The impact of environmental changes on the sediment loads of Norwegian rivers

The impact of unusual events on the sediment dynamics in rivers is discussed in this paper. The increase in the number of extreme precipitation events and other unusual weather events in Norway strongly suggests that weather conditions are changing. It is difficult to monitor sediment transport during large magnitude floods. It is however well known that they may deliver substantial amounts of sediment. The suspended sediment load in the upper Atna river during the springflood in 1995 was 44 times the mean load measured during the preceding years. The recurrence interval of this flood was estimated to be 100–200 years. The conditions during the occurrence of a particular flood event may also be of considerable importance and measurements during rainfall on frozen ground have indicated unusually high runoff and erosion rates.The seasonal distribution of runoff in several parts of Norway has changed in recent years and higher winter temperatures have produced an increase in the frequency of flood events. A very long lasting flood caused by a prolonged period of rain occurred in the Vikka stream during September to December 2000. The availability of sediment increased with the increasing soil moisture content in the area. As the ground became saturated, more active slope processes caused erosion rates to increase markedly. The combined effects of climate change and human impact on sediment transport in rivers appear to enhance downstream sediment delivery. Flood protection works along river channels prevent sediment from being deposited on the floodplain. River channels that have been lowered in order to reduce groundwater levels in agricultural floodplain areas will experience the same effect. During the last decade extensive ecological changes have taken place in the coastal areas of southern Norway as 90% of the sugar kelp forest has been lost. This change has been attributed to an apparent increase in sediment delivery to the sea along with a rise in sea temperatures.     

1960-2010年延河水沙特征及其对退耕工程的潜在响应

河流水沙特征与流域降水量和下垫面变化密切相关.为揭示流域降雨以及退耕还林对延河流域水沙特征的影响,本文以延河甘谷驿站控制区1960-2010年流域降水量、河流径流量和输沙量实测数据为基础,统计分析了延河水沙变化特征及其对流域降水量的响应,并对比分析了退耕前、后(以2002年为界)延河水沙变化.结果表明:在1960-2010年间,延河甘谷驿站控制区年及汛期(6-9月)降水量、径流量和输沙量呈波动递减趋势,汛期降水量、径流量和输沙量值约占年值的64.8％、71.7％和98.1％;年及汛期输沙量与径流量呈极显著正相关关系,径流量变化可分别解释年及汛期87.6％和92.2％的输沙量变化,降水量变化可分别解释年及汛期22.7％和23.6％的输沙量变化;退耕后流域年及汛期平均输沙量、径流量和径流系数显著低于退耕前,剔除退耕前后降水量差异影响,退耕工程对年及汛期累计输沙量变化分别贡献87.5％和86.9％,对年及汛期累计径流量变化分别贡献77.4％和75.4％.研究阐明退耕可显著降低年及汛期平均径流量、径流系数和输沙量.     

西安市东郊渭河河漫滩沉积与洪水变化

[目的]通过揭示历史时期洪水的演变,科学地预测洪水的发生,以求减少洪水灾害造成的损失。[方法]通过分析西安市东郊水流村剖面106个样品的粒度组成,研究了西安市渭河近230a来的洪水事件。[结果]剖面厚度约5m,沉积物主要由粗粉砂、极细砂、中砂和粗砂组成,在各层中变化明显,能够指示古洪水的变化。粒度成分和粒度参数指示,研究剖面中的洪水沉积可分为21层,表明西安市渭河近230a来至少发生了21次洪水事件,各阶段的洪水动力大小为:第18阶段17阶段15阶段16,19阶段21阶段4,5阶段3阶段1,2阶段6,7阶段10阶段11阶段8,9阶段13,14阶段12阶段20阶段。在研究剖面发生的21次洪水事件中,除第20次洪水外,其余洪水发生时河漫滩上的洪水深度均大于2m,均为大洪水事件。[结论]洪水沉积层的分布和粒度成分指示,第3,5,7,8次大洪水的发生是由于当年降水量的显著增加造成的,其余次洪水的发生可能是当年降水量增加造成的,也可能是当年降水量没有增加而是由于当年降水量集中造成的。     

