm surge will be imposed there. 

In the module RunOff, apart from the standard configuration options, you’ll need to activate the following options:  

IMPOSE_BOUNDARY_VALUE  : 1 

ALLOW_BOUNDARY_INFLOW : 1

MAX_DTM_FOR_BOUNDARY  : -4

<begin_boundary>
FILE_IN_TIME                           : TIMESERIE
DEFAULTVALUE                      : 0.0
FILENAME                                  : ..\General Data\Boundary Conditions\StormSurge.dat
DATA_COLUMN                        : 2
<end_boundary>

Having setup this, you can run the simulation, visualize the results with the water level rising through the open boundary and flooding the coastal area.

See Also