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Large Dams (large + dam)
Selected AbstractsDAM-INDUCED MODIFICATIONS TO UPPER ALLEGHENY RIVER STREAMFLOW PATTERNS AND THEIR BIODIVERSITY IMPLICATIONS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2002C. Mark Cowell ABSTRACT: This study evaluates the streamflow characteristics of the upper Allegheny River during the periods preceding (1936 to 1965) and following (1966 to 1997) completion of the Kinzua Dam in northwestern Pennsylvania. Inter-period trends in seasonal patterns of discharge and peak flow at three downstream sites are compared to those at two upstream sites to determine the influence of this large dam on surface water hydrology. Climatic records indicate that significant changes in annual total and seasonal precipitation occurred over the twentieth century. Increased runoff during the late summer through early winter led to increased discharge both upstream and downstream during these months, while slightly less early-year rainfall produced minor reductions in spring flood peaks since 1966. The Kinzua Dam significantly enhanced these trends downstream, creating large reductions in peak flow, while greatly augmenting low flow during the growing season. This reduction in streamflow variability, coupled with other dam-induced changes, has important biodiversity implications. The downstream riparian zone contains numerous threatened/endangered species, many of which are sensitive to the type of habitat modifications produced by the dam. Flood dynamics under the current post-dam conditions are likely to compound the difficulties of maintaining their long-term viability. [source] The impact of catastrophic channel change on freshwater mussels in the Hunter River system, Australia: a conservation assessmentAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2010Hugh A. Jones Abstract 1.Australia has a distinct suite of endemic freshwater mussel species, several of which are restricted to south-eastern Australia, an intensively modified region supporting much of the nation's population and where pressures on freshwater ecosystems are increasing. 2.Surveys were made of 78 sites in the Hunter River system to determine the distribution and abundance of the six mussel species occurring in the region, to identify threatening processes and to locate populations of high conservation value. 3.Mussel populations were mainly distributed in the hydrologically stable southern Barrington rivers, where those in the Williams River have the highest conservation value. Strongholds for Hyridella drapeta were found in Wollombi Brook. 4.Mussels were not detected at 40% of the sites, some of which supported mussels in the past. These were mainly reaches that have undergone river metamorphosis. 5.Where found, most mussel populations had low densities and were highly fragmented. Major threats to these remnant populations are degradation of riparian and instream condition from agricultural activities, extreme climatic events (flood and drought) and the introduced macrophyte, Salvinia molesta. 6.While threat mitigation can be achieved by habitat protection and strategies to reconnect mussel populations, managers are largely unaware of this invertebrate group. Formal recognition of regionally threatened mussel populations would do much to focus efforts on conservation. 7.The proposed construction of a large dam on the Williams River is a potential threat to the most important mussel populations in the Hunter River system. Copyright © 2009 John Wiley & Sons, Ltd. [source] Sediment transport in a highly regulated fluvial system during two consecutive floods (lower Ebro River, NE Iberian Peninsula)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2005Damia Vericat Abstract The transfer of sediment through a highly regulated large fluvial system (lower Ebro River) was analysed during two consecutive floods by means of sediment sampling. Suspended sediment and bedload transport were measured upstream and downstream of large reservoirs. The dams substantially altered flood timing, particularly the peaks, which were advanced downstream from the dams for flood control purposes. The suspended sediment yield upstream from the dams was 1 700 000 tonnes, which represented nearly 99 per cent of the total solid yield. The mean concentrations were close to 0·5 g l,1. The sediment yield downstream from the dams was an order of magnitude lower (173 000 tonnes), showing a mean concentration of 0·05 g l,1. The dams captured up to 95 per cent of the fine sediment carried in suspension in the river channel, preventing it from reaching the lowermost reaches of the river and the delta plain. Total bedload transport upstream from the dams was estimated to be about 25 000 tonnes, only 1·5 per cent of the total load. The median bedload rate was 100 gms,1. Below the dams, the river carried 178 000 tonnes, around 51 per cent of the total load, at a mean rate of 250 g ms,1. The results of sediment transport upstream and downstream from the large dams illustrate the magnitude of the sediment deficit in the lower Ebro River. The river mobilized a total of 350 000 tonnes in the downstream reaches, which were not replaced by sediment from upstream. Therefore, sediment was necessarily entrained from the riverbed and channel banks, causing a mean incision of 33 mm over the 27 km long study reach, altogether a significant step towards the long-term