When there is a significant change in discharge or sediment load, due
to flood, for example, erosion and deposition cause the geometry of an
,alluvial channel to change rapidly in order to achieve a new equilibrium
condition. Because the process is a highly complex multi-component,
multi-dimensional, and time-dependent process, its complete mathematical
modeling is not feasible at the present time.
In order to predict the variations of channel width, as well as the
river bed elevation, it is necessary to distinguish the sedimentation at the
bank from that of the bed. The Bureau of Reclamation GST ARS model
adopts a new concept which combines the conventional one-dimensional flow
model with the theory of minimum energy dissipation rate such that the
variation in channel shape can be calculated efficiently. A detailed
description of the original GSTARS model is given in the User's Manual of
the Bureau of Reclamation .
Because the GSTARS model is relatively new, the Bureau of
Reclamation decided to carry out some case studies in order to verify and
improve the model. The first case study, the erosion of the unprotected
spillway of Willow Creek Dam in Montana due to hypothetical floods, was
completed in April, 1987 . Because there were no erosion data due to
the hypothetical floods, the accuracy of the results could only be judged
qualitatively and by comparing with other estimates. The results appeared
quite reasonable and encouraging.
The actual channel erosion of Mescalero Dam emergency spillway in
New Mexico due to the 1984 flood has been selected as the subject of the
second case study. The topographic data taken on June 12, 1979 was used
as the initial condition. The water level data taken during the 1984 flood
was used to calculate the flood hydrograph. In addition, sediment samples
were taken and analyzed and used as input data. Four channel cross
sections measured immediately after the 1984 floods were used to determine.
the accuracy of the model output.
During the course of the second case study; it was necessary to add
three new features to the GSTARS model. The three new features are, in
order of importance, (1) the bank slope stability constraint, (2) the erosion
due to water fall at the upstream end, and (3) the lateral sediment
transport due to secondary current in a bend. With these additional
features, the modeled results agreed very well with field data, except at a
station where a branch channel meets the main channel. The present
GST ARS model is not capable of modeling channel junctions.
U.S. Department of the Interior
Bureau of Reclamation
Denver Federal Center
Song, Charles C. S.; Zheng, Yifan.
Application of Bureau of Reclamation's GSTARS To Lake Mescalero Dam Spillway.
St. Anthony Falls Laboratory.
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