8.3 Experimental Methods
119
for varying extents of erosion control in designated small watersheds of the Loess
Plateau to investigate the relationship between the runoff and the sedimentation.
Rainfalls and soils similar to those of the prototype were applied, and the landforms
were scaled down according to the prototype in the above-mentioned experiments.
Nevertheless, no explicit scale relationship between the prototype and the model has
been reported in the above studies.
Xu et al. (2009) has proposed a semi-scale physical model experimental method
to simulate the soil and water process in small watersheds of the Loess Plateau, and
confirmed it with serial model experiments. The key idea of the method is that the
ratio of the modeled geomorphological evolvement rate to the corresponding rate
of the prototype should be kept constant after the determined runs of the rainfalls,
so that the soil and water erosion processes of the prototype could be represented
by the result of the model experiment. Four measures have been proposed to ensure
the ratio R a constant: (1) A bare land model with a corresponding erosion rate
should be applied in the experiments. (2) Dimensions of the landform, including the
check-dams, should normally be scaled down according to the prototype watersheds.
(3) Soil similar to those of the prototype should be used. (4) The antecedent water
content before each rainfall simulation should be kept constant. The proposed method
provides the quantitative proportion of soil loss between the prototype and model,
using similarity criteria. Nevertheless, it did not strictly meet the similar situation in
the conventional scale model experiment and could not provide the scale relationship
of the erosion depths between the model and the prototype, etc.
Two experiments were carried out to demonstrate the hydro-sedimentologic balance on the dam-land, one for a single check-dam via runoff simulation, and the
other for the check-dam system via rainfall simulation. The objectives of this study
are to prove the feasibility of the relative stability idea for check-dams from the point
of view of hydro-sedimentologic balance, and present a method for designing scale
model experiments on soil and water erosions.
8.3.1 Runoff Simulation
Generally, according to the correlative criterion (MWRC 2009), middle scale checkdams with dam heights of 15–25 m and reservoir capacities of 0.1–0.6 million m
3
should be built in the lower reaches of the main branch gullies. In the present study,
the hydro-sedimentologic process and the geomorphological variation for 18 runoffs
were investigated with a middle-scale check-dam of 21 m high, which was built near
the outlet of the lower reach of the Yangdaogbou Catchment.
Obviously, deposition on the dam-land is determined by its own reservoir capability as well as the quantity of water-solid mixture from the upper reaches, and is
independent of the source of the mixture, as these check-dams are small-sized reservoirs in nature. Thus, the effects of land use, vegetation, rainfall, etc., on soil and
water erosions could be embodied in the flux and concentration of the mixture, and
the latter could be calculated according to the prototype erosion rate. The Similarity
119
for varying extents of erosion control in designated small watersheds of the Loess
Plateau to investigate the relationship between the runoff and the sedimentation.
Rainfalls and soils similar to those of the prototype were applied, and the landforms
were scaled down according to the prototype in the above-mentioned experiments.
Nevertheless, no explicit scale relationship between the prototype and the model has
been reported in the above studies.
Xu et al. (2009) has proposed a semi-scale physical model experimental method
to simulate the soil and water process in small watersheds of the Loess Plateau, and
confirmed it with serial model experiments. The key idea of the method is that the
ratio of the modeled geomorphological evolvement rate to the corresponding rate
of the prototype should be kept constant after the determined runs of the rainfalls,
so that the soil and water erosion processes of the prototype could be represented
by the result of the model experiment. Four measures have been proposed to ensure
the ratio R a constant: (1) A bare land model with a corresponding erosion rate
should be applied in the experiments. (2) Dimensions of the landform, including the
check-dams, should normally be scaled down according to the prototype watersheds.
(3) Soil similar to those of the prototype should be used. (4) The antecedent water
content before each rainfall simulation should be kept constant. The proposed method
provides the quantitative proportion of soil loss between the prototype and model,
using similarity criteria. Nevertheless, it did not strictly meet the similar situation in
the conventional scale model experiment and could not provide the scale relationship
of the erosion depths between the model and the prototype, etc.
Two experiments were carried out to demonstrate the hydro-sedimentologic balance on the dam-land, one for a single check-dam via runoff simulation, and the
other for the check-dam system via rainfall simulation. The objectives of this study
are to prove the feasibility of the relative stability idea for check-dams from the point
of view of hydro-sedimentologic balance, and present a method for designing scale
model experiments on soil and water erosions.
8.3.1 Runoff Simulation
Generally, according to the correlative criterion (MWRC 2009), middle scale checkdams with dam heights of 15–25 m and reservoir capacities of 0.1–0.6 million m
3
should be built in the lower reaches of the main branch gullies. In the present study,
the hydro-sedimentologic process and the geomorphological variation for 18 runoffs
were investigated with a middle-scale check-dam of 21 m high, which was built near
the outlet of the lower reach of the Yangdaogbou Catchment.
Obviously, deposition on the dam-land is determined by its own reservoir capability as well as the quantity of water-solid mixture from the upper reaches, and is
independent of the source of the mixture, as these check-dams are small-sized reservoirs in nature. Thus, the effects of land use, vegetation, rainfall, etc., on soil and
water erosions could be embodied in the flux and concentration of the mixture, and
the latter could be calculated according to the prototype erosion rate. The Similarity