Sediment Load Reduction Research Articles

Environmental assessment of soil erosion in Inabanga watershed (Bohol, Philippines)

Analysis of soil redistribution patterns in watershed areas provides information for understanding soil erosion and deposition for implementing management practices to improve agricultural land conditions and reduce sediment loads in river systems. This paper has demonstrated the use of Cesium-137 (137Cs) in estimating retrospective medium-term soil erosion rates in selected cassava cultivated areas in Pilar, a sub-watershed within the Inabanga watershed. To estimate erosion and deposition rates and elucidate the factors affecting the soil redistribution, samples were collected from a total of ninety-eight grid intersections representative of the local land use and slope gradients in the presence or absence of soil conservation practices. A proportional model was used to deduce soil redistribution rate estimates from 137Cs inventories measured from individual soil samples. Soil measurements of 137Cs activity-generated soil erosion rate gave values of 13.15 t ha−1 year−1 in cultivated areas practicing conservation measures and 22.23 t ha−1 year−1 in those with typical upland plantation, with the former corresponding to slight erosion case and the latter to moderate erosion case. The obtained values have provided an overview of the pattern of soil redistribution in the watershed area and reflect the impact of strategic soil erosion management being applied. Interestingly, in light of recent severe meteorological events befalling the region, e.g., super typhoon Haiyan and the 7.3 magnitude earthquake, the data obtained may serve as benchmark values for 137Cs activities against which changes in the soil movement and soil redistribution pattern along the watershed areas can be evaluated.

모델링 기법을 이용한 밭의 볏짚 지표피복의 부유사량 저감효과 평가 방법

Sediment-laden water leads to water quality degradation in streams; therefore, best management practices must be implemented in the source area to control nonpoint source pollution. Field monitoring was implemented to measure precipitation, direct runoff, and sediment concentrations at a control plot and straw-applied plot to examine the effect on sediment reduction in this study. A hydrology model, which employs Curve Number (CN) to estimate direct runoff and the Universal Soil Loss Equation to estimate soil loss, was selected. Twenty-five storm events from October 2010 to July 2012 were observed at the control plot, and 14 storm events from April 2011 to July 2011 at the straw-applied plot. CN was calibrated for direct runoff, and the Nash-Sutcliffe efficiency and coefficient of determination were 0.66 and 0.68 at the control plot. Direct runoff at the straw-applied plot was calibrated using the percentage direct runoff reduction. The estimated reduction in sediment load by direct runoff reduction calibration alone was acceptable. Therefore, direct runoff-sediment load behaviors in a hydrology model should be considered to estimate sediment load and the reduction thereof.

Impacts of Climate Variability and Human Activities on the Changes of Runoff and Sediment Load in a Catchment of the Loess Plateau, China

The objectives of this study are to investigate the changes of runoff and sediment load and their potential influencing factors in the Huangfuchuan catchment. The Mann-Kendall test and accumulative anomaly methods were, respectively, applied to examine the changing trends and abrupt changes. Both annual runoff and sediment load demonstrated significant reduction (p<0.05) with decreasing rates of −3.2 × 106 m3/a and −1.09 Mt/a, respectively. The abrupt changes were detected in 1979 and 1996 for the runoff and sediment load. All the runoff and sediment indices (runoff, sediment load, runoff coefficient, and sediment concentration) exhibited remarkable reduction (p<0.01). The climate variability contributed 24.4% and 25.1% during 1980–1996 and 1997–2010 to annual runoff decrease, respectively, and human activities accounted for the remaining 75.6% and 74.9%. In contrast, changes in precipitation accounted for 43.5% and 20.2% of sediment load reduction during 1980–1996 and 1997–2010, whereas the human activities contributed 56.5% and 79.8%, respectively. The relative contributions from climate variability and human activities to runoff and sediment load changes at annual scale were different from that at flood season scale. Results suggested the dominant role of soil and water conservations in the variation of runoff and sediment load in the catchment.

