The Hydrologic Importance of Small- and Medium-Sized Dams: Examples from Texas

Studies of the effects of dams have emphasized large and very large dams; less well understood are the impacts caused by smaller dams. Using Texas as an example area, this article highlights the role of small- and medium-sized dams in affecting the surface hydrology of river systems. Analysis of data from the National Inventory of Dams (NID) in a geographic information system showed that small and medium dams comprise about 97 percent of the dams registered in Texas. A small-or medium-sized dam is found approximately every 100 km² of area and about 120 km of river length. Different from large dams, which affect water storage the most, the major impact of these smaller dams is fragmentation of river landscapes. Analysis of data for dams extracted from digital orthoquads and for water bodies from the National Hydrography Dataset indicates that the extent of river fragmentation is likely greater than that suggested by data from the NID, because the NID underrepresents the smaller dams. Such extent of river fragmentation can degrade stream habitats and pose barriers to the migration of aquatic species and transport of sediment. Because small and medium dams are largely built for fire protection and stock ponds, mitigating the impacts associated with these dams likely involves working with the private individuals who own them.     

The geographic distribution of small dams in Oregon using ecoregion and landform classification

Abstract

Small dams fragment river landscapes, disrupting channel connectivity and impacting water quality and quantity. Although they impound volumetrically less total water than large dams, the ubiquity of small dams suggests their cumulative impacts could be significant. Documenting the distribution and characteristics of small dams is necessary to understanding and mitigating their impacts. In this study, we compare datasets of small dams in Oregon, compile a new comprehensive dataset, and document geographic variations in small dam distributions between different ecoregions. We used Oregon Water Resources Department dam and Oregon Department of Fish and Wildlife fish passage barrier datasets to compare dam heights and contributing drainage areas between different ecoregions. Over 61% of Oregon’s land area is above one or more small dam. We highlight the location of Oregon’s small dams at valley margins, transition zones between flat plains and mountains, and areas of high population density. Given the hidden nature of small dams, evaluation of small dam impacts using public imagery is not effective. However, knowledge of small dam distributions given their association with landforms can aid in finding unrecorded dams, assessing approaches for evaluating their geomorphic impacts, and informing their management.     

Geomorphic hazard assessment of landslide dams in South Westland, New Zealand: fundamental problems and approaches

Quantitative assessments of landslide hazard usually employ empirical, heuristic, deterministic, or statistical methods to derive estimates of magnitude–frequency distributions of landsliding. The formation and failure of landslide dams are common geomorphic processes in mountain regions throughout the world, causing a series of consequential off-site hazards such as catastrophic outburst floods, debris flows, backwater ponding, up- and downstream aggradation, and channel instability.Conceptual and methodological problems of quantifying geomorphic hazard from landslide dams result from (a) aspects of defining “landslide-dam magnitude”, (b) scaling effects, i.e. the geomorphic long-range and long-term implications of river blockage, and (c) paucity of empirical data. Geomorphic hazard from a landslide dam-break flood on the basis of conditional probabilities is being analysed for the alpine South Westland region of New Zealand, where formation and failure of landslide dams is frequent. Quantification of the annual probability of landsliding and subsequent dam formation in the area is limited by historical and only partially representative empirical data on slope instability. Since landslide-dam stability is a major control governing the potential of catastrophic outburst flooding, the ensuing hazard is best assessed on a recurring basis. GIS-based modelling of virtual landslide dams is a simple and cost-effective approach to approximate site-specific landslide dam and lake dimensions, reservoir infill times, and scaled magnitude of potential outburst floods. Although crude, these order-of-magnitude results provide information critical to natural hazard planning, mitigation, or emergency management decisions.     

