Watson *et al. *(1997) found that the skewness of the flow distribution was strongly related to

sediment yield. Skewness, as defined by Chow (1964) is a measure of the lack of symmetry of a

distribution. For example, with the coefficient of skewness, Cs, at zero (Cs = 0), the distribution is

symmetric; with Cs > 0, the distribution is skewed to the right with a long tail on the right side; and with Cs

< 0 the distribution is skewed to the left. Figure 6.19 depicts the relationship developed by Watson *et al.*

(1997) between the skewness of the flow distribution for the 15-minute data, and the annual sand yield per

unit area for nine streams within the DEC watersheds in Mississippi. A trend of increasing sediment yield

with increasing skewness is evident. The outlier, Hickahala Creek, has an anomalously high, and

unexplained, sand yield. Figure 6.19 indicates that within the channelized DEC streams, the sand yield

(tons per acre) increased by a factor of almost ten for a three-fold increase in skewness. As the peak

discharge of a watershed increases due to land use change, channelization, or channel incision, the

skewness increases. Conversely, the decrease in the peak discharges associated with flow control will

reduce the skewness of the flow distribution, and result in a reduction in the downstream delivery of

sediment.

Figure 6.19 Annual Sediment Load as a Function of Flow Distribution

Skewness

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