Using Fluvial Sediment Transport Equilibrium to Drive Stream Restoration and Establish Sediment Load Reduction Targets

Using Fluvial Sediment Transport Equilibrium to Drive Stream Restoration and Establish Sediment Load Reduction Targets

Sediment Transport Characteristic of the Ping River Basin, Thailand

This study examined the river sediment transport characteristics of the Ping River basin, which is one of the major river basins in Thailand. River surveys of the Ping River were carried out nine times between 2011 and 2013. Survey data included river cross sections, flow velocities, suspended sediment concentration, and bed load transport in the river. Analyzes of these data indicated that suspended transport rates in the Ping River during normal flow conditions in 2012-2013 ranged between 107 and 9,562 metric tons/day (mt/d), but increased to 35,300 mt/d during high flooding conditions (Thailand's Great Flood of 2011). The rate of bed load transport was 1,401 mt/d during the Flood of 2011. However, the measured bed load in 2012-2013 varied between 0 and 482 mt/d. The bed-to-suspended load ratio in the Ping River fluctuated in the broad range of 0-2.0. Estimates of total sediment transport in the Ping River were made using some of the classic equations from the hydrologic literature. The results obtained from the different methods show that the Laursen-Copeland formula gives the best estimate of total sediment transport rate of the Ping River compared to other methods. Results from this study also reveal that the Bhumibol Dam, constructed in 1964, has had a significant effect on suspended sediment load reduction downstream of the dam.

Reduced sediment transport in the Yellow River due to anthropogenic changes

The erosion, transport and redeposition of sediments shape the Earth's surface, and affect the structure and function of ecosystems and society(1,2). The Yellow River was once the world's largest carrier of fluvial sediment, but its sediment load has decreased by approximately 90% over the past 60 years(3). The decline in sediment load is due to changes in water discharge and sediment concentration, which are both influenced by regional climate change and human activities. Here we use an attribution approach to analyse 60 years of runoff and sediment load observations from the traverse of the Yellow River over China's Loess Plateau - the source of nearly 90% of its sediment load. We find that landscape engineering, terracing and the construction of check dams and reservoirs were the primary factors driving reduction in sediment load from the 1970s to 1990s, but large-scale vegetation restoration projects have also reduced soil erosion from the 1990s onwards. We suggest that, as the ability of existing dams and reservoirs to trap sediments declines in the future, erosion rates on the Loess Plateau will increasingly control the Yellow River's sediment load.

Temporal Variations of Flow–sediment Relationships in a Highly Erodible Catchment of the Loess Plateau, China

AbstractThe flow–sediment relationship is important to understand the soil erosion and land degradation processes in severe eroded areas. This study researches on variations of streamflow, sediment load, and flow–sediment relationship on multi‐temporal scales (annual, flood season and, monthly scales) in a highly erodible catchment of Chinese Loess Plateau. The results demonstrated that the streamflow, sediment load, sediment concentration, runoff coefficient, and sediment coefficient all experienced evident reductions, and the decrease in the middle and downstream stations was more significant compared with the upstream stations. The land use changes and implementation of soil and water conservation measures played major role for the streamflow and sediment load reductions with respect to precipitation change, and the runoff coefficient and sediment coefficient linearly decreased with the percentage of conservation measure area. The runoff‐sediment yield relationship on annual, flood season, and monthly scales could be generally characterized by the linear function, and the slopes during the post‐change period was lower than those during the pre‐change period of sediment load. The sediment concentration–streamflow discharge relationship represented consistent form over the entire study period, and the logarithmic function was appropriate to describe the relationships on the three timescales. The decrease of sediment concentration contributed greatest (60·7%) to sediment reduction compared with runoff productivity of rainfall (30·2%) and precipitation (9·1%). Copyright © 2015 John Wiley & Sons, Ltd.

