sediment load:
Amount of sediment being moved by a stream.
sediment yield:
The total sediment outflow from a watershed or a drainage
area at a point of reference and in a specified time period. This
outflow is equal to the sediment discharge from the drainage
area.
seepage:
The slow movement of water through small cracks and pores
of the bank material.
shear stress:
See unit shear force.
shoal:
A relatively shallow submerged bank or bar in a body of water.
sill:
(a) A structure built under water, across the deep pools of a
stream with the aim of changing the depth of the stream; (b) A
low structure built across an effluent stream, diversion channel
or outlet to reduce flow or prevent flow until the main stream
stage reaches the crest of the structure.
silt:
A particle whose diameter is in the range of 0.004 to 0.062
mm.
sinuosity:
The ratio between the thalweg length and the valley length of a
stream.
slope (of channel
Fall per unit length along the channel centerline or thalweg.
or stream):
slope protection:
Any measure such as riprap, paving, vegetation, revetment,
brush or other material intended to protect a slope from
erosion, slipping or caving, or to withstand external hydraulic
pressure.
sloughing:
Sliding or collapse of overlying material; same ultimate effect
as caving, but usually occurs when a bank or an underlying
stratum is saturated.
slope-area method:
A method of estimating unmeasured flood discharges in a
uniform channel reach using observed high-water levels.
slump:
A sudden slip or collapse of a bank, generally in the vertical
direction and confined to a short distance, probably due to the
substratum being washed out or having become unable to bear
the weight above it.
soil-cement:
A designed mixture of soil and Portland cement compacted at
a proper water content to form a blanket or structure that can
resist erosion.
sorting:
Progressive reduction of size (or weight) of particles of the
sediment load carried down a stream.
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