Impact of Land Use and Land Cover Changes on Surface Runoff and Sediment Yield in the Little Ruaha River Catchment

Little Ruaha River catchment (6370 Km2) in the Southern Agricultural Growth Corridor of Tanzania (SAGCOT), is one of the country’s most significant waterways due to its ecological composition and economic value. Regardless of its ecological and economical value, the regional hydrologic condition has been tremendously affected due to land uses alteration, influenced by different socio-economic factors. This study aimed to understand the associated impacts of the present Land Use Land Cover (LULC) change on the surface runoff and sediment yield in the Little Ruaha River Catchment. Hydrological modelling using Soil and Water Assessment Tool (SWAT Model) was done to quantify the impact of land use and land cover dynamics on catchment water balance and sediment loads. The calibration and validation of the SWAT model were performed using sequential uncertainty fitting (SUFI-2). The results showed that, for the given LULC change, the average annual surface runoff increased by 2.78 mm while average annual total sediment loading increased by 3.56 t/ha, the average annual base flow decreased by 2.68 mm, ground water shallow aquifer recharge decreased from 2.97 mm and a slight decrease in average annual ground water deep aquifer recharge by 0.14 mm. The model predicts that in the future, there will be a further increase in both surface runoff and sediment load. Such changes, increased runoff generation and sediment yield with decreased base flow have implications on the sustenance flow regimes particularly the observed reduced dry season river flow of the Little Ruaha River, which in turn cause adverse impacts to the biotic component of the ecosystem, reduced water storage and energy production at Mtera Hydroelectrical dam also increasing the chances of flooding at some times of the year. The study recommends land use planning at the village level, and conservation agricultural practices to ameliorate the current situation. Developing multidisciplinary approaches for integrated catchment management is the key to the sustainability of Little Ruaha River catchment.

Impacts of Land Cover Changes on Runoff and Sediment in the Cedar Creek Watershed,St.Joseph River,Indiana,United States

The relation between runoff and sediment and land cover is investigated in the Cedar Creek Watershed (CCW), located in Northeastern Indiana, United States. The major land cover types in this watershed are cultivated land, woodland and pasture /Conservation Reserve Program (CRP), which account for approximate 90 % of the total area in the region. Moreover, land use was changed tremendously from 2000 to 2004, even without regarding the effect of the crop rotation system (corn & soybean). At least 49 % of land cover types were changed into other types in this period. The land cover types, ranking by changing area from high to low series, are rye, soybean, corn, woodland and pasture/CRP. The CCW is divided into 21 sub- watersheds, and soil and water loss in each sub-watershed is computed by using Soil and Water Assessment Tool (SWAT). The results indicate that the variations in runoff and sediment have positive relation to the area of crops (especially corn and soybean); sediment is more sensitive to land cover changes than runoff; more heavy rainfall does not always mean more runoff because the combination of different land cover types always modify runoff coefficient; and rye, soybean and corn are the key land cover types, which affected the variation in runoff and sediment in the CCW.

Calculation method of composite foundation sedimentation of grouting pile with cover plate under embankment load

Grouting pile is a new soft soil foundation treatment method with characteristics such as no vibration, no noise, no soil compaction, light construction machines and quick construction velocity and so on. At present, study on reinforcement mechanism and design calculation method of composite foundation of grouting pile is initially started without design specifications, so it is usually required to draw on design specifications of stump pile when designing composite foundation of grouting pile while grouting pile has its characteristics and difference although reinforcement mechanisms and construction processes of two types of piles are similar. Sedimentation formula of composite foundation of grouting pile with cover plate is educed and a suitable deformation mode is proposed by aiming to deformation characteristics of composite foundation of grouting pile with cover plate under embankment load on basis of relevant sedimentation theories of composite foundation by combination of characteristics of composite foundation of grouting pile. The sedimentation calculation formula of grouting pile with cover plate under embankment load is educed according to balance relation of force and displacement coordination conditions by elastic theory and sedimentation calculation model established is validated by sedimentation monitoring documents of one expressway in China.

