Effect of Check Dam on Sediment Load Under Vegetation Restoration in the Hekou-Longmen Region of the Yellow River

With years of vegetation restoration and check dam construction on the Loess Plateau, the sediment load of the middle reaches of the Yellow River have decreased sharply; however, the effects of check dam on this decrease of sediment load with such extensive vegetation restoration remains unclear. In order to further clarify the effects of check dam on sediment load reduction under vegetation restoration, we calculated vegetation coverage and check dam index based on multi-source remote sensing data, and calculated sediment reduction rate caused by human activities by Mann-Kendall statistical test and double cumulative curve, then established regression equations incorporating the check dam index and the sediment reduction rate using data from different geomorphic regions with different vegetation coverages. The results showed that sediment load in the Hekou-Longmen region and its 17 tributaries decreased significantly every year, and the change in sediment load could be divided into 3 typical periods: the base period (P1), the period mainly impacted by check dam construction (P2) and the period with comprehensive impact of check dam construction and vegetation restoration (P3). Compared with sediment load of the tributaries during P1, the sediment load decreased by 60.96% during P2 and by 91.76% during P3. Compared with the contribution of human activities to the reduction in sediment load in P2, the contribution of human activities in P3 increased significantly, while that of precipitation decreased slightly. The sediment reduction effect of check dams is greater in basins with low vegetation coverage than in basins with high vegetation coverage. There are differences in sediment reduction effect of vegetation restorations in different geomorphic regions, and the effect of vegetation restoration alone have certain upper limits. Such as, the upper limit of sediment reduction rate of vegetation restoration for rivers flowing through the sandstorm region is 47.86%. Hence, only combined the construction of check dam with vegetation restoration can it achieve more significant sediment reduction benefit and control soil erosion more effectively.

Experimental Study on the Compaction and Deformation of Filling Gangue by Reducing Waste Gangue for Filling Mining

The coal mining technology of fully mechanized solid filling is an efficient and green mining method that integrates “sediment reduction” and “emission reduction.” However, the discharge of wasted gangue and surface subsidence are controlled by the amount of wasted gangue used in filling mining and the compaction rate of gangue filled into a goaf, respectively. To increase the consumption of wasted gangue and reduce surface subsidence, mixed gangue composed of equal-quality washed gangue and crushed gangue is proposed as a raw material for solid filling on the basis of gradation theory. Next, a screening experiment was performed to analyze the grain gradation of different specimens, and a compression experiment was executed to compare and analyze the compression characteristics. The results show that the nonuniformity coefficient of mixed gangue is 55.2 and the curvature coefficient is 1.53, which significantly improve the grain gradation of washed gangue. The degree of relative compaction of mixed gangue is 1.226, which is significantly lower than that of washed gangue, which is 1.33. The deformation modulus of mixed gangue is 23–135 MPa, which is better than that of washed gangue (26–100 MPa), indicating that the compressive resistance of mixed gangue is significantly improved. The case study of the Tangkou mine suggests that mixed gangue greatly promotes the consumption of wasted gangue and can effectively control the surface deformation.

Pemanfaatan Sedimen Sungai Untuk Bahan Baku Unfired Bricks (Bata Tanpa Bakar)

The land use change in a watershed cause erosion resulting in sedimentation in river channels. Physically treatment of sedimentation requires a considerable cost, hence it is necessary to find another alternative treatment, i.e. by utilizing river sediment for building materials. Brick is a building material that is widely produced and used by the society. To provide solutions for sediment reduction, it is necessary to do a research on the utilization of river sediment for brick raw materials. In this study, the utilization of sediment into bricks was proposed in the form of Unfired Bricks. Raw sediment material will be mixed with cement and sand with a certain composition to increase the compression strength of brick in order to meet one of the SNI requirements, i.e. 15-2094-2000 or SNI 03-0349-1989. Results found that the addition of cement and sand treatment can increase the compressive strength of the brick up to 44,176 kg/cm² at the age of 14 days. However, the compression strength test results are still below the compression strength of Red Brick requirements in accordance with SNI 15-2094-2000 where the minimum compression strength of brick is 50 kg /cm², but it qualify for the compression Strength Concrete Brick SNI 03-0349-1989 for the quality level of grade III with a minimum of 40 kg / cm² and grade IV with a minimum of 25 kg / cm²

Effects of Different Inflow Rate Patterns and Distributions of Grass Strips on Runoff and Sediment in an Engineering Accumulation Body

