05 February 2019

Version 2-0-0 of the Simplified Dam Break Model (SDB) is available for release.  Key enhancements include error checking, a metric option, and minor algorithm changes.  Some of the changes made to this version may result in slight changes in the output when SDB (2019) is compared to NWS SMPDBK and SDB (2009).  This is due to corrections made as stated below.  SDB Version 2-0-0 has been extensively tested using over 100 datasets and is more robust than any version of the SMPDBK model since its development.

All release versions of SDB have been tested and compared to the results of NWS SMPDBK (1991).

SDB-J (Version 2-0-0) has been modified to reflect changes in SDB.  Also, the ability to export a FLDWAVE file was added to the GUI.


Changes in SDB and SDB-J Version 2-0-0

The following changes have been made to SDB since the 2009 release.  Due to the nature of the changes, both SDB and SDB-J have been changed.

Point of Interest Message – The message stating that the point of interest has been moved always printed out in NWS SMPDBK.  In SDB, the message prints out only if the point of interest is not located at any of the actual cross sections.  A different message displays if no point of interest is given.

Negative Breach Width – The breach width is properly set to |BW| when a negative value is read in for a concrete arch dam (IDAM=2).  This switch prevents SDB from modifying the breach width when the cross section is too narrow.  Previously, a negative BW was treated as BW=0 and a default value was computed.  This correction may cause a slight change in the computed outflow which also may affect the change in peak water surface elevation when IDAM=2.

Convergence Iterations – The maximum number of iterations allowed when computing the submergence correction has been increased from 15 to 25.  This correction may cause a slight change in routed peak flows which also may affect the change in peak water surface elevations when non-convergence occurred previously. 

Cross Section Location Name (TWN) – A name for each cross section location has been added as an input parameter to allow for future GIS integration.  If the name is left blank, it is generated using the river location.

Metric Option (METRIC) – The input and output may now be displayed in metric units.  The input parameters (in metric units) are converted to English units for computations.  Although the computations are done in English units, all output information, including debug information, is displayed in metric units.

Obsolete Parameters – Obsolete parameters were either removed or reassigned.  When running existing data sets, the user should verify that the dam type (IDAM) is correct.

gFortran90 Compiler – The code has been modified to be gFortran90 compliant.  This includes initializing parameters, changing read/write statements, and formatting.  These improvements allowed several problematic data sets to run successfully.

Export FLDWAVE File – SDB-J will export a FLDWAVE text file with a “.fwd” extension which can be run by the FLDWAVE model.  The following assumptions have been made regarding FLDWAVE parameters.  After a successful run of the FLDWAVE model with the file exported from SDB-J, the following parameters should be modified.

  • TEH (DG 7) – The run period is 1.5 times the time to peak of the downstream water level.  This parameter may need to be increased to allow the falling limb of the downstream hydrograph to be reached.
  • DXM (DG 19) – The distance interval is computed using the equation  where c is the distance interval divided by the difference between the times to the peak water level at adjacent cross sections, and  is the time of failure in hours (TFH)/20.  The DXM values are usually much smaller than they need to be. The values should be adjusted according to the recommendations in the FLDWAVE output.
  • SAR (DG 26) vs HSAR (DG 27) – The Surface Area – Elevation table consist of two points.  This table may not adequately represent the volume of the reservoir.  Preferably, the actual table should be used.  If the table does not exist, it can be created by generating a table of values that result in the outflow volume matching the reservoir volume.  The outflow volume is computed in FLDWAVE and shown in the output file when JNK ≥ 4.  The base flow volume should be subtracted from the outflow volume before comparing it to the reservoir volume.
  • HDD (DG 28) – The height of the dam is set equal to the pool level.  If piping failure is the failure mode or if the pool level is above the dam crest, HDD should be set back to the actual top of dam elevation.
  • CLL (DG 28) – The crest length is set equal to 3 times the height of the dam.  It should be reset to the actual crest length.  If piping failure is modeled as overtopping failure, the crest length should be set to the length of the dam at the pool level.
  • QTD (DG 28) – The turbine flow is equal to the initial inflow hydrograph value.
  • ST1 (DG 58) – The inflow hydrograph is a steady-state value equal to 1% of the peak flow.  This value may be decreased if a minimum base flow is desired.  Also, if the routing reach is complex and the time of failure is short, the base flow may need to be increased for stability reasons.
  • T1 (DG 59) – The time period for the inflow hydrograph goes from 0 to TEH.


Known Bugs

Any directory accessed by the program cannot have spaces in it.


System Information

Operating Systems – Windows 2000, XP, Vista, Windows 7-10.  Windows processor can be 32-bit or 64-bit.
                                     Linux Fedora 27 with 64 bit processor.