Excercises

The hands-on exercises can be downloaded via subversion. Subversion is a well-known version management system that allows you to always have the most recent source code at hand. It also allows developers to commit changes to the source code, without interfering with other developers. In order to use Subversion, you will need a Subversion client. A well-known client for Windows is Tortoise. If you have registered, you can download the source code via the following URL: https://svn.oss.deltares.nl/repos/xbeach/Courses/DSD_2014/Examples – Basic. For the tools like Quickplot and Quickin the Delft3D environment is needed.

Dune erosion at Delfland, Netherlands (1D)

The first case we will run is a relative simple 1D case. It concerns a profile along the Dutch coast and the hydraulic boundary conditions are based on the 1953 storm surge that caused substantial flooding in the Netherlands.

You can work on the following assignments:

  1. Go to the folder “Examples\DelflandStorm” and double click the file “run_model.bat”. The simulation will start. The model will run for a few minutes, but in the meantime you can already work on question 2 to 5.
  2. Open params.txt in which you specify the model input files and settings. Check the number of grid-points in x-direction (keyword: nx) and y-direction (keyword: ny). Check the filenames in which you specify the wave conditions (keyword: bcfile) and the storm surge level (SSL) (keyword: zs0file).
  3. Do the wave conditions change during the simulation? What is/are the wave height(s) and wave period(s) applied in the simulation?
  4. Does the storm surge level change during the simulation? What is the maximum surge height in the simulation. Surge height is defined with respect to the mean sea level (MSL)?
  5. What is the simulation time (keyword: tstop)? Do we apply a morphological acceleration factor (keyword: morfac)? What variables are stored as output and with what time interval? How much hydrodynamic time is simulated?
  6. Probably the simulation has finished. When you start the model, it generates a file named XBlog.txt. Open this file and check what is stored in the file. What was the total simulation time?
  7. To check out the simulation results we make use of the Quickplot tool (A brief tutorial is attached to this document). You can start Quickplot via the Delft3D environment we installed (Start Programs Deltares Delft3D Delft3D). In the Delft 3D menu choose Utilities Quickplot. Choose Files of type “NetCDF files and GRIB files” and open “xboutput.nc” in the simulation folder.
  8. Use the Quickplot tutorial and try to make an animation in which you plot short wave height (H), water level (including long wave variations, zs) and bed level (zb) as function of time.
  9. Plot the offshore water level as function of time. Also open the file “tide.tek” (Tekal data files format), which contains the imposed surge level. Did the model correctly simulate the imposed surge level?
  10. Copy all model files to a new folder named “superfast”. Edit params.txt and set ny=0 (instead of ny=2), and run the model. What is the simulation time compare to the original simulation?
  11. Compare simulation results for the “superfast” and “default” simulation. Are these the same? What option will you use in the future?

Nourishment scenarios near Kijkduin, Holland (1D)

This case concerns the exploration of a nourishment strategy near Kijkduin along the Holland coast in the Netherlands. At this location a mega nourishment of 21 Mm{}^{3} named the Sand Engine was constructed. In this case we will explore to what extent nourishments can reduce the (dune and beach) erosion during a storm event.

You can work on the following assignments:

  1. Go to the folder “Examples\Nourishment case” and double click on the file “runall.bat”. This batch file will run three simulations sequentially in which the profile configuration varies and corresponds with the undisturbed profile (folder reference), a shoreface nourishment (folder shoreface) and a beach nourishment (folder beach) respectively. Each model will run for a few minutes. While running you can already answer question 2 to 6.
  2. For the reference case open the params.txt in which you specify model input files and settings. Check the number of grid-points in x-direction (keyword: nx) and y-direction (keyword: ny). How many directional wave bins are defined and what is their width (keywords: thetamin, thetamax, dtheta).
  3. Do the wave conditions change during the simulation? What is/are the wave height(s) and wave period(s) applied in the simulation?
  4. Does the storm surge level change during the simulation? What is the maximum surge height in the simulation. Surge height is defined with respect to the mean sea level (MSL)?
  5. What is the simulation time (keyword: tstop)? Do we apply a morphological acceleration factor (keyword: morfac)? What variables are stored as output and with what time interval? How much hydrodynamic time is simulated?
  6. Probably the simulation has finished. When you start the model, it generates a file named XBlog.txt. Open this file and check what is stored in the file. What was the total simulation time?
  7. Inspect the initial bathymetries of each simulation with QUICKPLOT. Choose Files of type “NetCDF files and GRIB files” and open “xboutput.nc” in the simulation folder).
    1. At what cross-shore position were the shoreface nourishment and beach nourishment placed?
    2. What is the (average) thickness of the nourishments?
    3. Is the volume of the nourishments comparable?
    4. Plot the reference profile with markers; does the grid resolution vary in cross-shore direction?
  8. Use the Quickplot tutorial and try to make an animation in which you plot short wave height (H), water level (including long wave variations, zs) and bed level (zb) as function of time.
  9. Plot the offshore water level as function of time. Also open the file “tide.tek” (Tekal data files format), which contains the imposed surge level. Did the model correctly simulate the imposed surge level?
  10. Inspect the final bathymetries of each simulation.
    1. What is the dune face retreat in the three simulations you have carried out?
    2. Where does the eroded sediment form the dunes deposit?
    3. What nourishment type is most effective in reducing the impact of a storm and do you have an explanation for this?
  11. In the folder “banquette” you find a final simulation in which a special beach nourishment type is evaluated named a banquette. This beach nourishment has a highly elevated flat area that connects to the dune foot on which beach restaurants can be build.
    1. Run the model and compare in Quickplot the banquette design with the beach nourishment design we have evaluated before. Do you expect more or less erosion?
    2. Check your hypothesis by comparing the final profile of the banquette simulation to the other simulations.
    3. What would be your approach to further reduce beach and dune erosion?