降雨和土地覆被变化对三川河流域水沙的影响分析

黄河流域气候变化和人类活动对流域水沙过程均产生了深刻的影响。该研究以晋西三川河流域为对象,基于1999-2019年实测水文数据和遥感影像,采用M-K法揭示降雨量、径流量与输沙量的变化特征,结合回归分析法阐明降雨和土地覆被变化对径流、输沙的影响。通过研究,可科学认识降雨和土地覆被变化对三川河流域水沙突变的影响,对黄河流域生态保护和高质量发展具有重要意义。

Effect of Different Remediators on the Control of Phosphorus Release from Landscape River Sediments

In this paper,different chemicals were added to sediments to control phosphorus release from river sediments by means of different dosing methods,thus reducing the concentration of organic pollutants in overlying water.Two remediators,aluminum sulfate and ferric chloride,were respectively added to six groups of experimental samples in three different covering methods,namely injection,mixing and tiling,and a control group was set up.The results showed that at the initially stationary phase of the experiment,the control effect of phosphorus release from sediments of mixing of aluminum sulfate was the most obvious,followed by tiling and injection into the mud;at the finally stationary phase of the experiment,the control effect of phosphorus release from sediments of injection of aluminum sulfate was the most obvious,followed by mixing and tiling.Under the same coverage,the inhibition effect of aluminum sulfate was more obvious than that of ferric chloride.This paper undertook research into the control effect of phosphorus release from sediments to provide a reference point for the control of water eutrophication in the days to come.

Organic carbon losses by eroded sediments from sloping vegetable fields in South China

Soil Organic Carbon(SOC) is the most important component of soil. Though small, it determines soil fertility and prevents soil losses. In this study, we examined relationships between the Particle–Size Distribution(PSD) of the eroded sediment and SOC loss, and evaluated the effects of plant coverage ratios(0%, 15%, 30%, 45%, 60% and 90%), slope lengths(2 m, 4 m), fertilizer treatments(unfertilized control(CK), compound N–P–K fertilizer(CF), and organic fertilizer(OF)) on SOC loss and the SOC enrichment ratio(ERSOC) in the eroded sediments. The experimental results showed that longer slope length and lower surface cover ratios produced larger surface runoff and the eroded sediments, resulting in larger SOC losses. The average SOC loss was greatest in the OF treatment and SOC loss was mainly associated with the eroded sediment. Surface runoff, which causes soil erosion, is a selective transportation process, hence there were more claysized particles(<2 μm) and silt-sized particles(2-50 μm) in the eroded sediments than in the original soils. SOC was enriched in the eroded sediments relative to in the original soil when ERSOC > 1. ERSOC was positively correlated with ER_(clay)(<2 μm)(R^2 = 0.68) and ERfine silt(2–20 μm)(R^2 = 0.63), and from all thesize particle categories of the original soil or the eroded sediments, more than 95% of SOC was concentrated in small-sized particles(<50 μm). The distribution of SOC in different-sized particles of the original soil and the eroded sediment is primarily associated with clay-sized particles and fine silt-sized particles, thus we conclude that as the eroded sediment particles became finer, more SOC was absorbed, resulting in more severe SOC loss.

Assessment of Land-Use and Land Cover Change Effect on Melka Wakena Hydropower Dam in Melka Wakena Catchment of Sub-Upper Wabe-Shebelle Watershed, South Eastern Ethiopia

Land degradation and sedimentation has been increasingly a crucial problem in upper Wabe-Shebele catchment, south eastern Ethiopia over the last two decades. Nevertheless, so far no detail research has been conducted to assess such problem. Therefore, the present study was conducted at Melka Wakena Catchment of Upper Wabe Shebelle Watershed to identify the trends of land use and land cover change and its effects on hydrology and land degradation. To achieve the objectives of the study different data sources such as satellite images, climate and rivers gage data;soil sample data were collected and analyzed using relevant corresponding up to dated software. Based on pre-defined criterion, available satellite images for the years 1986, 2011, and 2015 were analyzed using ERDAS, ENVI and ArcGIS softwares. The study catchment stream flow and soil erosion information were computed using SWAT model. MUSLE was employed to assess the amount of sediment yields and rate of soil loss existed in the study area. The study showed that significant land use and land cover changes were recorded during the past nearly three decades. This change has been directly affecting the hydrology and sedimentation of the catchment. The annual surface runoff varied between 45.65 mm and 332.29 mm. The amount of surface runoff was generally increased from 1990 to 2010, whereas decreased until 2013 before beginning the increasing trend. The result of the sediment yield analysis showed that there was a general increasing trend from 1992 to 2010 and then declined up to 2013 before it started the rising trend. From the simulated results, it was observed that the long-term mean soil loss was 20.22 t/ha. Sustainable integrated watershed management practices should be practically implemented throughout the landscape of the catchment from upper to down streams. Above all, dam buffer area needs to be demarcated and protected from the current settlement: cultivation and over grazing.

