The water balance of Lake Kyoga,Uganda

Abstract

The annual water balance of Lake Kyoga is estimated by a comparison of upstream and downstream flows in the Nile channel during a period of reliable measurements (1940–1977), supported by rainfall records over the basin. The relative contributions of net lake rainfall and tributary inflows are estimated. Changes in annual rainfall and seasonal distribution are examined.

Editor Z.W. Kundzewicz

Citation Brown, E. and Sutcliffe, J.V., 2013. The water balance of Lake Kyoga, Uganda. Hydrological Sciences Journal, 58 (2), 342–353.     

大青山河谷地貌特征及新构造意义

论述了大青山河谷地貌的基本特征,河谷地貌的形成和演化明显地受大青山山前断裂带的控制。在山前断裂强烈活动的地段,河流深发呈峡谷,发育多级河流阶地,河谷纵剖面为上凸形,谷底宽度与谷肩山高度之比Ｖｆ值较小;在山前断裂活动较弱的地段,河流侧蚀呈宽谷,河流阶地级数较少,河谷纵剖面为下凹形,Ｖｆ值较大。河谷纵剖面凹度与大青山抬升幅度线性负相关。     

River system discontinuities due to lateral inputs: generic styles and controls

In alluvial river systems, lateral inputs of water and/or sediment at junctions or undercut hillsides can disrupt what would otherwise be smooth downstream trends in mainstream bed elevation, channel gradient, and bed grain size. Generic styles of mainstream response to lateral inputs are investigated using a one‐dimensional sediment routing model with multiple grain size fractions. Numerical experiments isolate the effects of three para‐meters: ratio of tributary to mainstream water flux (QR), ratio of tributary to mainstream bedload flux (FR), and ratio of tributary to mainstream bedload diameter (DR). The findings are not unduly sensitive to the choice of initial conditions or to approximations made in the model. The primary distinction is between junctions that aggrade, causing local profile convexity with interrupted downstream fining, and junctions that degrade. The immediate effects of aggradation extend further upstream than downstream, whereas degradation is much more subdued and has no upstream impact. Aggradation is typical of coarse inputs (DR > 2), and degradation of fine inputs (DR < 1), but very high ratios of QR to FR also promote degradation. Both aggrading and degrading junctions can lead to a change in mainstream bed grain size well below the junction, with higher ratios of QR to FR producing a coarser distal bed. The effect of a tributary reflects the interplay between additional bed load and additional discharge to transport it. Copyright © 2006 John Wiley & Sons, Ltd.     

The role of floodplains in attenuating contaminated sediment fluxes in formerly mined drainage basins

Many upland river catchments in the UK have been historically mined for metals such as lead (Pb) and zinc (Zn), and as part of the mining process large quantities of metal contaminated sediment were released into the river system. The levels of sediment associated heavy metal contamination in river systems are largely controlled by the volumes of contaminated sediment released into the river and fluvial processes (e.g. erosion and deposition). As a consequence, the contamination patterns are often highly variable, which can make it difficult to create accurate assessments of the volumes of contaminated sediment remaining within the system. This paper uses a combination of techniques to establish the volumes of metal contaminated sediment remaining within the River Swale, UK. Firstly, using detailed field sampling and a geographical information system (GIS), it estimates the volumes of sediment remaining within one formerly mined tributary (Gunnerside Beck) which is then extrapolated to represent the contaminant volumes on other tributaries of the River Swale. Secondly, combining fresh field data with a range of existing data, volumes of contaminated sediment on the main stream of the River Swale are established. This two tier approach shows that significant volumes of contaminated sediment remain within the River Swale, with over 32 000 tonnes of Pb within the mined tributaries and 123 000 tonnes within the main channel belt of the River Swale itself. This represents approximately 28% of the Pb produced in the Swale catchment. Given these volumes and present day rates of removal, it may take over 5000 years for all of the metal rich sediment to be removed from the catchment. If the contaminated sediment is used as a tracer, present day rates of reworking of floodplain sediment can be calculated to be 0·02% per year. Copyright © 2008 John Wiley & Sons, Ltd.     

