LISEM Classic

LISEM

Flooding

Flooding within hydrology

If you have followed the descriptions for modelling hydrology or groundwater, flooding is automatically set up. That is, if there is sufficient precipitation to cause flooding, the model will simulate this.

Simple water-flow simulation

To do a flood simulation without hydrology, little data and setup is required.

Elevation and Mannings N

First, get an elevation model and cut it to the desired extent. Second, define a Mannings N map. This paramter described surface roughness and determines friction for surface flows. This map can be made homogeneous (one single value for the entire model domain). If you wish to have a more detailed description, see the page about modelling hydrology.

Initial conditions

Besides terrain and surface roughness, you need to specify the initial water height, including river, lakes and other surface flows. We will use the following initial fluid height (in meters).

Modelling

There are two options to run this simulation. You can use the script environment to call the FlowDynamic function in a loop. This function provides highly accurate saint-venant surface flow with wave behavior. Such a script is provided below.



void main()
{

Map dem = dem.map;
Map whinitial = initialwaterheight.map;
Map n= dem * 0.0 + 0.1; //homogeneous mannings n of 0.1

Print("Create Initial Properties");

//a list with {height, x-velocity, y-velocity}
array<Map> flowprops = {whinitial,whinitial * 0.0,whinitial*0.0};

UILayer l = AddViewLayer( whinitial, "elevation",true);
for(int i = 0; i < 5000; i++)
{
flowprops = FlowDynamic(dem, n,flowprops[0],flowprops[1],flowprops[2],0.1);

ReplaceViewLayer(l, flowprops[0]);

//every 50 timesteps, store the flow height and velocity
if( i % 50== 0)
{
whelev.tif = dem+flowprops[0];
whvel.tif = sqrt(flowprops[2] *flowprops[2]  + flowprops[1] *flowprops[1]) ;

}
Print("Timestep : " + ToString(i));

}
}


The example data can be downloaded for: Elevation, Initial Water and Mannings N. The map view now shows the real-time results: