Stability of the relocated channel, which is substantially more narrow than specified in the
plans and also more narrow than the natural channel, is attributed to the resistant clay in the
bed and lower banks. Evidently because of mowing of the median area, no trees have
become established along the bankline.
9.5.14 Gravel Mining on the Russian River, California (Example 14)
It is essential to monitor and manage sand and gravel mining so as not to induce undesirable
instabilities in the river system. In most cases, removal of sand and gravel has caused
deepening and widening of the channel. These wider, deeper reaches act as sinks for the
sediment loads and they may trap the finer clays and silts, altering the river environment. An
interesting example of a river where excessive removal of sands and gravels has caused
significant changes is in the vicinity of the confluence of Dry Creek with the Russian River.
The location map is shown in Figure 9.15a. The tributary (Dry Creek) enters the river just
downstream of a small dam on the Russian River. Previous sand and gravel extraction in the
tributary has not exceeded the calculated safe yield, however, extraction rates in the middle
reach of the Russian River significantly exceeded the safe yield for the period 1951 to 1964.
This excessive extraction of sand and gravel induced a headcut that progressed upstream
along the tributary, as shown in Figures 9.15b and 9.15c. This headcut was curtailed by a
rock outcrop acting as a control point near a bridge approximately seven miles upstream of
the confluence and essentially stabilized around 1972-1973. During the years 1946 to about
1955, the tributary channel widened (Figure 9.15d). Figure 9.15e shows the corresponding
stage discharge relationships of the Russian River at the mouth of Dry Creek. Although in
this example both rivers are bar-braided systems, they indicate the magnitude of possible
adverse consequences from excessive sand and gravel mining on meandering streams.
Figure 9.15. Case study of sand and gravel mining (Example 14).
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