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Downstream Areas (downstream + area)

Distribution by Scientific Domains

Earth and Environmental Science	75%

Selected Abstracts

Prediction of the behaviour of landslide dams using a geomorphological dimensionless index

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2003
L. Ermini
Abstract Landslide dams are a common phenomenon. They form when a landslide reaches the bottom of a river valley causing a blockage. The first effect of such a dam is the infilling of a lake that inundates the areas upstream, while the possibility of a sudden dam collapse, with a rapid release of the impounded waters, poses a higher flood risk to the downstream areas. The results of the main inventories carried out to date on landslide dams, have been examined to determine criteria for forecasting landslide dam evolution with particular emphasis on the assessment of dam stability. Not all landslides result in the blockage of a river channel. This only occurs with ones that can move a large amount of material with moderate or high-velocities. In most cases, these landslides are triggered by rainfall events or high magnitude earthquakes. A relationship also exists between the volume of the displaced material and the landslide dam stability. Several authors have proposed that landslide dam behaviour can be forecast by defining various geomorphological indexes, that result from the combination of variables identifying both the dam and the dammed river channel. Further developments of this geomorphological approach are presented in this paper by the definition of a dimensionless blockage index. Starting with an analysis of 84 episodes selected worldwide, it proved to be a useful tool for making accurate predictions concerning the fate of a landslide dam. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Water problems and hydrological research in the Yellow River and the Huai and Hai River basins of China

HYDROLOGICAL PROCESSES, Issue 12 2004
Changming Liu
Abstract This paper deals with hydrological research in regard to the water resources crisis in the vulnerable areas found in the northern part of China. This area includes three main river basins, namely the basins of the Yellow (Huang) River, the Hai River and the Huai River. Several water problems are becoming very severe. Among them, two are the most critical: the Yellow River has been drained dry in the main course of its lower reaches and along its major tributaries, and the groundwater table has rapidly declined in the floodplains of the three rivers' downstream areas. To counter the problems, particularly the critical issues mentioned above, hydrological research, which serves as the basis of water development and management, has been carried out in the last two decades. This paper addresses three basic scientific problems in North China, namely: (a) water consumption and the capacity for saving water; (b) the changes in hydrological processes and water resources caused by natural change and human activities; and (c) the ability to supply water resources and water safety in terms of both quantity and quality within a changing environment. However, opportunities and challenges for ameliorating the problems exist, and new ideas and methodology to solve the problems have been proposed, such as the interface process study on the interactions in the soil,root interface, the plant,atmosphere interface, the soil,atmosphere interface, and the interface of soil water and groundwater. In order to manage water resources in a sustainable manner, the study of water resources' renewal ability as affected by natural change and human activity is addressed from the viewpoint of both water quantity and quality, and their integration. To reduce the vulnerability of water resources in regional water management, a paradigm of sustainable water resources utilization is also proposed, using water,heat balance, water,salt balance, water,sediment balance, and water supply,demand balance. This approach may help reveal the basic problems and point to possible approaches to solving the water problems in North China in the 21st century. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Improving public information about large hydroelectric dams: Case studies in France and West Africa

NATURAL RESOURCES FORUM, Issue 1 2003
Armelle Faure
It is becoming more common for public authorities in charge of dam construction and management to inform the population living in the area soon to be submerged by a proposed dam. However, populations living further downstream along a river to be dammed, have often been left to find out by chance, despite the fact that the changes to the river flow regime will have an important impact on their lives, sometimes serious negative impacts. This article makes a comparison between two dams, one at Bort-les-Orgues across the upper Dordogne River in southern France, the other the Bagré Dam over the Nakambé (or White Volta) River in south-eastern Burkina Faso. The article discusses dam construction and operation from the point of view of the concerned populations living in the reservoir and downstream areas. In 2000, a study was carried out in the Dordogne Valley to ascertain downstream impacts of dam operations and information needs of the population. Suggestions from local river users related mostly to improving public information about predicted and actual flow rates and actual flow in real time along the 300 km course of the Dordogne between the dams and the estuary. Such information should be disseminated as widely as possible through available media, including the Internet, and also displayed visibly in key locations along the length of the river. [source]

The value of observations.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 628 2007
II: The value of observations located in singular-vector-based target areas
Abstract Data-assimilation experiments have been run in seven different configurations for two seasons to assess the value of observations taken in target regions identified either using singular vectors (SVs) or randomly, and located over the Pacific or the Atlantic Oceans. The value has been measured by the relative short-range forecast error reduction in downstream areas, specifically a North American region for observations taken in the Pacific Ocean, and a European region for observations taken in the Atlantic Ocean. Overall, results have indicated (1) that observations taken in SV-target areas are on average more valuable than observations taken in randomly selected areas, (2) that it is important that the daily set of singular vectors are used to compute the target areas, and (3) that the value of targeted observations depends on the region, the season and the baseline observing system. If the baseline observing system is data-void over the ocean, then the average value of observations taken in SV-target areas is very high. Considering for example winter 2004, SV-targeted observations over the Pacific (Atlantic) reduce the day-2 forecasts error of 500 hPa geopotential height forecasts in the verification region by 27.5% (19.1%), compared to 15.7% (14.9%) for observations taken in random areas. By contrast, if the baseline observing system is data-rich over the ocean, then the average value of observations taken in SV-target areas is rather small. Considering for example winter 2004, it has been estimated that adding SV-targeted observations over the Pacific (Atlantic) would reduce, on average, the day-2 forecasts error in the verification region by 4.0% (2.0%), compared to 0.5% (1.7%) for observations in random areas. These average results have been confirmed by single-case investigations, and by a careful examination of time series of forecast errors. These results indicate that more accurate assimilation systems that can exploit the potential value of localized observations are needed to increase the average return of investments in targeting field experiments. Copyright © 2007 Royal Meteorological Society [source]