三峡水库长江干流及其支流枯水期浮游植物多样性与水质

2010年4月对长江干流和26条支流未淹没区与回水区的浮游植物进行调查.结果表明,硅藻、绿藻和蓝藻共占浮游植物种类的93.33%～93.88%.干流优势种类有1门1种、未淹没区有3门6种、回水区有5门6种,出现率分别为15.38%、9.23%和25.00%.回水区现存量平均值最高、未淹没区其次、干流最低.现存量组成在干流、未淹没区和回水区之间有差异,绿藻所占比例干流最高,硅藻所占比例未淹没区最高,隐藻、蓝藻和甲藻所占比例均在回水区最高.Shannon-Wiener多样性指数(H’)和Pielou均匀性指数(J),未淹没区最高、干流次之、回水区最低.17条支流回水区H’和8条支流回水区J均低于未淹没区.水质评价显示,轻或无污染断面(采样点)的比例,干流为76.92%,未淹没区为84.62%,回水区为47.06%.19条(73.08%)支流回水区出现中污染或重污染,7条(26.92%)支流未淹没区出现中污染或重污染.三峡工程蓄水对回水区浮游植物与水质影响比长江干流更大.     

潮汐河口支流建闸闸下淤积研究

潮汐河口建闸的关键问题是闸下淤积。在潮汐河口支流口门上建闸,其闸下淤积面貌主要取决于干流主槽的位置,这与在潮汐河口干流上建闸的闸下淤积问题有着本质上的差异。以钱塘江河口支流曹娥江口门建闸为例,应用河床演变分析、动床实体模型和现场冲淤试验预测了曹娥江大闸闸下淤积面貌和淤积速率,为曹娥江大闸的建设提供了科学依据。     

三峡水库典型支流上游区和回水区营养状态分析

2006年3、5、8月,对三峡水库成库后5条支流的上游区和回水区水质参数及营养因子分布进行了初步研究.研究结果表明,支流高锰酸盐指数范围在1.00-2.50mg/L、COD范围为6.00-26.5mg/L,上游区与回水区有机物含量差异不大,支流目前未受到有机物污染影响.NH_4~+-N范围为0.039-0.367mg/L,各支流含量均为丰水期最大.TN范围在0.58-1.67mg/L,TP范围在0.005-0.133mg/L,支流回水区TN和TP含量均远高于水体发生富营养化的最低限制值,水体存在发生富营养化的风险.大多支流N/P比值处于适宜藻类生长范围.Chl.a浓度范围为0.94-28.9mg/m~3,各支流回水区Chl.a浓度均为5月最大河流回水区Chl.a浓度高于上游区,上游区、回水区Chl.a含量有显著差异.选用修正的Carlson营养状态指数(Trophic State Index)TSI_M法,评价了支流水体营养状态,TSI_M指数范围在36.0-64.2,上游区除龙河、澎溪河5月达到富营养水平外,其余支流均为贫-中营养水平.回水区各支流均达到中-富营养水平.支流回水区营养状态指数均高于上游区,但各支流增加幅度不同.支流回水区水体营养状态明显受三峡水库蓄水水体流速减缓的影响.Chl.a与COD(n=15,P0.01)呈极显著正相关,与其它营养因子无明显相关关系.三峡水库完工后,支流回水区水体流速减缓,富营养化趋势可能加重.     