Engineering accumulation bodies are critical sources of artificial soil and water loss. The objectives of this study were to evaluate the effects of different inflow rate patterns and distributions of grass strips on runoff and sediment in engineering accumulation bodies. A field runoff plot (20 m long, 1 m wide, and 0.5 m deep) was used for inflow simulation experiments under four inflow rate patterns (even, rising, falling, and rising-falling) and five grass strip patterns (patterns Ⅰ-Ⅴ). The results showed that the changing trends of runoff rate and sediment yield increased with increasing inflow rate and decreased with reduction for the same grass strip pattern. Although the inflow rate pattern affected runoff and sediment yield, it had no significant effect on the total runoff and sediment. The influence of the grass strip pattern on runoff and sediment was significantly higher than that of the inflow rate pattern. The runoff reduction and sediment reduction effects of grass strip patterns were 12.23 to 49.62% and 12.92 to 80.54%, respectively. When grass strips were distributed on a slope in bands (pattern Ⅴ), the soil and water conservation effects were ideal, reducing the average runoff and sediment by 44.98% and 58.09%, respectively. Sediment reduction caused by decreasing runoff (SRR) was the main factor controlling erosion and sediment yield. This study can guide the configuration of vegetation control measures for soil and water loss in engineering accumulation bodies.

Seasonal variation in water and sediment fluxes of the Yangtze River under precipitation change and human interference

<p>Seasonal change of water and sediment fluxes is an important issue in flood/drought control and ecosystem protection. Based on trend analysis in dry and flood seasons during 1960–2014 at six major gauging stations on the Yangtze River, the largest river in China, significant homogenization of intra-year water discharge was found, while sharp decrease of sediment load in both seasons was tested. By reconstructing water and sediment series without the human interference, contributions of precipitation change, large dam constructions on the mainstream, and other human activities in each of the sub-basins of the Yangtze River were separated and quantified. It shows that precipitation change attributed for 9.5–23.6% to discharge homogenization in the middle and lower reaches of the Yangtze River, and increased sediment yield by 1.9–25.5% in both dry and flood seasons. Being the largest hydraulic project in the world, the Three Gorges Dam only explains 17.5–27.2% of the downstream homogenization in water flux, and 3.2–23.9% of sediment reduction in both seasons. Relatively small but massive human interference in the sub-basins was recognized as the primary factor, contributing over 60% to discharge homogenization and over 70% to seasonal sediment reduction, most notably in the Hanjiang sub-basin for water flux and in the Jianglingjiang sub-basin for sediment load.</p>

Changes of Flow and Sediment Transport in the Lower Min River in Southeastern China under the Impacts of Climate Variability and Human Activities

The Min River is the largest river in Fujian Province in southeastern China. The construction of a series of dams along the upper reaches of the Min River, especially the Shuikou Dam, which started filling in 1993, modified the flow processes at the lower Min River, leading to the significant increase in low-flows and slightly decrease in flood-flows. At the same time, reservoirs have more effects on the sediment transport process than flow process by trapping most sediment in the reservoirs, and greatly reduced the amount of sediment transporting downstream. Increase in vegetation cover also contributes to the decrease in sediment yield. The reduction in sediment together with excessive sand mining in the lower Min River resulted in the severe downward erosion of the riverbed. Using a reformulated elasticity approach to quantifying climatic and anthropogenic contributions to sediment changes, the relative contribution of precipitation variability and human activities to sediment reduction in the lower Min River are quantified, which shows that the sediment reduction is fully caused by human activities (including land use/land cover changes and dam construction).

Seasonal changes of sediment fluxes in the Yangtze River: roles of precipitation change, human conservation measures in sub-basins, and large dams

Seasonal sediment flux change is a key issue in riverbed evolution and flood control. This paper analyzed variations in sediment fluxes of the Yangtze River in dry and flood seasons during 1961–2014 and the impacts of precipitation change and human interference. Sediment fluxes in both dry and flood seasons decreased by 6.8–74.6 and 14.6–38.7%, respectively, based on daily sediment observations at six mainstream stations. However, precipitation increased sediment yields in both dry and flood seasons by 0.72–4.22 t/km2 (3.5–17.8%) and 4.95–73.32 t/km2 (1.9–25.5%), respectively, based on the reconstructed sediment series without anthropogenic interference. Therefore, sediment reduction due to human conservation measures and dam construction was up to 0.07–20.74 t/km2 (0.9–64.6%) in dry seasons and 27.47–85.35 t/km2 (6.5–23.7%) in flood seasons during 1980–2002, and further reduced 3.61–41.31 t/km2 (46.0–102.9%) in dry seasons and 175.63–471.52 t/km2 (59.6–126.2%) in flood seasons after the Three Gorges Reservoir (TGR) became operational in 2003. Contributions of human activities in six subregions to the reduction of the seaward sediment fluxes were calculated. Thereinto, the TGR only took up 3.2 and 23.9% in dry and flood seasons, respectively, which is below expectation.