40
Tecnología y Ciencias del Agua
, vol. VIII, núm. 2, marzo-abril de 2017, pp. 31-41
Li
et al
.,
Particle size distribution and settling velocity of sediments in water diverted from the Yellow River during border-strip irrigation
•
ISSN 2007-2422
velocities of particles of different sizes were
calculated using the formula presented in
Section of Calculation methods. The settling
velocity was found to be affected primarily by
the sediment’s density and particle size, water
temperature, water depth, and strip width.
The density of the sediment did not change as
the irrigation water moved forward. After the
water was channeled to the field, the water
temperature tended to remain stable, rendering
its influence on the water flow negligible. The
water depth and the strip’s slope changed a lot
during the advance of the irrigation water, and
water depth also affected the friction velocity of
the flow (
U
=
gHj
) and the Shields number (
Q
=
D
hJ
/
D
). Water depth in the formula canceled
out during the formula derivation, implying
that it has no influence on settling velocity.
However, the strip’s slope varied significantly
along the strip length and the slope variation
was closely correlated with the settling veloc-
ity. Ultimately, particle size was the main factor
affecting the settling velocity of the sediment
in the irrigation water: The settling velocity
decreased as the particle size decreased.
Conclusions
During the border-strip irrigation experiment,
the amounts of settled sediment varied signifi-
cantly from the top ends of the strips to their
bottom ends. The amounts of sediment settled
at the top ends of the wide strip and narrow
strip were, respectively, 4.2 times and 5.3 times
the amounts settled on the bottom ends. The
advance rate of the sediment also changed sig-
nificantly from the top end to the bottom end
of each strip, indicating that the advance rate
was affected not only by the strip’s slope, but
also by the flow rate and infiltration of water
into the soil.
The amounts of deposited particles de-
creased along the strip length from top to bot-
tom. The decrease was especially marked on
section of each strip between 40 and 120 m.
The particle size distribution of the sedi-
ments deposited along the strips accords with
the law of sedimentation; coarse particles ac-
cumulated primarily at the top ends as a result
of high settling velocity. The existence of coarse
particles in the sediment at the bottom ends
suggests that the advance of irrigation water
was a relatively complex process associated
with the scouring action of the water flow on
the surface particles deposited on the strips.
Further research is needed to explore this issue.
It was feasible to represent the water flow
over the strips as open-channel flow when
calculating the settling velocity of the sediment
particles. However, the formula for calculating
settling velocity requires further modification to
take into account the influences of flume rate as
well as the scouring action of the moving water
on the surface sediment deposited on the strips.
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