黄土坡面产流产沙过程及微地形变化特征

坡面土壤侵蚀过程不仅可以通过坡面的产流产沙过程反映,还可以通过降雨过程中坡面微地形变化特征来反映。对9°、12°、15°、20°、25°坡度下面积较小坡面模拟降雨,获取降雨过程中径流泥沙数据及降雨前后坡面微地形变化数据。结果显示：（1）初始产流时间随着坡度的增加先增加后减小,且初始产流时间较长;（2）15°、20°时的产流率不稳定,18 min后产沙率规则性波动起伏;（3）随着坡度的增大,降雨过程后坡面比表面积值随着坡度的增大而增大,坡面的高程变异系数都有所增大。     

黄土坡面汇沙对细沟侵蚀的影响与贡献

细沟侵蚀是黄土高原坡面极其重要的侵蚀过程之一,汇沙对细沟侵蚀强弱具有重要影响,阐明汇沙对细沟侵蚀的影响与贡献,可以揭示坡面细沟侵蚀过程机理,并为治理坡面水土流失提供科学依据.采用定流量人工放水的组合小区模拟降雨的方法,对不同降雨强度与不同坡度下黄土坡面汇沙对细沟侵蚀的影响及贡献进行了研究,结果表明:细沟上方汇沙、细沟间汇沙、细沟径流剪切力对细沟侵蚀的影响,在不同降雨强度、不同坡度、不同降雨强度及坡度下皆可用三元对数方程描述;细沟上方汇沙、细沟间汇沙、细沟径流剪切力,以及细沟上方汇沙与细沟间汇沙及细沟径流剪切力三者的交互作用对细沟侵蚀的贡献率,在不同降雨强度下分别为13.18％、4.98％、61.2％及8.26％,在不同坡度下分别为4.73％、1.19％、73.65％及5.4％,在不同降雨强度及坡度下分别为10.84％、0.44％、65.22％及6.97％.     

典型黄土坡面土壤侵蚀特征及径流流速空间变化试验研究

为了明确土壤性质对坡面侵蚀方式作用机制的影响,本研究采用室内模拟降雨试验,选取黄土高原典型暴雨强度,在不同坡度条件下,对两种黄土的坡面侵蚀方式、形态特征、产流产沙过程及其相应径流流速的变化规律进行了研究。结果表明,绥德土径流量明显高于安塞土,10º、15º和20º时前者的平均径流量分别比后者高出51.1%、55.5%和63.0%,且前者更易形成细沟,使得其平均含沙量和平均产沙率分别是后者的1.14~3.59倍和2.50~8.48倍。在片蚀阶段,与绥德土相比,安塞土的含沙量较高,后者的平均含沙量是前者的1.24~1.73倍,但两种土壤的含沙量和产沙规律相同,均表现为先快速增加到最大值,然后逐渐降低到相对稳定状态,该现象证明片蚀的初期阶段主要受控于径流输沙能力,后期受径流的剥蚀能力控制。在细沟侵蚀阶段,绥德土细沟发育以沟头溯源侵蚀为主,崩塌作用频繁,该侵蚀形式不仅控制着细沟形态的总体特征,也导致含沙量和产沙率均急剧增加,该阶段平均含沙量是相应片蚀阶段的3.25~4.34倍。细沟沟口下方坡面存在明显的泥沙沉积带,表明细沟集中水流的搬运能力远高于坡面漫流,细沟侵蚀主要受径流输沙能力控制。两种土壤的径流流速均表现为坡面下部高于坡面上部,径流稳定后高于径流稳定前,总体来看,绥德土和安塞土上坡和径流稳定后的平均流速分别是下坡和径流稳定前的1.4倍、1.25倍和1.75倍、1.29倍,此外细沟侵蚀或侵蚀强度与微地貌形态之间的互馈作用对径流流速也有较大影响。     

不同坡面植被空间布局对坡沟系统产流产沙影响的实验

植被在有效控制水土流失、改善生态环境中具有重要作用。为探讨坡面不同植被覆盖度、不同植被空间布局对坡沟系统侵蚀产沙的影响,以4 m长坡面(坡度为20°)和3 m长沟坡(坡度为50°)组成的坡沟系统为研究对象,采用不同放水流量(3.2 L/min、5.2 L/min)的放水冲刷实验,研究了不同放水流量、不同植被覆盖度、不同植被布设部位对坡-沟系统及沟坡侵蚀产沙的影响。结果表明,在实验条件下,不同植被布设部位在相同放水流量、相同植被覆盖度条件下对坡沟系统侵蚀产沙有明显影响,而对产流量无明显影响;沟坡部分侵蚀产沙量不随坡面植被覆盖度的增大而减小,相反呈增大趋势。说明在实验条件下,对坡沟系统而言,仅在坡面部分布设植被,尽管能在一定程度上减少坡沟系统侵蚀产沙,但并不能有效减小沟坡部分的侵蚀产沙,甚至引起沟坡部分侵蚀产沙的增大。因此,水土流失治理过程中采取有效措施进行坡沟兼治将是减少水土流失的有效手段。     