Sediment transport in two mediterranean regulated rivers

Mediterranean climate is characterized by highly irregular rainfall patterns with marked differences between wet and dry seasons which lead to highly variable hydrological fluvial regimes. As a result, and in order to ensure water availability and reduce its temporal variability, a high number of large dams were built during the 20th century (more than 3500 located in Mediterranean rivers). Dams modify the flow regime but also interrupt the continuity of sediment transfer along the river network, thereby changing its functioning as an ecosystem. Within this context, the present paper aims to assess the suspended sediment loads and dynamics of two climatically contrasting Mediterranean regulated rivers (i.e. the Ésera and Siurana) during a 2-yr period. Key findings indicate that floods were responsible for 92% of the total suspended sediment load in the River Siurana, while this percentage falls to 70% for the Ésera, indicating the importance of baseflows on sediment transport in this river. This fact is related to the high sediment availability, with the Ésera acting as a non-supply-limited catchment due to the high productivity of the sources (i.e. badlands). In contrast, the Siurana can be considered a supply-limited system due to its low geomorphic activity and reduced sediment availability, with suspended sediment concentration remaining low even for high magnitude flood events. Reservoirs in both rivers reduce sediment load up to 90%, although total runoff is only reduced in the case of the River Ésera. A remarkable fact is the change of the hydrological character of the River Ésera downstream for the dam, shifting from a humid mountainous river regime to a quasi-invariable pattern, whereas the Siurana experiences the opposite effect, changing from a flashy Mediterranean river to a more constant flow regime below the dam.

Prioritising catchment rehabilitation for multi objective management: An application from SE-Queensland, Australia

Freshwater ecosystems are among the most diverse environments on Earth but also one of the most degraded and threatened due mainly to the intense human modification and exploitation. Despite the increase in funds devoted to rehabilitation of these systems little success has been reported so far. When planning for rehabilitation of catchments, stakeholders have to decide what combination of actions to implement and at which locations from a vast number of possible options. Often these activities are constrained by limited budgets. Here we apply the principles of systematic planning to rehabilitation, integrating erosion, sediment transport, ecological and economic objectives into the planning process to enhance the effectiveness of the rehabilitation plans and to support stakeholders in better understanding the effects of various objectives. We develop and apply a multi-objective approach to find a set of near-optimal trade-off solutions among a large number of candidate combinations of rehabilitation actions under sometimes competing objectives. We use a Pareto-optimal approach to store potentially useful combinations of rehabilitation actions (trade-offs) along the management objective gradients. Presenting those trade-offs as a function of the management objectives allow users to understand the commonalities and differences of various rehabilitation options when selecting different objectives. It is the learning from these relationships that classic optimisation approaches often lack.As proof of concept, we used an example rehabilitation project in South East Queensland (Australia) that aims to reduce sediment loads and improve the ecological health (measured as the EHMP index) of rivers while minimizing opportunity cost of rehabilitation plans. Opportunity cost is defined as the forgone economic value that would be compromised by the implementation of a rehabilitation plan. We found that our approach was efficient and effective in finding and systematically presenting promising trade-offs along different objective gradients (sediment reduction, ecosystem health and opportunity cost economics).

Multi‐temporal scale changes of streamflow and sediment load in a loess hilly watershed of China

AbstractGlobal climate change and diverse human activities have resulted in distinct temporal–spatial variability of watershed hydrological regimes, especially in water‐limited areas. This study presented a comprehensive investigation of streamflow and sediment load changes on multi‐temporal scales (annual, flood season, monthly and daily scales) during 1952–2011 in the Yanhe watershed, Loess Plateau. The results indicated that the decreasing trend of precipitation and increasing trend of potential evapotranspiration and aridity index were not significant. Significant decreasing trends (p < 0.01) were detected for both the annual and flood season streamflow, sediment load, sediment concentration and sediment coefficient. The runoff coefficient exhibited a significantly negative trend (p < 0.01) on the flood season scale, whereas the decreasing trend on the annual scale was not significant. The streamflow and sediment load during July–August contributed 46.7% and 86.2% to the annual total, respectively. The maximum daily streamflow and sediment load had the median occurrence date of July 31, and they accounted for 9.7% and 29.2% of the annual total, respectively. All of these monthly and daily hydrological characteristics exhibited remarkable decreasing trends (p < 0.01). However, the contribution of the maximum daily streamflow to the annual total progressively decreased (−0.07% year−1), while that of maximum daily sediment load increased over the last 60 years (0.08% year−1). The transfer of sloping cropland for afforestation and construction of check‐dams represented the dominant causes of streamflow and sediment load reductions, which also made the sediment grain finer. Copyright © 2015 John Wiley & Sons, Ltd.