水土保持是江河治理的根本——关于'98长江洪水灾害的思考

由于长江中上游植被减少,土层减薄,水源涵养能力下降,造成暴雨径流加速汇集,加之大量泥沙下泄,淤积江河湖库,降低了调蓄和宣泄洪水能力。因此,水土流失是加剧’９８长江洪水灾害的重要原因。森林具有涵养水源、固土防蚀的功能,恢复植被是水土保持的措施之一,但其保持水土的作用有限。据观测,就一次降雨而言,森林最大截蓄雨量不超过３０ｍｍ,随着降雨过程的延续,森林拦蓄降雨的作用基本消失。大江大河的防洪减灾,除搞好干流水库、平原蓄洪区的建设,堤防和河道的整治外,尤其要搞好面上的水土流失治理。     

小型河流泛滥平原生态蓄洪措施设计

[目的]在保证防洪和尽量不影响现有土地利用和水工设施的前提下,设计一系列措施将洪水重新引入泛滥平原,促进泛滥平原蓄集洪水,使得水资源配置更加合理。[方法]结合当前的河流整治工作,通过影像分析、实地调查等方法,依据生态学的理论进行生态蓄洪设计研究。[结果]以山西省宁武县恢河的一个泛滥平原为例,提出泛滥平原分洪网的生态蓄洪设计,具体包括浅滩深潭序列渠、池塘链分洪渠、分洪出入口等措施,将河道中的洪水引入泛滥平原并蓄集下来,尽可能地恢复泛滥平原的蓄水功能,调节河流流量、消洪减灾。[结论]泛滥平原分洪网设计符合河流生态系统自然规律,在保证经济、社会发展的前提下,最大程度地发挥小型河流泛滥平原的生态效益,重视发挥小型河流的生态蓄水功能,恢复健康的河流和流域。     

大理河流域不同时间尺度水沙变化影响因素及趋势研究

近几十年来黄河中游水沙特征有所改变,以黄河中游典型流域大理河为例,通过分析流域气候及下垫面变化.探求流域产流、产沙量变化的原因及趋势.结果表明:流域水土保持措施的减水、减沙效益从1972年后开始显现,1960年代至1990年代,大理河流域产流、产沙量出现了一个先减少再增大的过程.以1960年代为基准,1970年代降雨与下垫面产流能力对流域产流量减少的影响比较接近(51.7%.42.2%),而在1980,1990年代降雨的影响要小于下垫面产流能力的影响(1980年代为27.0%,64.1%;1990年代为38.4%,54.9%);但在汛期尺度上,降雨、下垫面产流能力对流域产流量的影响此消彼长,随时间变化看不出什么规律.受气候以及水土保持措施等的影响,未来大理河流域多年平均尺度下流域产流量、产沙量将会减少,但在某些小的时间尺度(次暴雨)内的产流量、产沙量将有增大的可能;水力侵蚀将会减少,但风力侵蚀却有加强的趋势.     

Spatial Variability of the Particle Size Composition of Overbank Floodplain Deposits

An important feature of overbank floodplain deposits is the spatial variability of their particle size composition. Analysis of such spatial variability can assist in developing an improved understanding of the transport and deposition of suspended sediment on river floodplains during overbank flood events, in investigating the fate of sediment-associated contaminants and in calibrating existing floodplain sediment deposition models. The study reported in this paper investigates the spatial variability of the grain size composition of overbank floodplain deposits at different spatial scales, through analysis of surface sediment samples collected from frequently inundated floodplain sites on the Rivers Cuhn, Stour and Severn in the UK. Significant lateral and downstream variations in the grain size composition of the sediment deposits have been documented at the study sites, and the results obtained have been interpreted in terms of the processes governing overbank floodplain flow and sediment transport and deposition, which are influenced by a number of factors including floodplain geometry and topography.     