Sediment Yield Dynamics during the 1950s Multi-Year Droughts from Two Ungauged Basins in the Edwards Plateau, Texas

Sediment yield dynamics on the Edwards Plateau region of Texas was dramatically influenced by a multi-year drought that occurred there during the 1950s. To assess the effect of this drought on sediment yield, we used the Soil and Water Assessment Tool (SWAT) to identify the factors that contributed erosion and to propose potential mitigation measures in case of future drought recurrence. The basins of interest to this study were Brady Creek One (BC 1) and Deep Creek Three (DC 3), located in McCulloch County, Texas. Although the streams in these basins are not gauged, the land cover and reservoir sediment budgets have been assessed in a past study. Calibration of SWAT flow simulation was accomplished using parameter transfer from a gauging station located in San Saba River. The results showed that sediment yield from storms above 60 mm was five times more during and immediately after drought period than during continuous wet seasons. Approximately half of the total drought period sediment yield was from five major rainstorms. The multi-year drought coupled with historical high grazing intensity resulted in significant loss of plant cover, which was considered critical in determining erosion and sedimentation rates. To test this hypothesis, the model was run for the periods of high land cover (1990s) using the 1950s multi-year drought data which showed that sediment yield was 24% of that simulated for 1950s land cover. It was concluded that maintenance of surface cover could play a critical role associated with multi-year drought extreme events.

Estimation of Sediment Yield of Govindsagar Catchment, Lalitpur District, (U.P.), India, Using Remote Sensing and GIS Techniques

Soil erosion is a global phenomenon, which results in sedimentation and siltation of reservoirs of major rivers. Remote sensing data provide a synoptic view from which several surface parameters can be derived to assess the sedimentation yield in the reservoirs. Hence estimation of sediment yield has become one of the important tasks for planners, engineers and decision makers. The present study in Govindsagar catchment, Lalitpur District, Uttar Pradesh (India), has been carried out using IRS LISS III data to analyse land use/cover characteristics besides drainage basin characterstics. Subsequently, Sediment Yield Index (SYI) of Govindsagar catchment has been estimated using surface derivatives and morphometric parameters using empirical formulae. Integration of results obtained from satellite data and morphometric analysis suggests that the Govindsagar catchment has very low rate of sediment yield i.e. 0.07 ha·m/year indicating a gentle slope and sustainable land use practices in the catchment. Low sediment yield also suggests less erosion in the catchment areas and healthy land use/cover scenario.

多时间尺度小流域侵蚀产沙对土地利用/覆被格局的变化响应

为阐明多时间尺度小流域侵蚀产沙对土地利用/覆被格局的变化响应机制,该研究基于吕二沟流域1982—2020年逐日降雨、水沙实测资料和土地利用/覆被数据,综合运用K-均值聚类法、多元回归分析等方法,从年际和年内月际2个时间尺度对比分析了不同土地利用/覆被格局下的流域侵蚀产沙变化及其与泥沙连通性指数的关系。结果表明:(1)1982—2020年间,吕二沟流域由耕地为主体向农林草复合结构转变、泥沙连通性指数显著下降,可将整个研究期划分为1982—1985年、1986—1990年、1991—2000年和2001—2020年共4个阶段,分别对应土地利用/覆被格局Ⅰ、Ⅱ、Ⅲ和Ⅳ。(2)随着以林草地增加为主的土地利用/覆被变化,流域产流、产沙能力减弱。相较土地利用/覆被格局Ⅰ,土地利用/覆被格局Ⅳ的年均径流深显著降低;后期土地利用/覆被格局(Ⅲ和Ⅳ)下的汛期月产流产沙能力显著小于前期(土地利用/覆被格局Ⅰ)。(3)基于月降雨量、月最大日降雨量和月侵蚀性降雨日数3个降雨指标,可将研究期内的汛期月降雨划分为4种类型:小雨量、弱侵蚀性的A型,中雨量、弱侵蚀性的B型,大雨量、中侵蚀性的C型,大雨量、强侵蚀性的D型;在大雨量中侵蚀性的C型降雨下,不同土地利用/覆被格局间的月际径流深和产沙模数均不存在显著差异(P>0.05)。年际和月际尺度下,小流域产沙模数均与泥沙连通性指数呈指数递增关系,但C雨型下的关系减弱。研究为干旱半干旱区流域土地利用/覆被格局优化配置和功能提升提供科学依据。

