| The change of suspended sediment in river is one of the results that change of regional climatic and surface cover pattern. On the one hand, it will cause the scour and silting evolution of the channel directly, which affect the normal function of the hydraulic projects, agricultural production, water resources distribution and channel management seriously. On the other hand, this change is also the signal of the developing trend on all kinds of environmental factors associated sediment producing and transporting.As a sample, Longchuanjiang river watershed, the main branch of Jinshajiang, is applied to research temporal and spatial changing regulation of the sediment flux based on hydraulic and physical geography theory and spatial information, distributed model and conventional statistical techniques. The relationship between climatic, surface cover pattern changing and sediment flux changing has been studied in this paper, main conclusions as follows:1. In the past decades of years, the temporal characteristic of the sediment transported are fit to the precipitation in Longchuangjiang River watershed. However, its changing trend characteristic is the result of land use pattern changed. The sediment amount and precipitation has a transparently ascending trend in 1970-1992, a descendant phenomenon appears in 2003-2008. The sediment amount has a transparently ascending abrupt changing in 1992, descending abrupt in 2002, which appears highly synchronous with the surface cover pattern changed.2. The relationship between surface cover pattern, soil eroded character changed and sediment transportation in river has been researched by interpreting 1974's, 1992's,2002's and 2007's satellite images in this paper. The results indicated that the cultivated land, woodland, grassland are main surface cover types in the watershed, which area ratio is 99.69% in 1974,99.13% in 1992,98.64% in 2002 and 96.75% in 2008. The most surface cover transferring has happened among the cultivated land, forest land, shrubbery since 1974. For example, the area of shrubbery and cultivated land has been subtracted 1901.3 km2 and 204.1 km2 respectively from 1974 to 1992, but the up-to-25 degree cultivated land added 24.3km2, meanwhile, the forest land area has been added 2094.4 km2. From 1992 to 2002, the area of cultivated land has been added 83.4km2, including the up-to-25 degree cultivated land added 23.4km2, at the same time, forest land area has been subtracted 730.1km2; the area of shrubbery and cultivated land has been subtracted 558.4km2 and 725.8km2 respectively from 2002 to 2008, including the up-to-25 degree cultivated land subtracted 82.5km, meanwhile, the forest land area has been added 1846km2.Soil eroded temporal character is well related with surface cover types changed, including the amount and the modulus of soil eroded changed. E.g.in 1974, the soil eroded amount was 2.31 X 107t, while 2.15 X 107t in 1992,2.84X 107t in 2002,2.11 X 107t in 2008. The soil eroded modulus was 2497t/(km2·a) in 1974,2331 t/(km2·a) in 1992,3077t/(km2·a) in 2002, in 2008, it was 2286t/(km2·a). The inner transformation of the same surface cover type has little effect to soil eroded character, but the transformation between different surface cover type has much effect to it, especially among the woodland, shrubbery and cultivated land. Woodland and shrubbery turned to cultivated land, especially to those up-to-25 degree cultivated land, the soil eroded intensity degree added 50%-70%, reversely, cultivated land, especially to those up-to-25 degree cultivated land, turned to woodland and shrubbery, the index subtracted much.Indirectly cause and effect relationship lies between the sediment transportation amount and surface cover pattern changed in Longchuangjiang River watershed. When the intensity of land use ascending, the sediment transportation amount is added, inversely, it is subtracted.3. The sediment transportation model build in this paper is used to modulate the sediment transportation process in Longchuangjiang River effectively, based on spatial information technology, soil erosion and hydrology theory. In the three phases of 1981-1987,1994-2000 and 2002-2008, the accuracy index R2 is 0.85?0.78 and 0.78;Nash-Sutclife efficiency index (Ens) is 0.71?0.65 and 0.69 respectively.4. The effect of climatic and surface cover pattern changed to sediment transported in river has a differentiation in several temporal phases. In 1977-1987, 1993-2000,2002-2008, climatic changed contributed about 44%,21.8% and 48.4% respectively.The effect of various surface cover type to sediment transportation amount raised in river are different. The capacity sequence of controlled sediment transportation in river as follows:forest land, shrubbery, up-to-25 degree cultivated land and non-up-to-25 degree cultivated land, grassland, sparse woodland. When the ratio of forest land area was 50%, whether its area added or subtracted, the sensitivity of sediment transportation in river was 91.55%, otherwise, when the ratio was 70%, the sensitivity was 70.71%, lower than 91.55%. As to cultivated land, the sensitivity of sediment transportation in river to up-to-25 degree cultivated land was higher about 8% than to non-up-to-25 degree cultivated land.5. The response of the sediment transportation amount in river to climatic and surface cover pattern changed in the future is different with the climatic and surface cover pattern changed extent, including theirs combination situation. The results as follows:(1) The sensitivity of sediment transportation amount raised up in river to precipitation increasing is very high, but the rainfall added up results in sediment transportation amount increased is much more than decreased by the rainfall subtracted the same ratio. Researching achievements indicated that rainfall added up average 20%, the increasing ratio of the sediment transportation amount in river will be 24.31%, inversely, and it will be 19.23% in August. And that, this effect in drought season is nearly neglected, but in rain season, this decreased or increased ration of sediment transportation amount in river is about 12%.(2) The response of sediment transportation amount in river of rain season to the forest land and shrubbery area subtraced is very sensitively. In 2020, the sediment transportation amount in river will rise up about 6%,8% respectively. But in 2030, the ratio is 8% and 10% respectively. At the same time, the added sum area of cultivated land will still result in the sediment transportation amount raised about 2% and 3%.(3) The effect of surface cover changed to sediment transportation amount in river in the future is increasing continuously in any of climatic changed scenario. The effect of rainfall subtracted to the sediment transportation amount decreased in river will be degraded gradually in whichever surface cover pattern; on the contrary, the effect of rainfall increased to the sediment transportation amount increased in river will be strengthened further. E.g. rainfall increases average 5% in August, if forest land area subtraced 10% and residential area added 100%, the increasing ratio of the -sediment transportation amount in river will be 13.21%, inversely, it will be 5.72%. In addition, even if the rainfall keeps stability, the movable soil eroded amount may be added in virtue of the land use explored drastically, it can result in the ratio of the sediment transportation amount in river increased about 3%.All the achiements made in this paper result in a more deep comprehension to water-sediment transportation regulation in Longchhuanjiang River. It not only applies a case and research direction to deep theoretical studied water-sediment transportation changing law and its affected factors in this watershed, but also provides theoretical basis and main struggle direction for soil erosion controlled, land use patterm and its function adjusted and realize the environment-society-economy system harmonious development in Longchuanjiang River watershed. |
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