成昆铁路泥石流防治工程运行效果浅析

概述了成昆铁路沿线泥石流防治工程基本情况及此次调研工点简况．对调研工点所建工程的运行效果进行了较系统的分析，对各类工程的主要技术参数进行了讨论，并在此基础上提出了改善工程防灾效能的若干对策．这对今后泥石流防治有很现实的意义．     

无定河流域产沙量变化的淤地坝效应分析

无定河流域1971~1989年的年均流量、悬移质含沙量及输沙率比1954~1970年的明显变小,而月均水沙过程曲线也发生了明显变化。上述水沙过程的变化受到1970年以来人类活动的强烈影响,而淤地坝建设是主因。为探讨淤地坝的减沙效应,提出淤地坝有效减沙面积这一概念,并拟合了动态变化的淤地坝有效减沙面积与年份之间的关系,发现该关系曲线与无定河流域各年代产沙量的变化情况相符。自1990年以来无定河流域淤地坝有效减沙面积呈明显递减趋势,导致了自上世纪90年代以来该流域的产沙量出现增大现象。为了抑制该流域的产沙量,势必需要加大淤地坝建设的力度。如果想使该流域的产沙量逐渐减少,则至少要使流域内年淤地坝有效减沙面积逐年增加。     

Modeling River Connectivity Using the Barrier Assessment Tool and Available Data on Registered Dams in the Guadalupe–San Antonio River System,Texas

The rate of dam building has declined in the United States, but dam building is still considered an integral part of water supply management, particularly in arid and semiarid regions. Understanding how dams affect river connectivity is a key component of river basin management. This study analyzed the spatial and temporal patterns of fragmentation in the Guadalupe–San Antonio River System (GSARS) and how these patterns were related to dam size, age, and purpose. Using a shapefile of registered dams and the National Hydrography Dataset High Resolution (NHD-HR) as input data for the Barrier Assessment Tool (BAT), six successive connectivity models were created. The average length of functional river networks (FRNs) decreased over time but the number of FRNs over 100?km stayed relatively stable. Fragmentation in the GSARS was concentrated around urban centers, and the majority of fragmentation occurred gradually as dams separated small FRNs along tributaries and headwaters. This gradual decline in longitudinal connectivity was punctuated by sporadically large separations of river networks by particular dams based on their location and time of commissioning. The methodology presented here provides a way to analyze both the extent and the temporal evolution of fragmentation in a river system. Key Words: Barrier Assessment Tool (BAT), fragmentation, functional river networks, river connectivity.     

Medium and small embankment dams on permafrost: A discussion of current concepts

This article discusses the current concepts of dam design and construction in permafrost regions. It is demonstrated that embankment dams often change their state from frozen to thawed and back during the operation period. It is shown that these transitions are not always attributable to observed climate warming. Where geotechnical, hydrogeological, and permafrost conditions are complicated, proper performance of embankment dams can only be provided by adhering to a selected thermal design for, as an example, a frozen state.     

陕西榆林地区无定河流域淤地坝遥感解译

淤地坝是黄土高原水土流失防治的主要措施之一,明确淤地坝的分布、规模等重要参数信息对流域水土保持研究具有重要意义。利用遥感技术（RS）和地理信息系统（GIS）技术,结合陕北地区无定河流域高分二号卫星影像、野外踏勘及资料收集到的研究区淤地坝情况,对其进行预处理获取矢量数据,通过对比分析,得到淤地坝解译标志。针对榆林地区无定河流域淤地坝进行遥感解译,利用遥感及GIS软件实现淤地坝数目、淤地坝位置、水面面积、控制面积等主要信息的提取,获取淤地坝在定边、靖边、米脂、绥德、横山、榆阳、子洲和清涧8个县（区）分布状况。结果显示：研究区共解译出疑似淤地坝图斑1257个,其中榆阳区60个,横山区85个,定边县65个,靖边县19个,米脂县470个,子州县99个,绥德县316个,清涧县143个。由此发现,淤地坝主要分布于无定河下游区域的绥德、米脂、子洲和清涧4县的沟道内,且沟道内多存在耕地或水域。将淤地坝分布情况与地形、年均降雨量、农业种植面积和地质灾害等进行比较分析,显示其分布状况与这些因素相关联,表现为沟壑纵横的区域淤地坝较多,农业种植面积较少的区域淤地坝较多,年均降雨量和耕种面积比值较大区域淤地坝较多。由此,总结其分布规律,为未来淤地坝的维护和修建提供重要支持。     

Discriminant analysis of the geomorphic characteristics and stability of landslide dams

