GSSHA Survival

Good Advice

  1. When delineating your watershed do not use too small of a threshold for creating streams.  Having a more detailed stream network can make setting up streams more difficult.
  2. Create your grid and then use a uniform roughness and rainfall to be sure surface flow is okay.
  3. Use CleanDam and not TOPAZ to fix digital dams
  4. It won’t hurt to edit a few of the ponding locations by hand
  5. When defining streams
    1. Make sure the last node (outlet) is over the outlet grid cell (at least be sure it doesn't inherit a bogus elevation)
    2. Redistribute vertices to a distant greater than the grid cell size
    3. If needed realign the streams to follow the contours of the grid cells (they should be close but if the grid size is greater than the DEM they could be off a little).
    4. Smooth streams. It is helpful to smooth over multiple stream arcs to provide better continuity. Make sure stream nods are below grid cells.
    5. Make sure your cross sections are large enough to convey the flow.  If water is spilling back on to the overland grid cells you could see problems.
    6. Be sure you turn on stream routing in Job Control, and stream depth/flow output in the Output Control
  6. Save your running model with streams as your base case from which you can build other simulations on.
  7. If you have high gradients of rainfall input (like a Type II temporal distribution) you may need to adjust your time step down (1-3 seconds may be necessary if you see numerical oscillations in your resulting hydrograph).
  8. Be sure you define rainfall input as incremental values in millimeters.

 

Working around known bugs in WMS 8.0 (Feb. 21,2008)

  1. You must save your project before running CleanDam.
  2. When running CleanDam be sure to enter a new elevation file name
  3. Replace elevations after CleanDam runs.
  4. Never save your project with an Index data set Active (displayed)
  5. When saving a project with a gage for the first time check to be sure the directory path name is correctly defined for the gage
  6. Reading simulations with defined gages causes the streams to be lost.  Therefore it is important to follow step 6 above so you can build from that point.  You can import .gag files previously created.