陇中黄土高原丘陵沟壑区不同植被恢复模式下次降雨产流产沙特征

基于甘肃省清水县汤峪河径流小区2015—2017年的观测数据,研究不同植被恢复模式条件下坡面次降雨入渗、产流产沙特征。结果表明:不同植被恢复模式条件下的土壤入渗量与降雨强度呈二次函数关系,存在入渗量达到最大值的临界降雨强度。入渗速率与降雨历时可以用幂函数关系表达,符合考斯恰可夫入渗模型。不同植被恢复模式条件下的产流率在0.003 3～0.003 6 mm·min-1之间,相对裸地的减流率为54%～58%。产流率与降雨强度之间呈二次函数关系(R2>0.88),产流率的主要影响因素是降雨强度。径流含沙量平均值乔灌混合区(3.13 g·L-1)>灌木林(2.95 g·L-1)>乔木林(2.79 g·L-1)>草地(2.58 g·L-1),径流含沙量与降雨强度呈线性递增函数关系。裸地的产沙量显著高于各植被小区(P<0.05),是各植被小区的43～57倍,各植被小区的减沙率在93%～94%之间,减沙效益高于其减流效益。各植被坡面土壤流失量与降雨侵蚀力呈线性递增函数关系;产流率与侵蚀产沙率之间呈极显著正相关关系(P<0.01),二者间可采用二次函数关系表达。本研...     

坡长对坡耕地侵蚀产沙过程的影响

模拟降雨试验结果揭示出随着坡长增加,径流与侵蚀产沙量越大。当坡长小于１５ｍ时,累积侵蚀模数与降雨历时关系明显呈线性,其斜率随坡长增加而渐陡,当坡长大于１５ｍ时,累积侵蚀模数与降雨历时明显是非线性关系;坡长是导致细沟侵蚀的重要因素。细沟发育时,其侵蚀产沙量大约是坡面或细沟间的２－５倍;当细沟趋于稳定时,与无细沟发育的坡面水流含沙量值类似。在４０ｍ坡长小区,其单位时间侵蚀模数与２５ｍ坡长小区无明显差异,水流含沙量并无明显增加,显示出当坡长大于临界坡长时的变化过程规律。利用等高植物篱或等高地梗减少坡长有效值,可以大大降低单位面积上的土壤流失量。     

黄土丘陵沟壑区坡面径流侵蚀产沙过程的环境解释

应用数量分类(TWINSPAN)和排序(DCCA)方法对陕北吴起县典型坡面侵蚀产沙过程进行了环境解释。结果表明：环境因子对土样侵蚀产沙量的解释量达83%,其中DCCA排序轴前4轴的解释量占总排序轴解释量的69%,且分别与坡位、土壤质量、海拔、干根重显著相关。坡面径流侵蚀产沙量随冲刷时间呈波浪式变化,环境因子对侵蚀产沙过程影响甚微。坡面径流侵蚀产沙量按地形部位表现为梁峁顶<梁峁坡<沟坡<沟底,按地类则表现为灌木林<针阔混交林<针叶纯林<阔叶纯林。     

黄土坡面不同植被恢复阶段的减流减沙效益研究

在延安燕沟流域退耕黄土坡面,根据植被状况建立不同植被恢复阶段(耕地、草地、灌木地、林地)径流小区,分析在退耕还林(草)工程实施以后,不同植被恢复阶段的减流减沙效益。结果表明,与坡耕地相比,各小区的减流减沙效益为:林地>灌木地>草地,草地和灌木地的减沙效益大于减流效益。对比草地和灌木地刈割前后的产流产沙量,可以看出,草地和灌木的减流效益有80%以上是由于地表枯落物及根系拦蓄径流造成,刈割后产沙量有明显增加,表明处于植被演替初级阶段的近地表层生态功能仍然比较脆弱,仍需进行封育保护。     