Landslides can cause the formation of dams, but these dams often fail soon after lake formation. Thus, rapidly evaluating the stability of a landslide dam is crucial for effective hazard mitigation. This study utilizes discriminant analysis based on a Japanese dataset consisting of 43 well documented landslide dams to determine the significant variables, including log-transformed peak flow (or catchment area), and log-transformed dam height, width and length in hierarchical order, which affect the stability of a landslide dam. The high overall prediction power (88.4% of the 43 training cases are correctly classified) and the high cross-validation accuracy (86%) demonstrate the robustness of the proposed discriminant models PHWL (with variables including log-transformed peak flow, and log-transformed dam height, width and length) and AHWL (with variables including log-transformed catchment area, and log-transformed dam height, width and length). Compared to a previously proposed “DBI” index-based graphic approach, the discriminant model AHV – which uses the log-transformed catchment area, dam height, and dam volume as relevant variables – shows better ability to evaluate the stability of landslide dams. Although these discriminant models are established using a Japanese dataset only, the present multivariate statistical approach can be applied for an expanded dataset without any difficulty when more completely documented worldwide landslide-dam data are available.     

Cyclic behavior of soils and numerical analyses in cold regions and seismic zones

The solutions of boundary value problems involving strain-softening material property contain serious difficulties from both modeling of strain-localization and a viewpoint of numerical procedure. Mesh size-dependent hardening modulus is considered to alleviate the mesh size-dependency of the solution. The elasto-plastic soil model with kinematic hardening model considering the cumulative deformation by cyclic loading is developed. In finite element analyses, the dynamic relaxation method combined with the generalized return-mapping algorithm is applied to the static drained and un-drained tri-axial tests and plane strain tests. The cyclic behavior of retaining wall problems by freeze and thaw in cold regions is also analyzed. Finally the dynamic progressive failure analysis of rockfill dam is carried out.     

Water resource management in the USA: a case study of large dams

The construction of large dams in the USA reveals a rapid growth in activity in the post-Second World War period, with the largest number of dams being inaugurated in the mid-1960s. Texas, with 823 dams, is the state with the largest number, followed in turn by California, Oklahoma, Pennsylvania and Colorado. At the other extreme some states have fewer than a dozen dams. Although there are large variations in the number of dams between states nearly all of them record peak constructional activity between the late 1950s and early 1970s. Surprisingly, most dams have relatively small reservoirs with about 70 per cent of the total having capacities of less than 10⁶ m³. Over two-thirds of all dams have been constructed with a single aim in view, with flood control being the most important reason. Only 1.5 per cent of all dams are utilized for four or more purposes. The objectives behind dam construction reveal changes since the 19th century. In the early years of the 20th century irrigation, hydro-electric power generation and water supply were the most important reasons for dam construction, whereas in the post-1950 period flood control stands out as the dominant activity. Changing technology, the introduction of specific legislation and changing attitudes to the environment have been the major influences on dam-building activity over the period studied.     

影响淤地坝建设的地理要素——以黄河中游多沙粗沙区为例

采用定性分析和定量计算、微观机理研究和宏观分析相结合的方法,对影响淤地坝建设的地理要素进行筛选,重点分析了沟壑密度、土壤侵蚀模数、农业人口密度对小流域淤地坝建设,主要是对淤地坝空间布局的影响;以黄河中游多沙粗沙区为研究对象,根据研究区域45个县(旗、市)的沟壑密度、土壤侵蚀模数、农业人口密度和淤地坝密度的基础数据,从地理学角度系统分析它们和研究区域淤地坝密度的关系,研究影响该区域淤地坝建设及布局的主要地理要素。结果表明,在黄河中游多沙粗沙区,影响淤地坝建设最主要的地理要素是农业人口密度,即人类活动的剧烈程度和淤地坝密度之间存在着直接的关系,分析结果为黄河中游多沙粗沙区淤地坝建设提供了科学依据。     

