Geoscience Reference
In-Depth Information
Figure 9.12 Sensitivities of model results in Taipei case to (a) adaptation coefficient α 0 ,
(b) adaptation length L b , (c) Manning n , and (d) coefficient k t (Wu and Wang, 2007).
increases from 2.0 to 4.0 and L b increases from 0.25 to 0.5m, the simulated water and
bed surface profiles change locally, especially upstream of the dam site. The influences
of coefficients
0 and L b on the simulated water and bed surfaces are thus at limited
levels. As the Manning n increases from 0.025 to 0.035, the simulated water and bed
surfaces vary very little, and the wave front slightly slows down. The model results
are not particularly sensitive to variation in the Manning n values. As the correction
factor k t increases from 1
α
f , the maximum erosion depth
increases by 21%. The evaluation of k t is important to the erosion magnitude. The
test shows that k t
+
1.0
ρ
f to 1
+
2.0
ρ
s
s
=
1
+
1.5
ρ
f provides reasonable results.
s
9.3 SIMULATION OF DAM SURFACE EROSION
DUE TO OVERTOPPING FLOW
Flow overtopping earth dams and levees can cause serious erosion and even wash
out the structures. Compared to the dam-break flow case, the sediment transport
and morphological change due to overtopping flow may be less intensive. However,
the overtopping flow is usually in mixed regimes, and the interactions among flow,
sediment transport, and bed change are still appreciable. These should be considered
in the simulation of overtopping flow and the associated erosion process.
Tingsanchali and Chinnarasri (1999) simulated the dam surface erosion process
due to overtopping flow, but their model ignores the effects of sediment transport and
bed change on the flow and uses the assumption of local equilibrium sediment trans-
port. This erosion process herein is simulated using a more advanced model, which
computes the flow using Eqs. (9.59) and (9.60) and the bed-material load transport
 
Search WWH ::




Custom Search