金沙江支流龙川江流域河流输沙特征及其对气候和地表覆被变化的响应

【作者】 曾和平；

【导师】 周跃；

【作者基本信息】 昆明理工大学 ， 环境工程， 2009， 博士

【摘要】 河流输沙变化是流域气候与地表覆被格局变化的结果之一,一方面会导致河道的冲淤过程随之发生改变,对所处流域的水利工程、农业生产、水资源分配和河道管理带来影响；同时也表征着与流域产输沙有密切关联的各种环境要素改变的趋势。论文以自然地理学和水文动力学为理论基础,集成空间信息技术、建模以及数学分析方法,探讨了河流输沙过程与气候和地表覆被变化之间的相互影响及其关系,主要结论有：1、河流输沙的时间序列特征与流域降雨的时序特征基本一致,而趋势性特征由地表覆被变化决定。输沙和降雨量在1970-2002年间波动上升,2003-2008年间下降。河流输沙与降雨受强降雨事件的影响不明显。输沙量在1992和2002年出现的增加与减少跃变,与地表覆被变化高度一致。2、以1974、1992、2002和2007年的卫星影像为数据源,研究了流域地表覆被、土壤侵蚀特性以及河流输沙与地表覆被变化的相互关系。地表覆被以有林地、耕地和灌木林地为主,其中1974年占99.69%,1992年占99.13%,2002年占98.64%,2008年占96.75%。地表覆被类型间的转移主要发生在有林地、灌木林地、耕地之间,如1974-1992年,灌木林地减少了1901.3km2,耕地总量减少了204.1km2,但陡坡耕地增加了24.3 km2,有林地则增加了2094.4km2；1992-2002年,耕地增加了83.4km2,其中陡坡耕地增加了23.4 km2,有林地则减少了730.1km2；2002-2008年,灌木林地减少了558.4km2,耕地减少了725.8km2,其中陡坡耕地减少了82.5km2,有林地则增加了1846km2。土壤侵蚀变化的时间特性与地表覆被变化有很好的关联,表现为土壤侵蚀量和土壤侵蚀模数与地表覆被变化趋势的一致性,如土壤侵蚀量在1974年为2.31×107t,1992年为2.15×107t,2002年为2.84×107t,2008年为2.11×107t；侵蚀模数在1974年为2497t/(km2·a),1992年为2331t/(km2·a),2002年为3077 t/(km2·a),2008年为2286 t/(km2·a)。流域内各地表覆被类型内部的转化对土壤侵蚀特性的影响不大,地表覆被类型间的转化以有林地、灌木林地和耕地间相互转换对土壤侵蚀特性影响最大。有林地、灌木林地变为耕地,尤其是陡坡耕地,侵蚀强度会增加50-70%,而耕地,尤其是坡耕地向有林地、灌木林地的变化,会大大降低土壤侵蚀强度。河流输沙变化与地表覆被变化之间是间接的因果关系。1974-2002年,地表覆被向使土壤侵蚀强度增加的方向转化,河流输沙量呈增加趋势；2002-2008年,地表覆被向使土壤侵蚀强度降低的方向转化时,河流输沙量即呈减少趋势。3、应用空间信息技术、土壤侵蚀和水文动力学理论建立河流输沙模型对龙川江流域的河流输沙过程进行了有效地模拟。1981-1987、1994-2000和2002-2008年三个时段的模拟精度R2分别为0.85、0.78、0.78；Nash-Sutclife效率(Ens)分别为0.71、0.65和0.69。4、气候和地表覆被变化对河流输沙变化的影响,在不同时段有差别。气候变化在1977-1987、1993-2000、2002-2008年时段对河流输沙量的贡献率分别为44%、21.8%和48.4%。不同地表覆被类型对河流输沙的影响不同。控制河流输沙强度的顺序表现为有林地>灌木林地>陡坡耕地>非陡坡耕地>草地>疏林地。其中,有林地在1993-2000间的面积比例为50%左右时,其增减对河流输沙变化的敏感性最为突出,达到了91.55%,而当其面积比例在2008年为70%左右时,对河流输沙变化的敏感性反而最低,为70.71%；河流输沙对陡坡耕地增减的敏感性要高于非陡坡耕地约8个百分点。5、河流输沙对未来气候和地表覆被情景的响应,随气候、地表覆被变化程度及其组合状况呈现出不同的特点：(1)河流输沙对气候要素变化的响应,主要表现为降雨量的增减对河流输沙量增减的显著影响。降雨增加引起的河流输沙增加幅度,比降雨减少相同幅度引起的河流输沙减少幅度大。以1974-1987年的数据平均值为参照,如8月份降雨增加20%,输沙会增加24.31%,降雨减少20%,输沙则只减少19.23%。降雨量在干季的增减引起的河流输沙量变化平均值小于0.5%；在雨季的增减引起的河流输沙量变化平均值为12%左右；(2)河流雨季输沙对未来地表覆被变化中有林地和灌木林地面积减少的响应十分敏感。以2002-2008年的数据平均值为参照,2020年雨季河流输沙约各增加6%和8%,2030年约各增加8%和10%；耕地总面积的增加,仍然导致河流雨季输沙2020年增加约2%,2030年增加约3%；(3)地表覆被变化在各种气候情景下对河流输沙的影响呈一直增加的趋势。以2002-2008年的数据平均值为参照,与单一气候变化对输沙的影响相比,未来地表覆被情景下,降雨量减少对输沙减少的影响呈衰减态势,而降雨增加对输沙的影响则进一步强化。以雨季8月的河流输沙为例,当有林地减少10%,建设用地增加100%的情景下,降雨增加5%,将导致河流输沙增加13.21%；而降雨减少5%,则引起河流输沙减少5.72%；在降雨量不发生变化的情况下,土地利用强度的增加,也使河流输沙平均增加3%左右。本文的上述研究成果,加深了对龙川江流域水沙过程规律的理解与认识,不仅为在本区域更深入进行河流水沙变化及其影响的理论研究提供案例支持和方向,也为在本流域进行土壤侵蚀治理、调整土地利用结构和功能,实现区域生态环境-社会经济系统协调发展提供了理论依据和主攻方向,具有积极的现实意义。更多还原

【Abstract】 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.更多还原