适用于明渠流及冰盖流的统一泥沙起动流速计算方法初探

冰盖是北方高寒地区河流冬季常见的一种自然现象。冰盖的出现改变了河流的运动状态,由原来的明渠流变为覆盖流。受冰盖糙率影响,垂线流速分布相应变化,进而影响河床泥沙输移。为进一步探讨冰期河床泥沙输移演变规律,基于Einstein假定,采用滚动起动模型,考虑冰盖下糙率变化、黏性淤积物干重度、相对暴露度对泥沙起动的影响,从理论上推导出了适用于冰盖流的泥沙起动流速公式,并与已有试验数据对比,相对误差集中在1%~10%之间;同时,探讨了本文公式对于明渠泥沙起动的适用性,即当冰盖糙率为0时,可视为明渠流泥沙起动流速计算公式,与实验数据对比,相对误差范围为0%~0.86%,亦可满足计算精度要求。

模拟降雨条件下不同草本植被对产流产沙的影响

为了探讨不同草本植被对坡面产流产沙的影响,在人工模拟降雨条件下,选择福禄考、佛甲草、蓝羊茅,设计坡度为10°;早熟禾、黑麦草、高羊茅,设计坡度分别为5°、10°、15°,进行试验研究。研究结果表明:不同草本植物均能有效降低土壤的产沙量与产流量,起到保持水土、修复生态的作用。相同草本,不同坡度下,坡度越大,产流、产沙、土壤侵蚀量越大,作用系数也越大。

拉萨河流域水沙过程模拟及对植被覆盖和气候变化的响应

针对青藏高原日趋严重的水土流失现象,以位于青藏高原中南部的拉萨河流域为研究区域,通过搭建流域月尺度SWAT模型,探究植被覆盖和气候变化对流域水沙演变的影响。主要结论如下:(1)SWAT模型适用于拉萨河流域水沙模拟。(2)1991-2010年植被覆盖整体上呈退化趋势,植被覆盖变化对年径流变化的影响较弱,而流域输沙量对植被覆盖变化的敏感程度较显著,尤其在极端恶劣植被覆盖情景下,流域年均输沙量增加约70.15%。(3)气温升高2℃时,降水变化率每增加10%,年径流和年输沙量变化率则分别增加16.01%和28.70%。不同气候变化情景下,输沙量和径流的变化趋势并非总是完全一致。

基于土壤颗分粒径的泥沙来源量化研究

[目的]揭示黄土高原风水复合侵蚀区风力作用对水蚀的影响,为具有不同泥沙粒径侵蚀物质来源识别提供一种有效的方法支撑,也为风水复合侵蚀区侵蚀泥沙来源辨识提供理论参考。[方法]以覆沙模拟风蚀产物,基于室内模拟试验,研究覆沙之后坡面侵蚀发育特征,同时为了有效区分不同时刻侵蚀物质的来源,尝试采用泥沙粒径作为指纹因子进行侵蚀泥沙来源贡献的辨识。[结果]不同泥沙粒径组的3个指纹因子(粒径范围分别为:26.303~34.674,104.713~138.038,138.038~181.970μm)通过检验被确定为最佳指纹因子。基于最佳指纹因子,通过多元混合模型计算得出,在对同一土槽进行的3个阶段模拟降雨试验中覆沙层和黄土层的平均泥沙贡献率分别为48.2%和51.8%,24.8%和75.2%,6.8%和93.2%,且MAF>0.8。覆沙层的泥沙贡献率为第一阶段试验>第二阶段试验>第三阶段试验,计算结果与DEM相吻合。[结论]泥沙源地和侵蚀泥沙中的不同泥沙粒径组可作为指纹因子进行泥沙来源辨别,复合指纹法具有较好的适用性。