Quantifying the anthropogenic and climatic contributions to changes in water discharge and sediment load into the sea: A case study of the Yangtze River, China

Based on data from the Datong hydrological station and 147 meteorological stations, the influences of climate change and human activities on temporal changes in water discharge and sediment load were examined in the Yangtze River basin from 1953 to 2010. The Mann–Kendall test, abrupt change test (Mann–Kendall and cumulative anomaly test), and Morlet wavelet method were employed to analyze the water discharge and sediment load data measured at the Datong hydrological station. The results indicated that the annual mean precipitation and water discharge exhibited decreasing trends of −0.0064mm/10yr and −1.41×108m3/yr, respectively, and that the water sediment load showed a significant decreasing trend of −46.5×106t/yr. Meanwhile, an abrupt change in the water discharge occurred in 2003. The sediment load also exhibited an abrupt change in 1985. From 1970 to 2010, the climate change and human activities contributed 72% and 28%, respectively, to the water discharge reduction. The human-induced decrease in the sediment load was 914.03×106t/yr during the 1970s and 3301.79×106t/yr during the 2000s. The contribution from human activities also increased from 71% to 92%, especially in the 1990s, when the value increased to 92%. Climate change and human activities contributed 14% and 86%, respectively, to the sediment load reduction. Inter-annual variations in water discharge and sediment load were affected by climate oscillations and human activities. The effect of human activities on the sediment load was considerably greater than those on water discharge in the Yangtze River basin.

Spatio-temporal characteristics and causes of changes in erosion-accretion in the Yangtze (Changjiang) submerged delta from 1982 to 2010

The Yangtze delta’s response to accelerating river damming and irrigation is a topic of global concern. This research analyzed the general erosion-accretion of the submerged delta front, the spatio-temporal changing pattern in different sub-regions, the geomorphological changes in typical cross-sections, and the geomorphological causes of the four main sub-regions (the eastern tidal wetland of Chongming-CM, the Hengsha shoal-HS, the Jiuduansha wetland-JDS, and the eastern tidal wetland of Nanhui-NH). Data sources include topographic data measured at high-resolution, sediment load at Datong Station, and the corresponding estuary construction information. Major findings are: (1) in general, the study area had slightly eroded (the erosion area ratio was 51.83% and the accretion area ratio was 48.17%) from 1982 to 2010, and it had experienced a shift of “erosion-accretion-erosion”. The spatio-temporal change of geomorphology was also significant in the eight sub-regions, excluding constant erosion in the North Channel; (2) evolution in eastern and northern CM and HS, northern JDS, and the region within the 5 m isobath of NH was dominated by vertical deposition, which was the opposite of that in southern CM and HS, and the region within the 5 m isobath of eastern and southern JDS; (3) on the whole, the encompassed surface areas (ESAs) of the 2 m and 5 m isobaths kept increasing, and the annual growth rates reached 10.42 km2/yr and 7.99 km2/yr respectively during 1982–2010 (however, four sub-regions exhibited disagreements), and in the whole region and all sub-regions, the ESA of the 10 m isobath decreased, while the ESA of the 15 m isobath changed slightly during the period and remained stable; (4) being less influenced by the estuarine engineering, CM was the only sub-region where the ESA of the isobath decreased in accordance with the decline of the sediment load. Major conclusions are that estuarine engineering projects play an increasingly important role in affecting the submerged delta against the macro-background of the reduction of sediment load, the change of ESA and the distribution of isobaths. Along with the accelerating construction of the Shanghai International Shipping Centre and reclamation project, the geomorphological evolution of the submerged delta will become more complex and thus deserves frequent monitoring in the future.

Identifying priority sites for low impact development (LID) in a mixed-use watershed

Low impact development (LID), a comprehensive land use planning and design approach with the goal of mitigating land development impacts to the environment, is increasingly being touted as an effective approach to lessen runoff and pollutant loadings to streams. Broad-scale approaches for siting LID have been developed for agricultural watersheds, but are rare for urban watersheds, largely due to greater land use complexity. Here, we introduce a spatially-explicit approach to assist landscape architects, urban planners, and water managers in identifying priority sites for LID based exclusively on freely available data. We use a large, mixed-use watershed in central Oklahoma, the United States of America, as a case-study to demonstrate our approach. Our results indicate that for one sub-catchment of the Lake Thunderbird Watershed, LID placed in 11 priority locations can facilitate reductions in nutrient and sediment loading to receiving waters by as much as 16% and 17%, respectively. We had a high rate of correctly identified sites (94±5.7%). Our systematic and transferable approach for prioritizing LID sites has the potential to facilitate effective implementation of LID to lessen the effects of urban land use on stream ecosystems.

