Siltation

About: Siltation is a(n) research topic. Over the lifetime, 1420 publication(s) have been published within this topic receiving 20983 citation(s).

The political economy of soil erosion in developing countries

Abstract: Argues for combining the study of physical and social processes to study the political economy of soil erosion; the study must include a 'place-based' analysis of soil erosion, where it actually occurs, where flooding and siltation caused by soil erosion in one place affects another, and where land users have been spatially displaced to and from areas. It must also include 'non-place- based' analysis of the relations of production under which land is used including land tenure, rents, prices of agricultural inputs and outputs. Bringing these two analyses together, a 'bottom-up' approach is outlined in which the focus is first directed to the smallest unit of decision making in the use of land, the family and the household, up to the government and administration. At the latter level, it looks at where power lies and how it is used.

Soil Erosion Impact on Agronomic Productivity and Environment Quality

Abstract: Soil erosion is a global issue because of its severe adverse economic and environmental impacts. Economic impacts on productivity may be due to direct effects on crops/plants on-site and off-site, and environmental consequences are primarily off-site due either to pollution of natural waters or adverse effects on air quality due to dust and emissions of radiatively active gases. Off-site economic effects of erosion are related to the damage to civil structure, siltation of water ways and reservoirs, and additional costs involved in water treatment. There are numerous reports regarding the on-site effects of erosion on productivity. However, a vast majority of these are from the U.S., Canada, Australia, and Europe, and only a few from soils of the tropics and subtropics. On-site effects of erosion on agronomic productivity are assessed with a wide range of methods, which can be broadly grouped into three categories: agronomic/soil quality evaluation, economic assessment, and knowledge surveys. Agronomic me...

Effect of siltation on stream fish communities

Abstract: The effect of siltation on stream fish in northeast Missouri was evaluated using community structural measurements and a functional approach that emphasized feeding and reproductive guilds. As the percentage of fine substrate increased, the distinction among riffle, run, and pool communities decreased, primarily because the number of individuals of typical riffle species decreased. Within the riffle communities the abundance of fish of two feeding guilds — benthic insectivores and herbivores — was reduced as the percent of fine substrate increased. The abundance of fish in other feeding guilds was not affected. The only reproductive guild to be similarly affected was the simple and lithophilous, whose members require a clean gravel substrate for spawning. Species within each guild affected by siltation had significantly similar trends in abundance. The guild analysis indicated that species with similar ecological requirements had a common response to habitat degradation by siltation.

Yangtze River of China: historical analysis of discharge variability and sediment flux

Abstract: Hydrological records (covering a 100-year period) from the upper, middle and lower Yangtze River were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin. The Yangtze discharge, as expected, increases from the upper drainage basin downstream. Only an estimated 50% of the discharge is derived from the upper Yangtze, with the rest being derived from the numerous tributaries of the middle and lower course. However, the distribution of sediment load along the Yangtze is the reverse of that observed for discharge, with most of the sediment being derived from the upper basin. A dramatic reduction in sediment load (by ∼0.8×108 tons/year) occurs in the middle Yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper Yangtze rock sections. Considerable siltation also occurs in the middle Yangtze drainage basin as the river cuts through a large interior Dongting Lake system. Sediment load in the lower Yangtze, while significantly less than that of the upper river, is somewhat higher than the middle Yangtze because of additional load contributed by adjacent tributaries. A strong correlation exists between the discharge and sediment load along the Yangtze drainage basin during the dry season as lower flows carry lower sediment concentration. During the wet season, a strong correlation is also present in the upper Yangtze owing to the high flow velocity that suspends sand on the bed. However, a negative to poor correlation occurs in the middle and lower Yangtze because the flow velocity in these reaches is unable to keep sand in suspension, transporting only fine-grained particles downstream. Hydrological data are treated for 30 years (1950–1980), when numerous dams were constructed in the upper Yangtze drainage basin. At Yichang and Hankou hydrological stations, records revealed a decreasing trend in annual sediment load, along with slightly reduced annual discharge at the same stations. This can be interpreted as the result of water diversion primarily for agriculture. Sediment load at Datong further downstream is quite stable, and not influenced by slightly reduced discharge. Furthermore, sediment concentration at the three hydrological stations increased, which can be attributed to sediment loss in association with intensifying human activity, especially in the upper drainage basin, such as deforestation and construction of numerous dams. Mean monthly sediment load of these 30 years pulses about 2 months behind discharge, implying dam-released sediment transport along the entire river basin during the high water stage.

Human impact on floods and flood disasters on the Yangtze River

Abstract: In the middle reaches of the Yangtze River, the floods have become more and more frequent, and the water level rises higher than before. The damages are becoming ever more serious. This is primarily a consequence of human activity in the river basin. Three aspects deserve particular attention. First, destruction of vegetation has led to soil erosion in the upper reaches. In the past 30 years, the forest cover has been reduced to half, while the area exposed to severe erosion doubled in size. In the long run, this can be expected to increase flooding. Second, land reclamation and siltation has reduced lake sizes. This has resulted in decrease of the flood storage capacity. Third, the construction of levees has caused flood levels to rise due to restricted flood discharge capacity. Establishment of the Great Jinjiang levee caused silting up of the riverbed and valley in the mid-reaches of Yangtze. Consequently, the discharge capacity decreased to 60,000–68,000 m 3 /s, which is sufficient only for ordinary floods. This article concludes that the deteriorating flood situation is the result of inappropriate human intervention in the natural environment. It is suggested that the appropriate strategy should change from “keeping the flood away” to “giving the flood way”. Related tactics and strategies under consideration are briefly summarized.