Overwash at Santa Rosa Island , USA (2DH)

This case concerns overwash at Santa Rosa island in the Gulf of Mexico during hurricane Ivan in 2004.

You can work on the following assignments.

  1. For the reference case open the params.txt in which you specify model input files and settings. Check the number of grid-points in x-direction (keyword: nx) and y-direction (keyword: ny). How many directional wave bins are defined and what is their width (keywords: thetamin, thetamax, dtheta).
  2. In this simulation the grid is specified in Delft3D format. Open Quickin in the Delft 3D menu (Grid Quickin) and use the brief tutorial to read in the grid and bathymetry. Does the grid resolution vary in cross-shore direction? And in longshore direction? What are the minimum dx and dy? Why can the grid be coarse offshore?
  3. How many wave conditions do we apply in this simulation? What is the offshore mean wave direction? Does the surge level change in the simulation?
  4. What is the simulation time (hydrodynamic and morphologic)?
  5. Inspect the model results and make an animation of the short wave height (H) and the water levels (including long wave, zs). Describe what is happening.
  6. For the water levels set the color limits manual between -0.5 and 3.5.
  7. Make an animation of cumulative sedimentation/erosion. Describe what is happening.
  8. For the sedimentation/erosion set the color limits manual between -3 and 3
  9. Look at the mean flow field. Plot the flow field in colored vectors. Where are the flow velocities highest and what is the direction of the flow (cross-shore or longshore)? Is there (also) a longshore current present and what is its intensity?

If you have time left feel free to:

  1. Narrow or broaden the imposed spectrum by changing the parameter directional spreading (s) in ‘jonswap.inp’ (you could for example set s = 100 and s = 2 respectively). Make animations of the instantaneous short wave height to see what is happening to the size of the wave groups.
  2. Design a nourishment in Quickin to reduce the impact of the storm on Santa Rosa Island. Change the depth file in params.txt to make a simulation with the updated bathymetry.

Yanchep perched beach and natural breakwater (2DH)

This case is an example of a beach 60km north of Perth most commonly known as Yanchep lagoon. Many beaches in WA like Yanchep are fronted by shallow reef and here we are investigating the effects of the reef on the morphodynamics.

You can work on the following assignments:

  1. Go to the folder “Examples\YanchepBeach” and double click the file “run_model.bat”. The simulation will start (and will run about 15 minutes).
  2. Meanwhile, inspect the bathymetry file and the structure file (using Quickin). What is the depth in the lagoon? Is the reef enclosing the lagoon below or above the model initial water level? What is the wave height at the boundary condition?
  3. Use Quickplot and try to make an animation in which you plot short wave height (H), water level (including long wave variations) (zs) and Eulerian velocities (ue and ve) as function of time. What happens in the lagoon?
  4. Use Quickplot and try to make an animation of cumulative sedimentation/erosion. What happens in the lagoon?
  5. How is the lagoon affected by the mean water level? Increase or decrease the mean water level condition (‘tide.tx’), run the model again (maybe for a shorter time by reducing keyword: tstop). How are the circulation and sediment transport affected?
  6. What would happen if the lagoon was open at the southern end? Open the structure file (keyword: ne_layer=’reef.dep’) with the Quickin tool and modify it to allow the southern end of the lagoon to be eroded. Modify the param.txt file to use this new structure file and run the model. Alternatively, remove the reef from the bathymetry and rerun the model without the structure file, by setting the keyword struct=0.

If you still have time;

  1. Reefs are very rough what happens in the model when the friction is increased? Reduce the Chezy roughness and increase the value of f:math:`{}_{w}`. Rerun the model what do you observe?
  2. Is wave/current interaction (keyword: wci=1) switched on? Rerun the model with the wave/current switch on/off. Compare the output with model you ran previously. How much effect do you see on the morphology?