Prediction Of Sediment Delivery Rate

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Rate of sediment accumulation in a reservoir can be found by two methods.
One approach depends on historical records of the silting rate for existing reservoirs and is purely empirical. The second general method of calculating the sediment delivery rate involves determining the rate of sediment transport as a function of stream discharge and density of suspended silt.

The quantity of bed load is considered a constant func- tion of the discharge because the sediment supply for the bed-load forces is always available in all but lined channels. An accepted formula for the quantity of sediment trans- ported as bed load is the Schoklitsch formula:

G_b=86.7*S^3/2 (Q_i – bq_o)/ ? D_g

where
G_b= total bed load, lb/s (kg/s)

D_g =effective grain diameter, in (mm)

S= slope of energy gradient

Q_i= total instantaneous discharge, ft3/s (m3/s)

b =width of river, ft (m)

q_o =critical discharge, ft3/s (m3/s) per ft (m), of river width
=

(0.00532/S^4/3)D_g

An approximate solution for bed load by the Schoklitsch formula can be made by determining or assuming mean values of slope, discharge, and single grain size representative of the bed-load sediment. A mean grain size of 0.04 in (about 1 mm) in diameter is reasonable for a river with a slope of about 1.0 ft/mi (0.189 m/km).

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