CHANNEL STABILITY DOWNSTREAM FROM A DAM ASSESSED USING AERIAL PHOTOGRAPHS AND STREAM‐GAGE INFORMATION1

ABSTRACT: The stability of the Neosho River channel downstream from John Redmond Dam, in southeast Kansas, was investigated using multiple‐date aerial photographs and stream‐gage information. Bankfull channel width was used as the primary indicator variable to assess pre‐ and post‐dam channel change. Five sin‐mile river reaches and four stream gages were used in the analysis. Results indicated that, aside from some localized channel widening, the overall channel change has been minor with little post‐dam change in bankfull channel width. The lack of a pronounced post‐dam channel change may be attributed to a substantial reduction in the magnitude of the post‐dam annual peak discharges in combination with the resistance to erosion of the bed and bank materials. Also, the channel may have been overwidened by a series of large floods that predated construction of the dam, including one with an estimated 500‐year recurrence interval.     

尾矿坝沉积结构特征与性能演化规律研究进展

为了进一步分析尾矿坝沉积结构特征与性能演化规律,本文综述国内外尾矿沉积规律、物理力学特性、服役性能演化规律及溃坝评价方法等有关尾矿坝安全稳定评价的研究现状,指出当前研究存在的不足.在尾矿库沉积规律的研究中,由于模型试验的流槽尺寸有限、边界效应较强,放矿条件不同,对尾矿沉积分布尚未得出一致性规律.而针对多种因素影响下的尾...     

Deteriorated watersheds can be restored: A case study

A project in west-central Colorado demonstrated that a watershed dissected by a dense gully network can be stabilized and rehabilitated. Check dam systems, aided by improved vegetative cover through reduced cattle grazing and plantings, stabilized not only the structurally treated gullies, but also gullies within the network that were not structurally treated. Comparison with untreated gullies located outside of the project area, showed that the outside gullies widened three times as much as the structurally untreated inside gullies. Statistical analysis indicated that precipitation was normal during the treatment and evaluation period.Check dams decreased gully depth by accumulating sediment deposits. In turn, gully bank stabilization was hastened and alluvial aquifer volumes increased. This increase, plus higher infiltration rates as a result of denser vegetation, led to renewed perennial streamflow after 7 treatment years.Within 11 years after treatment, check dam systems and improved vegetation reduced sediment loads in the flows by more than 90 percent, providing a substantial benefit to farmlands and ponds downstream.From this work we are able to conclude that only part of a gully network requires structural treatment. The mainstem gully, and those tributaries controlling the local base levels of others, are the critical segments that should be structurally treated.     

TWO-DIMENSIONAL DIFFUSION-PROBABILISTIC MODEL OF A SLOW DAM BREAK1

ABSTRACT: A two-dimensional model of a dam-break flood wave is developed by simplifying the St. Venant equations to eliminate local acceleration and inertial terms and combining the simplified equations with continuity to form a diffusion type partial differential equation. This model is cascaded with a two point probability estimate scheme to account for uncertainty in the dam break flood hydrograph and channel roughness. The development and application of the probabilistic model is the main contribution of this paper. The approach is applied to a hypothetical dam break of Long Valley Dam on the Owens River above Bishop, California.     

无铰拱形泥石流拦挡坝研究

在泥石流防治工程中，拦挡坝是应用得比较广泛的一种措施。利用土木建筑中的拱结构形式，结合锚杆技术，引入了无铰拱形拦挡坝的概念。在狭窄河谷中，采用无铰拱形坝既可以改善坝体的工作环境，提高其承载能力，又可以减少材料用量，从而降低造价。针对无铰拱形坝的受力特性，进行了分析，提出了加强坝体、实现无铰的构造措施。     

