FLOOD06918

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: The NWS Simplified Dam Break-Flood Forecasting Model
• Date: 5/16/1986
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

The third version of the model, or the "micro-BASIC" version, has been
developed for use on micro-computers with BASIC compilers. This version
performs the same computations and requires the same data input as the
FORTRAN version and its storage requirements are small enough for it to fit
on most micro-computers. The "short" option available in the FORTRAN
version is provided in this version as well. Also, a hybrid of this version
has been developed for use on a hand-held, programmable computer (See
Appendices IlIa and IV). A listing of the BASIC code and an example run is
included in Appendix III.

IV. CONCLUDING REMARKS

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In both real-time forcasting and disaster preparedness planning, there
is a clear need for a fast and economical method of predicting dam-break
floodwave peak stages and travel times. The SMPDBK model fills this need,
producing such predictions quickly, inexpensively and with reasonable
accuracy. For example, in test analyses of the Teton and Buffalo Creek dam
failures, approximating the channel as a prism, calculating the maximum
breach outflow and stage at the dam, defining the routing parameters, and
evaluating the peak stage and travel time to the forecast points required
less than 20 minutes of time with the aid of a non-programable hand-held
calculator while the average error in forecasted peak flow and travel time
was 10-20% with stage errors of approximately 1 ft. Furthermore, compari-
sons of SMPDBK model results with DAMBRK model results from test runs of
theoretical dam breaks show the simplified model produces average errors of
10% or less. The authors had the advantages, however, of prior experience
with the model and possession of all required input data, the collection of
which consumes precious warning response time in a dam-break emergency.

To help reduce the time required for data collection, default values
for some of the input data are presented in Appendix I. These default
values may be used by dam-break flood forecasters when time is short and
reliable data are unavailable. Additionally, to help further reduce. the
time needed to employ the model, computerized versions of the model have
been developed for FORTRAN-compatible mini-computers and for BASIC language
micro-computers and programmable hand-held computers (see Appendices II and
III.)

..

The SMPDBK model is not only useful in a dam-break emergency, it is
also suitable for pre-computation of flood peak elevations and travel times
prior to a dam failure. Pre-computation of dam failures allows those
responsible for community preparedness to delineate danger areas downstream
should the dam fail. Ideally, to obtain the most reliable estimate of
probable flood elevations and travel times, the sophisticated NWS DAMBRK
model would be used in a long-term disaster preparedness study where
sufffcient computer resources are available. However, for short term
studies with limited resources, the SMPDBK model will be most helpful in
defining approximate peak stages, discharges, and travel times.

In closing, the authors would like to stress that while the SMPDBK
model can be a very useful tool in preparing for and during a dam failure
event, the user must keep in mind the model's limitations (Fread 1981).
First of all, as with all dam breach flood routing models, the validity of
the SMPDBK model's prediction depends upon the accuracy of the required

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