查干湖沉积物水界面钨的空间分布及污染特征

选取松嫩平原第四纪冰川堆积区内查干湖为研究对象,利用薄膜扩散梯度技术获取不同点位沉积物-水界面钨的原位高分辨信息,探讨了钨的空间分布及污染特征。结果表明:查干湖各点位钨在上覆水的含量大于在沉积物中含量;采用地累积指数评价法对查干湖各点位钨的污染程度进行分析,发现查干湖沉积物各点位目前未受到钨污染。

DEM和土地利用分辨率对SWAT水沙模拟效果的影响——以泾河流域为例

DEM和土地利用的数据精度影响水文模型的模拟效果。以泾河流域为对象,选取毛家河、杨家坪和张家山3个水文站作为控制站,分别利用9组不同分辨率的DEM和土地利用数据(分辨率范围均为30~3000 m)构建了100个SWAT模型,探究输入数据精度对水沙模拟效果的影响,并采用TOPSIS理论方法对模型进行综合评价。研究表明:DEM分辨率会影响流域的边界和河网提取,且流域特征信息会随分辨率的降低而发生丢失;当DEM分辨率低于1000 m时,需使用SWAT中的Burn in工具,才能完成流域边界与河网的准确提取;HRU的数量随DEM分辨率的下降而减少,而土地利用分辨率对HRU数量的影响不显著;当分辨率变化较大时,DEM对参数敏感性造成的影响要大于土地利用;在构建的毛家河、杨家坪和张家山3个站点的模型中,DEM和土地利用分辨率的最优组合分别为750和300 m、30和90 m以及150和3000 m。该研究可为流域水沙模型构建与模拟精度提升提供方法与技术参考。

蔗区小流域泥沙有机碳入河负荷的时空变化特征及其影响因素

[目的]针对广西红壤区典型小流域坡耕地甘蔗土壤有机碳流失问题,探究其流失时空特征和影响因素,解析流域泥沙有机碳在甘蔗不同生长时期入河负荷时空变化,为揭示自然降雨侵蚀下土壤有机碳流失的影响机制提供科学依据。[方法]试验区位于广西壮族自治区崇左市扶绥县客兰水库水源区那辣小流域,流域分为下游子流域(S 1)和上游子流域(S_(2),S_(3))。利用无人机技术和径流泥沙自动监测—采样系统对甘蔗4个生长时期(苗期、分蘖期、伸长期和成熟期)入河泥沙有机碳及植被覆盖度等进行监测,并利用皮尔逊相关分析,确定入河泥沙有机碳与降雨径流、植被覆盖度和施肥等影响因素的关系。[结果]①甘蔗苗期的流域泥沙有机碳入河负荷占整个生长期总流失量的61.1%,显著高于其他生长期,其特征为苗期(5.1 kg/hm^(2))>成熟期(1.6 kg/hm^(2))>伸长期(1.4 kg/hm^(2))>分蘖期(0.3 kg/hm^(2))。②流域降雨径流和植被覆盖度与泥沙有机碳入河负荷呈极显著相关,分别解释了泥沙有机碳入河负荷生长期变化的45%和54%;而流域施肥和土壤容重与泥沙有机碳入河负荷呈显著相关,分别解释了泥沙有机碳入河负荷生长期变化的79%和36%。[结论]流域入河泥沙有机碳流失变化主要是由降雨径流、植被覆盖度、施肥和土壤容重所引起。在蔗区小流域,通过增加植被覆盖以减少地表径流的冲刷及调控施肥时间,对降低土壤有机碳流失具有重要作用。

污染底泥修复治理技术研究进展

综述了疏浚、覆盖、化学处理和生物处理等底泥修复治理技术的研究进展,并指出该研究领域尚需解决的技术难题。

玄武湖底泥营养物释放的模拟试验研究

对南京市玄武湖底泥的营养状况进行分析 ,并模拟复水试验 ,研究其水质情况及其富营养化程度 。