黄河上游干支流交汇区沙坝淤堵形成条件

针对黄河上游干、支流交汇区形成的沙坝淤堵事件,利用野外观测资料,分析了支流高含沙洪水特性及交汇区沙坝淤堵特点,探讨了汇流比(支流流量与干流流量之比)、支流洪水水量、支流洪水沙量等因素对沙坝淤堵形成的影响;根据动量原理建立了交汇区形成沙坝淤堵的判别关系,结合黄河上游干、支流洪水输移特性,得出了基于汇流比与支流洪水水量关系及支流洪水沙量与支流洪水水量关系的沙坝淤堵判别条件。由此,可根据汇流比、支流洪水水量及沙量判断交汇区能否形成沙坝淤堵,可为暴雨洪水期黄河上游交汇区形成沙坝淤堵灾害的预报及防治提供参考。     

Flow and sediment regimes at tributary junctions on a regulated river: impact on sediment residence time and benthic macroinvertebrate communities

Tributaries may either ameliorate or exacerbate the geomorphic and ecologic impacts of flow regulation by altering the flux of water and sediment into the flow‐regulated mainstem. To capture the effects of tributary influences on a flow regulated river, long‐term discharge and cross‐sectional data are used to assess the geomorphic and hydrologic impacts of impoundment. In addition, the use of the short‐lived cosmogenic radioisotope ⁷Be (half‐life 53·4 days) to link sediment transport dynamics to benthic macroinvertebrate community structure is evaluated. It is found that the ⁷Be activity of transitional bed load sediment is highly seasonal and reflects both variations in activity of sediment sources and limited sediment residence time within the junction. Benthic communities also exhibit a strong seasonal variability. In the spring, neither the ⁷Be activity of the sediment, nor benthic communities exhibit clear relationships with sample site location. In contrast, during the late summer the ratio of Ephemeroptera (mayflies)/Trichoptera (caddisflies) decreased significantly below tributary junctions. This decrease in benthic community ratio was driven by increases in caddisfly abundance and was strongly correlated with the presence of recently ⁷Be tagged transitional bedload sediment. These observations are probably associated with the presence of coarse, stable, and unembedded substrate downstream of tributaries and the rapid turnover of sediment that may also be associated with a rapid flux in nutrients or seston. The results show that tributaries are impacting the flow‐regulated mainstem and that these impacts are reflected in the benthic community structure and in the ⁷Be activity of transitional bed load sediment. Moreover, the observed reduction in competence and capacity of the mainstem following flood control suggests that these spatial discontinuities may be a consequence of impoundment. Copyright © 2008 John Wiley & Sons, Ltd.     

贵州乌江南源上游流域不同岩溶地貌单元的流量衰减分析

选取云南高原向贵州高原过渡地带上的乌江南源——贵州省三岔河上游流域作为研究对象，分别提取其流域内的花渔洞地下河流域与三塘地下河流域的地形指标，分析两者的流量衰减现状，并探讨了岩溶地表形态和岩溶含水介质结构之间的关系。结果显示:（1）花渔洞地下河流域的平均起伏度为73.2 m，可分为高起伏度的Ⅰ区（均值122 m）和低起伏度的Ⅱ区（均值64 m）两个区，其分别占整个流域面积的14.9%和85.1%；三塘地下河流域的平均起伏度为87.6 m，可分为高起伏度的Ⅰ区（均值106 m）、中起伏度的Ⅱ区（均值81 m）和低起伏度的Ⅲ区（均值48 m）三个区，其分别占流域面积的40.2%，49.7%和10.1%；（2）花渔洞地下河流域各阶段的衰减系数为0.000 3，0.000 1，0.000 06（0.5 h）-1，总蓄水量达2 199.356×104 m3，各亚动态蓄水量分别占总蓄水量的0.1%，9.9%、90.0%；三塘地下河流域各阶段的衰减系数为0.001、0.000 3、0.000 1（0.5 h）-1，总蓄水量为2 310.902×104 m3，各亚动态蓄水量分别占总蓄水量的9.4%、30.8%、59.8%。这表明地面起伏度和衰减动态之间可能存在着关联性，即高起伏度对应岩溶发育强烈的管道流，低起伏度对应导水通道较小的裂隙、溶隙等含水层。