电站建设对澜沧江-湄公河泥沙年内分配的影响

采用澜沧江漫湾电站上游旧州站和下游允景洪、清盛站1987~2003 年逐月悬移质泥沙含量实测资料, 分析对比了三站年内泥沙分配不均匀系数、集中度和集中期、变化幅度等特性。将上述参数与澜沧江上游干流漫湾与大朝山电站建设的响应进行关联研究, 分析电站建设进程对河道输沙变化的驱动作用。结果表明: (1) 旧州水文站泥沙年内分配与区域气候变化 (降水) 趋势一致, 研究时段内不均匀性系数呈上升趋势, 维持天然河道输沙特性; 允景洪和 清盛水文站的泥沙年内分配不均匀性系数对电站建设等人类活动的响应程度不一致, 允景洪站泥沙含量不均匀系数先减小后急剧增加, 而清盛站呈微弱减小态势。(2) 旧州水文站泥沙年 内分配集中度及集中期基本无变化; 允景洪与清盛水文站的泥沙年内分配集中度变化较大, 泥沙集中期在在电站施工的高峰期(1987~1992 年、1997~2003 年) 后延, 且不同步, 允景洪在漫湾施工期后延5~6 天, 而清盛则后延将近半个月,而在大朝山施工期, 允景洪的后延响应 却明显于清盛。(3) 旧州站相对、绝对泥沙变幅逐时段递增, 允景洪站年内最大与最小月泥沙含量的相对、绝对变化幅度均减小, 清盛站泥沙含量的相对变化幅度却先增后减, 绝对变化 幅度则一直减小。三站泥沙年内极值变幅以及电站建设前后的响应差异, 说明三站泥沙变化的驱动因子有明显不同。这些关于泥沙含量年内分配特征规律的发现, 为研究澜沧江干流电站建设对上下游泥沙变化以及跨境影响的科学评价提供了新的佐证。     

EFFECT OF DAMS ON MOUNTAINOUS BEDROCK RIVERS

This study examines the adjustment of river systems in the Golan Heights to reservoir construction in small basaltic mountainous catchments where total water flow is impounded, and discusses comparisons with the effects of large dams on alluvial rivers. Annual rainfall ranges from 500 mm to 900 mm, and no major springs are found in the area. About 3/4 of total runoff is in the form of floods caused by rainstorms. The 11 dams receive drainage from about 20% of the total catchment, and a third of the total runoff. Changes in the river channels were studied at 28 field stations. Flood marks provided peak stage levels for largest season discharge, and 8 nearby hydrometric stations provided a continuous hydrological record. Bed material was sampled at each cross-section site. The main effect of river impoundment is a sharp decrease in flood peaks below the reservoirs to about one-third of their previous natural regime. The channel cross-sectional area decreased, but no temporal adjustment can be established, as most of the reservoirs were built in the last 5–8 years. Channel-flow hydraulics are competent enough to transport the suspended material, but evidence of aggradation was found in the channel reaches close to the dams. Bedload transport and the size of transported cobbles and boulders decreased downstream from the dams. Increased vegetation cover downstream from the dams was the most pronounced effect. Adjustment of the fluvial system to dam building in mountainous streams seems to be less sensitive than in alluvial channels. [Key words: fluvial geomorphology, dams, water reservoirs, environmental changes, Israel.]     

A preliminary study on the element strata and palaeoenvironment of core NP95 1 from the Prydz Bay,Antarctica

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西藏东南部泥石流堵塞坝的形成机理

西藏东南部山高谷深,冰川发育,冰碛等松散堆积物厚度大,经常发生大型或特大型泥石流堵断主河,形成堵塞坝。针对西藏东南部4条典型泥石流沟所发生的7次大型或特大型泥石流中,有5次形成堵塞坝,来剖析泥石流堵塞坝形成的机理和主要因素,提出由于冰雪崩、冰湖溃决或大规模滑坡活动,所激发的首阵或前几阵大流量、高速度、多巨砾,并与主河正交的粘性泥石流,最容易形成堵塞坝。     