基于SWAT模型的无资料流域产流产沙模拟

准确预报无资料地区的产流产沙,对土壤侵蚀治理具有重要的实践意义。为了研究南方红壤侵蚀区无观测资料流域的产流产沙情况,以福建省长汀县朱溪小流域为研究区,其次一级流域游屋圳子流域和高陂塅子流域分别为参证流域和无观测资料流域。采用相对误差(Re)、决定系数(R2)以及Nash-Sutcliffe效率系数(Ens)评价了SWAT模型在游屋圳子流域的产流产沙模拟的适用性,基于地形指数判定了两子流域的水文相似性。结果表明:SWAT模型适用于游屋圳子流域的产流产沙模拟;游屋圳子流域与高陂塅子流域具有水文相似性,说明两子流域间可以进行模型参数移植;经模型参数移植,模拟得2010年高陂塅子流域年径流量为1.32×107m3,年产沙量为2 200 t。模拟结果不仅为小流域的水土保持治理提供参考,也为其他无资料流域的产流产沙模拟提供方法借鉴。     

西宁盆地黄土区不同草本植物和坡形条件下坡面产流产沙特征

为进一步研究不同草本植物和边坡坡面形态对坡面产流产沙的影响,以西宁盆地毛鸡湾流域长岭绿化区作为试验区,设计了直形和阶梯形2种坡形,选取3种优势草本老芒麦(Elymus sibiricus Linn.)、垂穗披碱草(Elymus nutans Griseb.)和细茎冰草(Agropyron trachycaulum Linn.Gaertn.)作为试验供试种,通过人工模拟降雨试验,探讨了种植不同草本和坡形条件下,边坡坡面的产流、产沙和入渗特征。结果表明,在直形边坡中,裸坡坡面的产流时间小于种植草本植物坡面,且垂穗披碱草坡面和老芒麦坡面的形成产流时间相对较长,为4 min。与直形边坡相比,垂穗披碱草阶梯形坡面产流时间相对最长,为8 min;在直形边坡中,垂穗披碱草坡面和老芒麦坡面累积径流量、累积产沙量和径流系数相对最小,分别为51.42 L/min、160 g、14.98%,51.25 L/min、210 g、14.93%,细茎冰草坡面的累积径流量、累积产沙量和径流系数分别为96.97 L/min, 700 g, 28.25%;垂穗披碱草坡面和老芒麦坡面稳定入渗速率相对最大,其值为0.38～...     

黄土丘陵沟壑区极端降雨事件及其对径流泥沙的影响

半干旱黄土丘陵沟壑区是我国水土流失的重灾区。在全球气候变化的大背景下,极端降雨事件时有发生,加重了区域水土流失防治的难度。因此,科学界定极端降雨事件、进而探讨其发生规律及其对径流侵蚀的影响尤为重要。通过整理定西市安家沟流域(35°35′N,104°39′E)17年的降水和径流侵蚀数据进行统计分析。以降雨量和最大30min雨强为指标,采用世界气象组织的标准划分了极端降雨事件。结果发现:(1)研究区内极端次降雨事件的雨量和雨强的临界值分别为40.11mm和0.55mm/min,次降雨量的多年平均值为18.87mm。17年间共发生12次极端事件,5月、7月、8月份的发生概率分别为16.67%、50%和33.33%。因此最佳防治时间段为7、8月份。(2)聚类分析表明极端降雨事件可分为三类:降雨量和雨强都大于临界值,占25%;降雨量大于临界值,而雨强小于临界值,占41.67%;雨强大于临界值,降雨量大于多年平均值而小于临界值,占33.33%。(3)在极端降雨事件作用下,径流系数和侵蚀模数要比对应的多年平均值高。总体而言,降雨量和雨强都很高的极端事件的破坏性最强,但高历时低雨强的极端事件所产生的破坏也不容低估。(4)沙棘林在生长演替的过程中显著增强了抵御土壤侵蚀的能力,对极端降雨事件有很好的防治作用。抵御极端降雨最弱的是坡耕地,主要是由于受到坡度大、植被覆盖率低以及人为干扰等因素的影响。     

黄河中游流域环境要素对水沙变异的影响

目前 ,黄河中游地区流域的水沙变化主要以水文法和水保法研究为主。由于黄河中游具有明显的自然地带性分布特征 ,流域系统的水沙过程受到环境要素的综合影响。本文根据黄河中游河口镇至龙门区间已控一级支流的测站资料 ,采用地理环境要素法分析水沙变异及成因。研究表明 ,河龙区间流域径流量和输沙量与地理环境因子的影响密切相关。 2 0世纪 70年代以来 ,降雨减水减沙作用不断减小 ,随着水土保持措施的提高 ,人类活动减水减沙所占比重不断增大。 70年代与 80年代气候波动和人类活动影响的平均减水减沙作用分别为5 3 4 %、 2 8 6 %和 4 6 6 %、 71 4 %。     