REASSEMBLING HETCH HETCHY: WATER SUPPLY WITHOUT O'SHAUGHNESSY DAM1

The Hetch Hetchy System provides San Francisco with most of its water supply. O'Shaughnessy Dam is one component of this system, providing approximately 25 percent of water storage for the Hetch Hetchy System and none of its conveyance. Removing O'Shaughnessy Dam has gained interest for restoring Hetch Hetchy Valley. The water supply feasibility of removing O'Shaughnessy Dam is analyzed by examining alternative water storage and delivery operations for San Francisco using an economic engineering optimization model. This model ignores institutional and political constraints and has perfect hydrologic foresight to explore water supply possibilities through reoperation of other existing reservoirs. The economic benefits of O'Shaughnessy Dam and its alternatives are measured in terms of the quantity of water supplied to San Francisco and agricultural water users, water treatment costs, and hydropower generation. Results suggest there could be little water scarcity if O'Shaughnessy Dam were to be removed, although removal would be costly due to additional water treatment costs and lost hydropower generation.     

A HYDRAULIC TRANSIENT MODEL OF THE UPPER ST. LAWRENCE RIVER FOR WATER RESOURCES STUDIES1

ABSTRACT: A one-dimensional hydraulic transient model has been designed for water resource studies of Lake Ontario and the Upper St. Lawrence River. The model simulates water surface profiles and flows in the St. Lawrence River between Lake Ontario and the Moses-Saunders Power Dam under both open water and ice-covered conditions. Errors in water surface elevations were found to be less than 0.2 feet during quasi-steady conditions on the river. Comparable errors occurred during the ice-covered conditions. A sensitivity analysis found the model to be most sensitive to the roughness coefficients and the flow through the power dam.     

AN INTEGRATIVE APPROACH TOWARDS UNDERSTANDING ECOLOGICAL RESPONSES TO DAM REMOVAL: THE MANATAWNY CREEK STUDY1

ABSTRACT: Dam removal has been proposed as an effective method of river restoration, but few integrative studies have examined ecological responses to the removal of dams. In 1999, we initiated an interdisciplinary study to determine ecological responses to the removal of a 2 m high dam on lower Manatawny Creek in southeastern Pennsylvania. We used an integrative monitoring program to assess the physical, chemical, and biological responses to dam removal. Following removal in 2000, increased sediment transport has led to major changes in channel form in the former impoundment and downstream reaches. Water quality did not change markedly following removal, probably because of the impoundment's short hydraulic residence time (less than two hours at base flow) and infrequent temperature stratification. When the impoundment was converted to a free flowing reach, the composition of the benthic macroinvertebrate and fish assemblages in this portion of Manatawny Creek shifted dramatically from lentic to lotic taxa. Some fish species inhabiting the free flowing reach downstream from the dam were negatively affected by large scale sediment transport and habitat alteration following dam removal, but this appears to be a short term response. Based on our observations and experiences in this study, we provide a list of issues to evaluate when considering future dam removals.     

瑞士大坝应急管理特点及其对中国的启示

中国水库大坝应急管理存在应急管理责任体系不清晰,应急预案操作性差,预警设施不完备等突出问题,严重影响大坝应急管理。从应急体制、硬件设施、应急机制、应急预案等方面对比中国和瑞士两国大坝应急管理做法,找到了可供中国借鉴的瑞士经验,认为应当明确政府和水库管理单位在大坝应急管理中的职责划分,简化预案表达方式,加强预案审查审批,完善预警设施,加强宣传演练。     

尾矿库初期坝稳定性的合成孔径雷达干涉变形检测与流固耦合数值模拟分析

某尾矿库初期坝采用分段施工,可能产生不均匀沉降,影响坝体的稳定性。采用孔径雷达干涉技术对尾矿库初期坝进行了短期变形速率观测,得出坝体右侧的后期填筑区域整体上与主体仍能够基本保持同步沉降。建立了三维流固耦合模型,分析了尾矿库初期坝的静力稳定性和渗流稳定性,结果表明:初期坝体的水平位移和竖向位移都在安全范围之内,考虑水和尾砂的共同作用,后期堆积坝堆积至1765m高程时,坝体顶部和后期回填区域,存在小量位移变形,静态稳定性安全系数达到2.25,初期坝能够保持稳定。