南极普里兹湾NP951柱样元素地层与古环境初步研究

对南极普里兹湾ＮＰ９５１柱样的元素地球化学特征及其古环境意义进行了研究。结果表明，本区沉积物在沉积过程中受冰盖消融、淡水涌入和陆源物质的影响较大；沉积物中ＳｉＯ２、Ａｌ２Ｏ３、Ｆｅ２Ｏ３、ＣａＯ、ＭｇＯ、Ｐ、Ｓ、Ｃｏｒｇ等元素组分较好地记录了由古气候变化而引起的物源改变，这些元素组分在地层中的分布规律与古海洋沉积环境及古气候变迁相一致；自晚更新世末期以来的气候大致可分为温暖期、寒冷期、高温期、转冷期和转暖期五个区段；在柱样的１４５ｃｍ（１４．４ｋａＢ．Ｐ．）、８５ｃｍ（１０．３ｋａＢ．Ｐ．）和２５ｃｍ（６．３ｋａＢ．Ｐ．）处出现了古气温的高值点，指示了气候的变化；８５ｃｍ处元素含量的突变指示了异常事件的发生，该层位正好对应于哥德堡地球磁场漂移，全球气温突然变暖，标志着１０．３ｋａＢ．Ｐ．以后南极地区进入了全新世。     

基于多源数据的皇甫川淤地坝信息提取

淤地坝是黄土高原水土流失防治的主要工程措施之一,明确淤地坝重要参数信息对流域水土保持研究具有重要意义。利用皇甫川流域不同数据来源资料包括地形图（1976年）、TM影像（1990年、2007年）、Google Earth影像（2010年）对其进行预处理获取矢量数据,利用遥感及GIS软件实现淤地坝数目、淤地坝位置、水面面积、控制面积等主要信息的提取并分析其动态变化,采用相关系数、NDAI和DAI进行提取误差评定。结果表明：皇甫川流域淤地坝数目随年代递增而增加,水面面积和控制面积也随之增大,流域西部淤地坝数目明显少于东部。TM数据上提取的淤地坝水面面积与通过Google Earth数据提取的结果相关系数为0.98,实测淤地坝控制面积与TM影像上提取结果相关系数为0.96,NDAI和DAI值平均误差绝对值均<5%。由此得出,基于多源数据淤地坝信息提取技术具有很好的可行性及较高的准确性,本文为淤地坝减水减沙效益及黄河粗泥沙来源研究提供必要的决策支持。     

Downstream effects of dams on livelihoods of river-dependent communities: the case of Ghana’s Kpong Dam

Construction of dams affects the livelihoods of the population living along the dammed river. There is a need for more studies to guide dam development policies and management to safeguard the livelihoods of local river users. This paper examines the effects of dams on the socio-economic livelihoods of downstream communities by drawing on the Kpong Dam in Ghana constructed from 1979 to 1982 with the goal of supplying energy and for irrigation purposes. Primary data were collected in resettled and non-resettled downstream communities using a mixed-research approach. This case study highlights how the Kpong Dam has affected the downstream river-dependent population whose livelihoods, particularly farming and fishing revolved around the seasonal flow regimes of the Volta River. Our study challenges the general perception that dams increase agricultural production by illustrating that developing ancillary facilities such as irrigation schemes as part of dam projects can enhance all-year-round agricultural production to improve food and income security of downstream households only when constraints such as lack of farm inputs are addressed. To safeguard livelihoods and limit the social impacts of dams, compensation schemes and alternative livelihood activities should be designed to include resettled and non-resettled communities along the downstream areas affected by dam projects.     

峡谷区域水电开发景观影响评价——以怒江为例

水电开发的环境影响评价近年来日益受到重视。景观影响评价是一个重要的内容。在简要 阐述水电开发的景观影响评价的相关概念及意义之后,首先阐述了峡谷区域水电开发的景观影 响及评价方法,然后以怒江为例, 具体探讨了峡谷区域水电开发景观影响评价的过程与结果。通 过设计一系列景观测度参数,包括可视域损失、大坝视觉影响范围、高差损失、景点改变、峡谷急 流损失等, 并利用GIS 进行模拟,基于计算结果对水电建设对峡谷整体和局部景观影响以及坝址 各段建库适宜性进行了评价。最后指出, 在怒江这样的急流高山峡谷上建坝应该慎而又慎, 其决 策应参考包含景观影响评价在内的环境影响评价, 并应逐步完善此方面的立法。