Er Yang

Using 137Cs to quantify the sediment delivery ratio in a small watershed

Understanding the sediment delivery ratio (SDR) is important in controlling sediments for the sustainable development of natural resources and in the design of the construction such as dams and reservoirs. The purpose of this investigation is to determine the SDR by the (137)Cs tracing method in a small watershed in the Sichuan Hilly Basin of China. In the study watershed, different land plots are divided according to the land use type, and 97 sampling sites were selected from these plots. The results show that the average net soil loss rates from the forest land and sloping cultivated land are 1759 and 4468t/km(2)a, respectively. No (137)Cs was detectable on the bare rock surfaces and previous work showed that the erosion rate from the bare rock area was 14,260t/km(2)a. In the depositional zone, the sedimentation rates in the Caoto (a kind of cultivated land located at the foot of hills) and paddy field are 3113 and 3562t/km(2)a, respectively. Combining the area of each land use in the small watershed, the SDR of 0.40 is obtained in the past four decades. The (137)Cs technique was shown to provide an effective and rapid means of estimating the SDR within the small watershed.

Transformation of the Raindrop Speed Base on Diameter about Soil Erosion Similar

Simulate rain experiment method was adopted to study the transformation of the change of raindrop speed and diameter with time and the results indicated that the rain intensity change strongly with time at the natural rainfall, However, the rain intensity was stability at simulate rainfall. At the natural rain, the raindrop speed mainly at 0.4-6.6m/s in different time, it have two wave crest were 1m/s and 3.4m/s. However, at the simulate rain, the raindrop speed mainly at 0.2-5.8m/s in different time; it has one wave crest was1m/s.In natural rain and simulate rain, the 0.125mm diameter raindrop speed were about at 0.4-2.6m/s and0.8-5.8m/s, the 0.25mm diameter raindrop speed was about at 0.6-2.6m/s and 0.6-5.8m/s, the 0.375mm diameter raindrop speed was about at 1-1.8m/s and0.4-2.2m/s, the 0.5mm diameter raindrop speed was about at 1-3.4m/s and 0.2-1.8m/s, the 0.75mm diameter raindrop speed was about at 3.4-4.2m/s and1-3.4m/s, the 1mm diameter raindrop speed was about at 3.4-4.2m/s and 1-3.4m/s, the 1.25mm diameter raindrop speed was about at4.2-5m/s and1-5m/s, the 1.5mm diameter raindrop speed was about at5m/s and 2.6m/s.

Effect of Grass Coverage on the Sediment Concentration in Overland Flow in the Hillslope-Gully Side Erosion System

By scouring experiments, the changeable process and characteristics of sediment concentration in sloping surface with different coverage degrees and spatial locations of grass were studied. Five grass coverage degrees of 0, 30%, 50%, 70%, 90%, three spatial locations of grass (upslope, mid-slope, low-slope) and two water inflow rates of 3.2L/min, 5.2L/min were applied to a 0.5 by 8 m soil bed in scouring experiments. Results showed that in the hillslope–gully side erosion system, the grass coverage has great effect on reducing the sediment concentration in the overland flow when the water inflow rate is small, but when the water inflow rate is large this kind of effect is very limited. When the grass located at the low-slope on the hillslope the sediment concentration is relatively smaller. The sediment concentration in the overland flow is gradually decreasing with the duration of scouring, and the effect of spatial locations of grass on the temporal variation of sediment concentration is very complicated because of gully erosion.

Effect of Grass Coverage on the Sediment Concentration in Overland Flow

By scouring experiments, the changeable process and characteristics of sediment concentration in sloping surface with different coverage degrees and spatial locations of grass were studied. Five grass coverage degrees of 0, 30%, 50%, 70%, 90%, three spatial locations of grass (upslope, mid-slope, low-slope) and two water inflow rates of 3.2L/min, 5.2L/min were applied to a 0.5 by 4 m soil bed in scouring experiments. Results showed that the sediment concentration in overland flow obviously decreased with increasing grass coverage degree during the scouring experiments. When the grass coverage degree is over 30%, the grass can play obvious role in reducing the sediment concentration, and along with the increase of grass coverage degree the role became more and more obvious, particularly when the grass coverage degree reached to 70%. The spatial location of grass on the sloping surface has little effect on the sediment concentration in overland flow.