Effect of replacing surface inlets with blind or gravel inlets on sediment and phosphorus subsurface drainage losses.

Open surface inlets that connect to subsurface tile drainage systems provide a direct pathway for movement of sediment, nutrients, and agrochemicals to surface waters. This study was conducted to determine the reduction in drainage effluent total suspended sediment (TSS) and phosphorus (P) concentrations and loads when open surface inlets were replaced with blind (in gravel capped with 30 cm of soil) or gravel (in very coarse sand/fine gravel) inlets. In Indiana, a pair of closed depressions in adjacent fields was fitted with open inlet tile risers and blind inlets in 2005 and monitored for flow and water chemistry. Paired comparisons on a storm event basis during the growing season for years 2006 to 2013 showed that TSS loads were 40.4 and 14.4 kg ha event for tile risers and blind inlets, respectively. Total P (TP) and soluble reactive P (SRP) loads were 66 and 50% less for the blind inlets, respectively. In Minnesota, TSS and SRP concentrations were monitored for 3 yr before and after modification of 24 open inlets to gravel inlets in an unreplicated large-field on-farm study. Median TSS concentrations were 97 and 8.3 mg L and median SRP concentrations were 0.099 and 0.064 mg L for the open inlet and gravel inlet periods, respectively. Median TSS and SRP concentrations were elevated for snowmelt vs. non-snowmelt seasons for open and gravel inlets. Both replacement designs reduced suspended sediment and P concentrations and loads. The Indiana study suggests blind inlets will be effective beyond a 10-yr service life.

Erratum to: Impacts of human activities on the evolution of estuarine wetland in the Yangtze Delta from 2000 to 2010

The wetland in the Yangtze Delta plays an important role in coastal protection against erosion, water purification, and habitat maintenance of migratory birds. The Yangtze Delta is one of the largest economic zones (e.g., Shanghai) in China. Human activities severely affect wetland evolution. Wetland mapping was performed from multi-temporal remote sensing data of Landsat during the period 2000–2010 at intervals of about 5 years, and spatiotemporal changes in wetland characteristics as well as driving forces for such changes were analyzed. Results indicated the Yangtze River estuarine wetland area experienced a net increase of 63 % during the period of 2000–2010; from 2005 onwards, however, the rate of increase has decreased. Human activities, including upstream dam construction, estuarine engineering, land reclamation, and ecological engineering, played an important role in wetland evolution during this short period. Reduction of riverine sediment loads led to decreases in the increase rate of estuary wetland; 95 % of the estuarine shoreline is embanked by seawalls, which exerts negative effects because closure promotes substantial degradation of wetland areas. Urbanization and expansion of Shanghai facilitated regular land reclamation of wetland and led to 35 % wetland loss. Intentional artificial planting of aquatic plants and groyne construction accelerated sediment deposition and wetland formation to compensate for coastal wetland loss.

Using SWAT to determine reference nutrient conditions for small and large streams

Developing reference criteria for nutrient conditions on streams can be difficult especially in heavily farmed or urbanized regions where most of the landscape has been impacted by human development. SWAT (soil water assessment tool) simulations permit the removal of the anthropogenic impacted land use, allowing the simulation of natural conditions and a prediction of reference conditions. A Genesee River watershed simulation was developed to determine the nutrient and sediment contributions of subbasins of the Genesee River under the current human-impacted conditions and contrasted against natural conditions. Nutrient boundary values estimated for Genesee basin small wadeable streams (34.3μgP/L) were nearly identical to those calculated by others for small, wadeable streams (30.7μgP/L). For large streams, the simulation-based boundary total phosphorus (TP) value (75.8μgP/L) of the Genesee River was high compared to other observations in New York State (30μgP/L). Causes in the variability in large stream reference values include inappropriate use of regional reference conditions, stream bank erosion, basin geology, soil type, and catchment area. When river bank stabilization was added to the simulation, a 34.3% reduction in phosphorus loading was observed, resulting in a boundary value of ~54μgP/L. This reduction in the simulated sediment load suggested that the Genesee River has a higher natural sediment and TP load than most streams in NYS. SWAT is an effective tool for simulations of small streams and may be an effective method in determining reference conditions for large rivers.