Fluvial development and the sediment regime of the lower Calder,Ribble catchment,northwest England

In the lower reaches of the Calder (Lancashire) tributary of the Ribble catchment (northwest England), five river terraces set into the surrounding glacial terrain have been mapped and their underlying sediments radiocarbon dated. The earliest terrace (T1) reflects sandur-style deposition during deglaciation and it aggraded in a reach cut into glacial diamict and glaciolacustrine muds. Incision below T1 spanned the start of the Holocene, driven by a combination of reduced sediment supply under a stabilising landscape and lower base-levels. T2 had aggraded and was being abandoned by 4000 BC; its formation latterly involving a period of comparative stability in terms of channel migration, perhaps a function of extensive forest cover and sea levels reaching above present day levels. The last 3000 years were marked by substantial changes in the sedimentary regime, with increased and varying sediment supply driving cycles of cut-and-fill and greater lateral channel migration. These changes coincided with the first widespread and substantial reductions in forest cover and a progression towards an agricultural landscape. Between the aggradation of terraces T3 and T4 there was a substantial increase in sediment supply, which is broadly in keeping with the erosion history in the surrounding uplands. This sediment slug appears to have induced a switch from highly sinuous meandering to lower sinuosity channels characterised by lateral scroll-style migration. Late Holocene vegetation changes, particularly woodland removal, driven by anthropogenic land-pressure appear to have rendered the floodplain prone to channel migration and the landscape more susceptible to erosion.     

基于双土槽试验研究的黄土坡面侵蚀产沙过程

 定量分析梁峁坡面各侵蚀带之间侵蚀过程中的相互作用及其影响机理,将为坡面侵蚀预报模型的建立提供重要的理论基础。利用供沙土槽和试验土槽双土槽径流小区,研究不同上方汇流含沙量、不同降雨强度和不同地表面条件下的黏黄土陡坡面(15°)上方汇流汇沙,对坡下方侵蚀产沙过程的影响。研究结果表明:上方汇流汇沙对坡面侵蚀产沙过程有重要影响,上方来沙不但被径流全部搬运,而且上方来水在试验土槽引起了净侵蚀产沙量,坡面侵蚀现象为侵蚀-搬运过程占主导地位。对于疏松土和紧实土处理,上方汇流引起坡下方的净侵蚀产沙量,分别占试验土槽全部产沙量的31.1％-97.3％和45.1％-89.7％。上方汇流引起坡下方净侵蚀产沙量随降雨强度的增加而增加,同时受土壤容重和下垫面细沟侵蚀发展过程的综合影响。土壤容重影响坡面侵蚀的发生和发展,而坡面侵蚀产沙过程与细沟发育过程相对应。     

南方红壤区典型水土流失治理小流域的洪水径流泥沙特征

为探究南方红壤区经长期水土流失治理小流域的水沙特征,该研究收集长汀县朱溪河小流域2017—2020年降雨及洪水水沙数据,通过冗余分析、多元逐步回归方程、含沙量-流量滞回曲线等方法进行分析。结果显示：（1）流域年洪水径流深和泥沙量分别为282.30～892.50 mm和35.80～179.50 t/km²,洪水事件的产沙模数集中在0～20.0 t/km²,但总泥沙量由大于5.0 t/km²的少数事件决定;（2）降雨量、30 mim的最大雨强和降雨侵蚀力是影响洪水径流泥沙的主要降雨特征,对径流、泥沙变化的解释度分别为68.99%和49.28%,通过主要径流特征估算泥沙量、平均含沙量和最大含沙量,拟合优度达0.624～0.870;（3）洪水事件共出现6种含沙量-流量滞回关系,其中线型出现频率（55%）最高,该类事件中含沙量随流量的变化具有分阶段特征,临界含沙量约为0.1 g/L。经过长期的水土流失治理,红壤区小流域的洪水泥沙量普遍较低,且主要受径流量影响,洪水事件的滞回关系表明流域的泥沙供应通常处于持续少量的状态,研究结果有助于揭示红壤区土壤侵蚀的发展趋势。     

