124
8 Sediment-Storage Effects of Check-Dam …
Fig. 8.4 Simulated rainfall was applied on the model check-dam system
an equal antecedent soil moisture before the commencement of the experiment in the
same series of rainfall applications. An equal period (24 h) was kept after each rainfall, and the water content was kept almost constant, except in the first experiment.
Soil samples and test beds were initially protected by plastic sheets until the rainfall
intensity was correctly adjusted and the data logging equipment was operating satisfactorily. Then the cover was removed suddenly and the test was started. During
each rainfall application, the total water-solid mixture was collected in the calibrated
tank and the runoff container at the outlet of the plot. Runoff samples were also collected with a sampling bottle of 100 ml for determining the sediment concentration.
The flow rate was also measured using the calibrated bucket every 2 min. After the
experiment, the deposited bed load was dried and weighted, and the weight of the
suspended load was calculated from the concentration determined gravimetrically
and from the volume measured by the bucket gauge. The microrelief of the gully
bed, which was digitized in the horizontal directions in 0.1 m grids, was measured
by the height finder. The dam-land area after each rainfall was measured by means
of a digital camera and a wooden frame with a known dimension. The wooden frame
was placed flatwise on the dam-land, which was proportionally deformed with the
dam-land in the plan-photo. Then the areas of the dam-land and the wooden box in
the photo could be calculated respectively via the AutoCAD program, and the result
so obtained was the practical area of the dam-land.
Before the above scenario demonstration as the dams were built orderly, the ratio
of the erosion extents between the prototype and the model for each run of rainfall
should be verified. An identifying test of simulated rainfall before the construction of
the dams, in which the geometrical scale, the antecedent land cover and the rainfall in
the identifying test were homologous to those of the above experiment for the dams,
8 Sediment-Storage Effects of Check-Dam …
Fig. 8.4 Simulated rainfall was applied on the model check-dam system
an equal antecedent soil moisture before the commencement of the experiment in the
same series of rainfall applications. An equal period (24 h) was kept after each rainfall, and the water content was kept almost constant, except in the first experiment.
Soil samples and test beds were initially protected by plastic sheets until the rainfall
intensity was correctly adjusted and the data logging equipment was operating satisfactorily. Then the cover was removed suddenly and the test was started. During
each rainfall application, the total water-solid mixture was collected in the calibrated
tank and the runoff container at the outlet of the plot. Runoff samples were also collected with a sampling bottle of 100 ml for determining the sediment concentration.
The flow rate was also measured using the calibrated bucket every 2 min. After the
experiment, the deposited bed load was dried and weighted, and the weight of the
suspended load was calculated from the concentration determined gravimetrically
and from the volume measured by the bucket gauge. The microrelief of the gully
bed, which was digitized in the horizontal directions in 0.1 m grids, was measured
by the height finder. The dam-land area after each rainfall was measured by means
of a digital camera and a wooden frame with a known dimension. The wooden frame
was placed flatwise on the dam-land, which was proportionally deformed with the
dam-land in the plan-photo. Then the areas of the dam-land and the wooden box in
the photo could be calculated respectively via the AutoCAD program, and the result
so obtained was the practical area of the dam-land.
Before the above scenario demonstration as the dams were built orderly, the ratio
of the erosion extents between the prototype and the model for each run of rainfall
should be verified. An identifying test of simulated rainfall before the construction of
the dams, in which the geometrical scale, the antecedent land cover and the rainfall in
the identifying test were homologous to those of the above experiment for the dams,