黄河入海悬沙季节输送变化与输送机制的数值研究

Based on sediment and discharge flux data for the Yellow River, realistic forcing fields and bathymetry of the Bohai Sea, a suspended sediment transport module is driven by a wave-current coupled model to research seasonal variations and mechanisms of suspended load transport to the Bohai Sea. It could be concluded that surface sediment concentration indicates a distinct spatial distribution characteristic that varies seasonally in the Bohai Sea. Sediment concentration is rather high near the Yellow River estuary, seasonal variations of which are controlled by quantity of sediment from the Yellow River, suspended sediment concentration reaches its maximum during summer and fall. Furthermore, sediment concentration decreases rapidly in other seas far from the Yellow River estuary and maintains a very low level in the center of the Bohai Sea, and is dominated by seasonal variations of climatology wind field in the Bohai Sea. Only a small amount of sediments imported from the Yellow River are delivered northwestward to the southern coast of the Bohai Bay. Majority of sediments are transported southeastward to the Laizhou Bay, where sediments are continuously delivered into the center of the Bohai Sea in a northeastward direction, and part of them are transported eastward alongshore through the Bohai Strait. 69% of sediments from the Yellow River are deposited near the river delta, 31% conveyed seaward, within which, 4% exported to the northern Yellow Sea through the Bohai Strait. Wind wave is the most essential contributor to seasonal variations of sediment concentration in the Bohai Sea, and the contribution of tidal currents is also significant in shallow waters when wind speed is low.     

Numerical simulation on seasonal transport variations and mechanisms of suspended sediment discharged from the Yellow River to the Bohai Sea

Based on sediment and discharge flux data for the Yellow River, realistic forcing fields and bathymetry of the Bohai Sea, a suspended sediment transport module is driven by a wave-current coupled model to research seasonal variations and mechanisms of suspended load transport to the Bohai Sea. It could be concluded that surface sediment concentration indicates a distinct spatial distribution characteristic that varies seasonally in the Bohai Sea. Sediment concentration is rather high near the Yellow River estuary, seasonal variations of which are controlled by quantity of sediment from the Yellow River, suspended sediment concentration reaches its maximum during summer and fall. Furthermore, sediment concentration decreases rapidly in other seas far from the Yellow River estuary and maintains a very low level in the center of the Bohai Sea, and is dominated by seasonal variations of climatology wind field in the Bohai Sea. Only a small amount of sediments imported from the Yellow River are delivered northwestward to the southern coast of the Bohai Bay. Majority of sediments are transported southeastward to the Laizhou Bay, where sediments are continuously delivered into the center of the Bohai Sea in a northeastward direction, and part of them are transported eastward alongshore through the Bohai Strait. 69% of sediments from the Yellow River are deposited near the river delta, 31% conveyed seaward, within which, 4% exported to the northern Yellow Sea through the Bohai Strait. Wind wave is the most essential contributor to seasonal variations of sediment concentration in the Bohai Sea, and the contribution of tidal currents is also significant in shallow waters when wind speed is low.     

Axial and transverse deep-water sediment supply to syn-rift fault terraces: Insights from the West Xylokastro Fault Block,Gulf of Corinth,Greece

Deep-water syn-rift systems develop in partially- or transiently-linked depocentres to form complicated depositional architectures, which are characterised by short transport distances, coarse grain sizes and a wide range of sedimentary processes. Exhumed systems that can help to constrain the tectono-stratigraphic evolution of such systems are rare or complicated by inversion tectonics. Here, we document a mid-Pleistocene deep-water syn-rift system fed by Gilbert-type fan deltas in the hangingwall of a rift margin fault bounding the West Xylokastro Horst block, on the southern margin of the Gulf of Corinth, Greece. Structural and stratigraphic mapping combined with digital outcrop models permit observations along this syn-rift depositional system from hinterland source to deep-water sink. The West Xylokastro Fault hangingwall is filled by two distinct sediment systems; an axial system fed by coarse-grained sediment gravity flows derived from fault-tip Gilbert-type fan deltas and a lateral system dominated by mass transport deposits fed from an evolving fault-scarp apron. Abrupt changes in stratigraphic architecture across the axial system are interpreted to record changes in relative base level, sediment supply and tectonics. Locally, depositional topography and intra-basinal structures controlled sediment dispersal patterns, from bed-scale infilling of local rugose topography above mass transport complexes, to basin-scale confinement from the fault scarp apron. These acted to generate a temporally and spatially variable, heterogeneous stratigraphic architecture throughout the basin-fill. The transition of the locus of sedimentation from a rift margin to a fault terrace through the syn-sedimentary growth of a basinward fault produced regressive surfaces updip, which manifest themselves as channels in the deep-water realm and acted to prograde the system. We present a new conceptual model that recognises coeval axial and transverse systems based on the stratigraphic architecture around the West Xylokastro fault block that emphasizes the lateral and vertical heterogeneity of rift basin-fills with multiple entry points.