2007-2017年府谷-龙门段河道冲淤特征及其动力机制

[目的]河道演变是水流、泥沙与河床边界相互作用的结果,对水利工程的安全、洪涝灾害的防控有显著的影响。黄河中游府谷—龙门段位于晋陕峡谷地带,以黄土高原沟壑侵蚀地貌为主,流经的黄土高原地区是黄河泥沙的主要来源,因此研究该河段的河道冲淤特征及影响因素对控制黄河中游水土流失有重要意义。[方法]基于府谷、吴堡、龙门3个典型水文站径流泥沙及河道断面数据,分析了2007—2017年府谷—龙门段河道冲淤特征及相关影响因素。[结果](1)近11年来府谷—龙门段河道整体表现为冲刷,其中府谷—吴堡段表现为河道冲刷量逐渐减小,吴堡—龙门段表现为河道冲刷逐年加剧。(2)府谷—吴堡段呈水减沙增的趋势,吴堡—龙门段整体表现为水多沙少,两河段河道冲淤量与水流含沙量变化同步。(3)府谷—吴堡段悬移质泥沙中值粒径呈增加趋势,河道冲刷变缓;吴堡—龙门段悬移质泥沙中值粒径呈减小趋势,加剧河道侵蚀。(4)府谷站入黄泥沙量增加,河道侵蚀力降低,河道冲刷变缓;吴堡站入黄泥沙量减少,河道侵蚀力增强,河道处于冲刷的状态。[结论]径流泥沙的变化在很大程度上影响了府谷—龙门段河道冲淤。在生态环境有所改善的背景下,研究该河段河道冲淤特征及动...     

降水和土地利用变化对罗玉沟流域水沙关系的影响

为探讨降水和土地利用变化对流域水沙关系的影响,以黄土高原丘陵沟壑区罗玉沟流域为研究区域,利用流域25年(1986—2010年)的年降水量、年径流量和年输沙量以及土地利用变化资料,分析罗玉沟流域水沙演变规律和水沙关系变化。结果表明:在1986—2010年罗玉沟流域年降水量和汛期降水量基本保持平稳,无明显的增减趋势,而流域年径流量和年输沙量整体呈波动递减的变化趋势,降水与径流相关分析得出,汛期产流产沙对流域年径流量和年输沙量影响最显著。对不同时期流域水沙变化分析,土地利用方式改变,主要是梯田、林草等水土保持措施,对于流域减水减沙作用有限,梯田和林草面积的增加并未明显改变流域水沙关系,淤地坝等工程措施对黄土高原丘陵沟壑区流域减水减沙具有重要作用。研究结果可为黄土丘陵沟壑区水土流失治理及水土保持措施布设提供理论依据。     

近120年来高陵渭河河漫滩沉积物磁化率指示的气候变化

根据史料记载以及高陵渭河河漫滩沉积物共110个样品磁化率、粒度成分的测定分析,研究了近120年来,该地区沉积物在0～4.0 m深度上磁化率变化特征。结果显示,高陵渭河河漫滩磁化率随深度具有高低变化节律,整个剖面分6个阶段,第1,3,5阶段频率磁化率值高,第2,4,6阶段频率磁化率值低;沉积物磁化率与粒度成分有较好的相关性,表现为频率磁化率值低,沉积物粒度成分细,反之则反。磁化率反映了沉积时期水动力强弱变化,第1,3,5阶段对应洪水规模大的时期,指示沉积时水位高,水量大;第2,4,6阶段对应洪水规模小的时期,指示沉积时水位低,水量小。洪水规模的变化间接反映了该地区近120年来气候的波动变化特征。     

