a reach or total length of river. Einstein, Colby, and Manning's equations deal with depth of
flow, width of flow and energy slope whereas most geomorphic equations deal with channel
depth, channel width and channel slope.
The interdependency of top width, depth of flow, energy slope, bed-material size, and
kinematic viscosity on the water and sediment discharge allows the establishment of the
relative influence of those variables on stage-discharge relationships. This information can be
used to establish the direction of variation of hydraulic variables as a consequence of changes
imposed on the bed-material and sediment discharge as shown in Table 5.5.
Table 5.5. Qualitative Response of Alluvial Channels.
Change in
Effect On
Magnitude of
Variable
Regime
River
Energy
Stability of
Variable
of Flow
Form
to Flow
Slope
Channel
Area
Stage
-
-
+
+
Discharge
(a)
+
+
M→B
+
+
-
-
(b)
-
-
B→M
+
+
Bed Material
(a)
+
-
M→B
+
+
-
-
Size
(b)
-
+
B→M
-
-
Bed Material
(a)
+
+
B→M
-
-
+
-
-
Load
(b)
-
-
M→B
+
+
-
+
+
-
-
Washload
(a)
+
+
-
-
+
+
(b)
-
-
+
+
-
-
Viscosity
(a)
+
+
-
-
+
+
(b)
-
-
+
+
Seepage Force
(a)
Outflow
-
B→M
+
-
+
+
+
(b)
Inflow
+
M→B
-
+
-
-
-
Vegetation
(a)
+
-
B→M
+
-
+
+
+
(b)
-
+
M→B
-
+
-
-
-
Wind
(a)
Downstream
+
M→B
-
+
-
-
-
(b)
Upstream
-
B→M
+
-
-
+
+
Chapter 4 indicates that the wash load increases the apparent viscosity of the water and
sediment mixture. This makes the bed material behave as if it were smaller. In fact, the fall
diameter of the bed material is made smaller by significant concentrations of wash load. With
more wash load, the bed material is more susceptible to transport and any river carrying
significant wash load will change from lower to upper regime at a lower Froude number than
otherwise. Also, the viscosity is affected by changes in temperature.
Seepage forces resulting from seepage losses help stabilize the channel bed and banks. With
seepage inflow, the reverse is true. Vegetation adds to bank stability and increases resistance
to flow, reducing the velocity. Wind can retard flow, increasing roughness and depth, when
blowing upstream. The reverse is true with the wind blowing downstream. Wind generated
waves and their adverse influence on channel stability are the most significant effects of wind.
5.33
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