Natural and anthropogenic controls over suspended sediments within a mountainous Appalachian watershed: implications for watershed restoration

The upper Elk River (620 km2), located in mountainous east-central West Virginia, is one of the premier cold-water fisheries in the eastern United States. However, sediment run-off from both forestry and non-forestry-related disturbance has the potential to threaten the quality of wild trout populations. General linear models were used to link spatial and temporal variation in total suspended solid (TSS) concentrations throughout the watershed to natural (i.e. landform and geology) and anthropogenic (forest management practices, other land-use disturbance [residential and commercial development, agriculture, and recreation], census roads) landscape attributes. In addition, through a unique paired sampling design, we tested the hypothesis that increasing levels of disturbance (i.e. forest management and other land use activities) within a watershed would result in a proportional increase in TSS concentrations. Spatial variation in TSS concentration was found to primarily be explained by land-use disturbance (partial R2 = 0.66) and secondarily by forest management practices (R2 = 0.13) and road area (R2 = 0.08). Results of a paired sampling design further indicated that significant increases in TSS concentrations were the result of intense land-use disturbance associated with activities other than forest management. Temporal variability (i.e. CV) in TSS was primarily related to dry flat area (partial R2 = 0.28) and percent calcareous bedrock (R2 = 0.21), suggesting natural sedimentation processes associated with karst geologies may exacerbate effects of anthropogenic disturbance. These results suggest that forestry-related best management practices being used in this mountainous region were effective in reducing sediment loads to nearby waterbodies, and improved management of non-forestry disturbance may be needed to protect this valuable fishery from sediment-related impacts.

生态恢复对流域水沙演变趋势的影响及其程度分析——以北洛河上游为例

The Loess Plateau in China is characterized by a heavily dissected landscape and severe soil erosion. To fully understand the impacts of soil conservation measures and vegetation restoration on streamflow,sediment load and runoffsediment behaviors,hydrologic data over 47 years(1963 to 2009) in the upper reaches of the Beiluo River( drainage area of 3408 km2) are assessed. The Beiluo is a secondary tributary of the Yellow River,and has had substantial vegetation restorative effects on the Loess Plateau. Based on the Mann-Kendall trend test,Pettit statistical test and flow duration curve(FDC),the daily streamflow and sediment load at Wuqi hydrological station,which is the maximum control station in theupper reaches of the Beiluo River,was chosen to investigate temporal change and evolution characteristics. Precipitation data and rainfall erosion force were interpolated using tessellation polygons from five representative meteorological stations on the Loess Plateau. A dual mass curve and empirically- based hydrological modeling method were also used to estimate the response of streamflow and sediment load to climate change and human activities. The results indicate that:(1) In the past50 years,under a background of precipitation with no significant trend,both streamflow and sediment load had significant negative trends( P 0. 01),with average annual rates of- 0. 28 mm km- 2a- 1and- 180 t km- 2a- 1,respectively. Under the influence of soil conservation measures that have been applied on the Loess Plateau since the 1960 s,there were change points in 1979 and 2002. Thus,the entire study period was divided into a period 1 of base(1963—1979),period 2 of comprehensive harness of soil and water conservation(1980—2002),and period 3 of the Grain for Green project(2003—2009).(2) The FDC showed that,compared with period 1,streamflow in period 2 for 5% and 50% decreased by 17. 0%and 5. 2%,respectively,while it increased by 94. 2% for 95%. Suspended sediment load decreased more significantly,with 34. 6% and 40. 1% for 5% and 50%,respectively,and no suspended sediment days remained almost constant for95%. Period 3 saw more remarkable changes in both streamflow and suspended sediment load. For 5% and 50%,streamflow decreased by 40. 2% and 26. 8%,respectively,while suspended sediment load decreased by 95. 7% and 96.8%,respectively. For 95%,streamflow rose by 128. 1%,and no sediment days increased. The reduction of sediment load was greater than that of streamflow,with the periods altered and negative changes of sediment load.( 3) Compared with period 1,streamflow and sediment load decreased by 0. 10 × 108m3(3 mm) and 0. 04 × 108t(1408 t km- 2a- 1) in period2. It was estimated that human activities accounted for 38. 2% and 51. 4% of the changes of streamflow and sediment load,respectively. In period 3,there was a greater reduction in both streamflow and sediment load,with 0. 52 × 108m3(15. 2mm) and 0. 33 × 108t(9683. 1t km- 2a- 1),respectively,with effects reaching 74. 7% and 86. 7%. Great improvement in the ecological environment of the Loess Plateau has already demonstrated the advantages of biological treatments on a regional scale in reducing flood volumes,and compensating streamflow.