砒砂岩区沙棘林生态工程减洪减沙作用分析

 通过"水保法"计算沙棘林在砒砂岩区的减洪减沙效益,分析晋陕蒙砒砂岩区沙棘林生态工程的减洪减沙量,以及对研究区直接入黄支流的减洪减沙作用。结果显示:研究区流域内沙棘林占流域内总林地面积的比例逐年增大,沙棘林的减洪减沙量也逐年增大,从2002年到2008年,皇甫川、孤山川、窟野河等三支流沙棘林平均每年总减洪量480.84万m3,总减沙量302.65万t。研究结果对砒砂岩区配置水土保持措施有重要的参考价值。     

基于混合产流模式的黄土高原流域水沙过程耦合模拟

为深入理解黄土高原干旱半干旱地区复杂地貌条件下流域水沙运移规律。基于垂向混合产流机理和运动波方程，构建分布式流域水文模型，耦合流域土壤侵蚀和泥沙输移过程模拟模块，并考虑梯田对水沙过程的影响，建立适用于黄土高原的分布式流域水沙过程模型。选取黄土高原延河支流西川河流域多年实测场次洪水过程的径流泥沙资料，对模型进行率定和验证。径流模拟的纳什效率系数在0.56以上，平均值超过0.70,模拟次洪过程的峰形、峰值、峰现时间与实测过程具有较好的一致性；侵蚀产输沙模拟精度较低，其纳什效率系数均值率定期为0.79,但验证期仅为0.45,模拟结果整体趋势与实测值较一致，但输沙量模拟峰值比实测值偏低。模型可以较精确地模拟黄土高原流域洪水产汇流过程，但输沙量模拟值偏低，一方面由于产汇流模块的误差传递；另一方面，对重力侵蚀考虑不足。因此，未来模型将考虑滑坡、崩塌等重力侵蚀过程，提升模拟精度和效率，为流域水沙过程模拟与流域综合治理提供有效工具。     

Hyporheic flow as a potential geomorphic agent in the evolution of channel morphology in a gravel-bed river

Morphologic and hydrologic properties of head-cut gullies formed in meandering bends of a gravel-bed river in northern Japan were examined to investigate their topographic development. head-cut gullies had incised to 2 m below the floodplain surface and had perennial seepage outflows. Because no surface runoff was observed across the meandering necks, we hypothesized that hyporheic flow erosion cutting into the down-river edge of the meandering necks is one factor for the development of head-cut gullies. Several topographic features caused by sapping and piping erosion were observed within the head-cut gullies. A tracer experiment and examination of the water table, water chemistry, and water table responses in wells on the floodplain and within the head-cut gully revealed that significant preferential hyporheic flow occurred between coarse cobble and fine sediment layers of the floodplain materials. During a storm event, water tables around the head-cut gully quickly responded to changes in the water table of the stream channel; this result also suggests that hyporheic flow occurred across the meandering bends. Hyporheic flow around the head-cut gullies had higher hydraulic conductivities and preferential flow paths that may relate to buried beds of paleochannels. An erosion model suggests that it is unlikely that hyporheic flow alone had enough energy to account for all the soil erosion. Thus, a combination of hyporheic flow (sapping erosion) and channel erosion (bank erosion) appeared to contribute to the formation of the head-cut gullies. Hyporheic flow is an important component in the geomorphic evolution of channels and the floodplain in a gravel-bed river.     

Application of catchment scale sediment delivery model INCA-Sed to four small study catchments in Finland

The novel catchment scale erosion and sediment delivery model INCA-Sed was applied to four small study catchments in Finland. Three of these, the Mustajoki, Haarajoki and Luhdanjoki, are headwater catchments located in central Finland. The associated rivers have differing morphological characteristics varying from a ditch to a small river. Soil textures in the area are derived from moraine deposits and are largely sand and gravel. The Mustajoki and Haarajoki catchments are forested and only 10% of the area is under cultivation. In the Luhdanjoki catchment agricultural fields cover 40% of the area. The fourth study site, the Savijoki catchment, represents an intensively cultivated area in south-western Finland. Cultivated fields cover 40% of the catchment area, and they are located on clay soils along the river. The INCA-Sed model was able to capture both the correct magnitude and seasonal behaviour of suspended sediment concentrations in the rivers, as well as the correct magnitude of the sediment load derived from different land use classes. Small differences in river morphology and soil textures between the catchments have a significant influence on suspended sediment concentration in the rivers. Correct timing of suspended sediment concentration peaks is not, however, captured by the INCA-Sed model, which may be due to the stochastic nature of erosion and delivery processes at the catchment scale which are not taken into account in the parameter values used in the modelling. Parameter values were estimated from previous researches based on average process loads. The INCA-Sed model was, however, generally found to be a suitable tool for evaluating effects of land use change on erosion and sediment delivery in Finland as it correctly reproduces spatial and seasonal variations in sediment delivery, in addition to annual averages with spatial and temporal variations.     

金沙江流域水沙变化及其驱动机制

为了探究金沙江流域控制水文站屏山站水沙序列的趋势及突变特性,量化不同驱动因素对水沙变化的贡献。基于金沙江流域1954—2016年径流和输沙数据,从长时期及场次事件两个角度揭示了水沙关系的动态变化特征。结果表明：(1) 63年间,径流量年均变化速率为-1.16×10⁸m³/a;输沙量年均变化速率为-2.0×10⁶t/a; 1998年长江流域发生特大洪水,水沙序列在该年发生突变;(2)水沙关系的特征参数a值在1998年前后由上升改为下降趋势,退耕等坡面水保措施在1998年后发挥了重要作用;b值始终下降,河道影响因素始终发挥减沙作用;在场次降雨尺度上,流域径流-悬移质泥沙环路(C-Q环路)以顺时针形环路为主,表明坡面泥沙物源充足,是影响流域产沙的重要因素;(3)流域内降水、温度及NDVI与径流和输沙之间有明显的相关性,人类活动与降水因素对径流量的贡献比为-1∶2,而输沙量主要受人类活动影响,对应的贡献比为-6∶1。综上,金沙江流域63年间的径流输沙受多种因素综合影响,径流量的变化主要由于降水的变化,输沙量受人类活动影响更大。     

窟野河水沙变化发展趋势预测

窟野河是黄河河龙区间水土流失严重的一条多沙粗沙支流,流域内人类活动频繁,神府东胜煤田正在开发,其水沙变化发展趋势令人关注。经分析预测,神府东胜矿区一、二期工程排弃的土石数量为6.3亿t,1987～2000年平均每年增沙1130～1350万t;2000年前规划治理减沙效益为37.1％,减水效益为37.8％;一次洪水垮坝冲失的泥沙,将增加该次洪水泥沙量的13.3％～36.5％;河道淤积会加重防洪困难,其泥沙还可能集中排入黄河;丰水年份洪水泥沙有可能剧增,枯水年份水量进一步减少,甚至会出现水资源危机。     

Phosphorus and Suspended Sediment Loads in Base-Flow and Runoff Events: A Case Study of a Small Stream in NW Spain

This study focuses on the role of runoff events in influencing concentrations and export of suspended sediments and phosphorus in a headwater stream draining an agroforestry catchment in northwestern Spain. Large differences exist between suspended sediment and phosphorus (P) concentrations measured during base-flow conditions and runoff events, with a higher delivery during runoff events. Suspended sediment and phosphorus exports were 29.44 and 0.08 kg ha^?1 y^?1 respectively, with more than 50% delivered during runoff events (12% of the year). The relative contributions of phosphorus forms to the total annual export were 75% and 25% as particulate and dissolved phosphorus, respectively. Soil erosion is the main source of suspended sediment and phosphorus in the stream.