Co-evolution of soil and water conservation policy and human–environment linkages in the Yellow River Basin since 1949

Policy plays a very important role in natural resource management as it lays out a government framework for guiding long-term decisions, and evolves in light of the interactions between human and environment. This paper focuses on soil and water conservation (SWC) policy in the Yellow River Basin (YRB), China. The problems, rural poverty, severe soil erosion, great sediment loads and high flood risks, are analyzed over the period of 1949–present using the Driving force–Pressure–State–Impact–Response (DPSIR) framework as a way to organize analysis of the evolution of SWC policy. Three stages are identified in which SWC policy interacts differently with institutional, financial and technology support. In Stage 1 (1949–1979), SWC policy focused on rural development in eroded areas and on reducing sediment loads. Local farmers were mainly responsible for SWC. The aim of Stage 2 (1980–1990) was the overall development of rural industry and SWC. A more integrated management perspective was implemented taking a small watershed as a geographic interactional unit. This approach greatly improved the efficiency of SWC activities. In Stage 3 (1991 till now), SWC has been treated as the main measure for natural resource conservation, environmental protection, disaster mitigation and agriculture development. Prevention of new degradation became a priority. The government began to be responsible for SWC, using administrative, legal and financial approaches and various technologies that made large-scale SWC engineering possible. Over the historical period considered, with the implementation of the various SWC policies, the rural economic and ecological system improved continuously while the sediment load and flood risk decreased dramatically. The findings assist in providing a historical perspective that could inform more rational, scientific and effective natural resource management going forward.

Functions of Chisan dams in large-scale granular mass-flow experiments on Sakurajima volcano pumiceous clasts

We investigated the fundamental behaviour of Chisan (check) dams in response to the presence or absence of impounded sediment with different levels of saturation. Large-scale model flume experiments were conducted by use of a model Chisan dam that had been backfilled with pumiceous clasts taken from the Sakurajima volcano in Kagoshima prefecture, Japan. In these experiments, the miniature dam was situated midway down the flume under different backfill sediment conditions and the basal pore-fluid pressure, normal flow depth, and impact load of the granular mass were carefully monitored. Saturated sediment with a volume of 0.6 m3 was released along the slope of the flume segment at 30° and excess pore-fluid pressure was generated, corresponding to a sediment velocity of approximately 4.8 m s−1. Direct collision of the sediment with the Chisan dam meant the peak impact loads of granular mass against the back surface of the dam exceeded 157 N in experiments without backfill sediment but were as low as 32.1 N in experiments with sediment. Accordingly, placing the backfill sediment substantially reduced peak impact loads. The sediment captured by the Chisan dams was also calculated. For experiments using saturated backfill sediment, the dam captured only 35 % of the material, indicating that most of the granular mass passed over the dam. However, in experiments without backfill sediment or with unsaturated backfill sediment, over 90 % was captured. Although Chisan dams with unsaturated backfill sediment lacked pocket space, almost equivalent granular masses were trapped in these experiments. On the basis of these results, we suggest that Chisan dams with unsaturated backfill sediment could effectively counter debris flow, reducing sediment loads along the streams draining Sakurajima volcano.