degradation of the lower Ebro River. Copyright © 2005 John Wiley & Sons, Ltd. [source] Threatened obligatory riverine fishes in human-modified Polish riversECOLOGY OF FRESHWATER FISH, Issue 1-2 2000T. Penczak Abstract , The fate of obligatory riverine fish species (rheophils), which are the objects of anglers' exploitation (chub ,Leuciscus cephalus, nase ,Chondrostoma nasus, barbel ,Barbus barbus, gudgeon ,Gobio gobio), and brown trout (Salmo trutta m. fario) and grayling (Thymallus thymallus) (in the Gwda River basin only), were investigated in large alluvial rivers (Pilica and Warta) and in the medium-sized Gwda River basin. The Pilica (1973) and the Warta (1986,1987) were divided by large dams without fish ladders in their middle courses. The Gwda River was divided by only a few dams along its course, but its tributaries carrying pure water had numerous small dams that supplied water for fish farms. Other stresses influencing fish populations in these rivers were: pollution, overfishing, hydroelectric plants and bank revetments. Because the listed stresses occurred alternately and at various periods of time in these rivers, this enabled attributing the cause for extinction and reduction of the abundance and distribution. In the salmon Gwda River basin, a drastic decrease in spatial distribution and reduction of occurrence ranges of brown trout, grayling and barbel was evident in respect to the first study period (1980s) in the 1990s. In the large, alluvial Pilica River, nase, barbel and dace are on the edge of extinction and chub and gudgeon are vulnerable. In the Warta's tailwater, barbel is an extinct species, and chub, dace and gudgeon are vulnerable ones. In a site in the backwater, none of the above mentioned species became extinct, but their abundance and occurrence frequency decreased a bit in respect to the pre-impoundment period. Roach-generalist, which was used in this research as a "control" species, increased in abundance in all 3 rivers. These investigations univocally proved that the dams cause catastrophic stress for obligatory riverine species., [source] World Commission on Dams: implications for food and irrigation1,IRRIGATION AND DRAINAGE, Issue 2 2001Chris Perry barrages; l'irrigation; securité d'alimentation Abstract The World Commission on Dams has now published its report. Insights into the workings and conclusions of the Commission were published in the last edition of this Journal. While the WCD report brings together a number of important existing and new recommendations on ameliorating the negative impacts of large dams, it pays inadequate attention to the impacts in the major area (food production and security) for which dams have been built. Consideration of data presented by the WCD would suggest a more positive impact, and a brief review of national and world trends in food production suggests that irrigation , of which large dams are an intrinsic and central component , has underlain if not dominated the vast improvement in food availability that occurred in the second half of the last century. With water in crisis in many countries, planners, policymakers and politicians will continue to face challenging decisions on the allocation of limited freshwater supplies, and demands to increase the level of water resources development. Some guidance from the WCD is helpful, and some is flawed. Most importantly, much is missing, and to be useful, guidance must reflect rational and balanced, expert and rigorous assessment of all the impacts of the available options. Copyright © 2001 John Wiley & Sons, Ltd. La Commission Globale des Barrages a maintenant publiée son rapport. Quelques apercus sur les méthodes et les conclusions de la commission ont été données dans la dernière edition de ce journal. Quant le rapport CGB a se rassemblé quelques recommendations nouveaux et actuels pour amèliorer les impacts négatifs des grands barrages, il n'y a pas d'attention suffisante donnés aux impacts sur les questions importantes (comme le production et la sécurité d'alimentation) pour qui les barrages ont étés construits. Penser aux donnés du CGB suggère un impact plus positif et un critique des tendances nationale et globale du production d'alimentation denote que l'irrigation (dont les grands barrages sont un composant central et intrinsèque) a soutienne si non dominée l'immense amélioration de la disponibililité d'alimentation dans la dernière partie du XXe siècle. Avec la crise actuèlle de l'eau en beaucoup de pays, les planificateurs, les dirigants de politique et les politiciens se continuent de faire face aux decisions difficile sur les questions d'allocation d'eau limitée et les demands pour une augmentation de développement des resources en eau. Quelques conseils du CGB sont util mais quelques uns sont en défaut. Les plus importantes problèmes sont que le rapport manque beaucoup de choses et que, pour être utile, les conseils doivent réfléchir les impactes de tous les choix dans une façon rationale et équilibrée avec une évaluation experte et rigoureuse. Copyright © 2001 John Wiley & Sons, Ltd. [source] Evolution of the Irrawaddy delta region since 1850THE GEOGRAPHICAL JOURNAL, Issue 2 2010PETER J HEDLEY We present a time series of coastline change for the Irrawaddy delta region of Myanmar using the earliest available navigation chart from 1850, and a set of topographic maps and satellite imagery dating from 1913 to 2006. Despite the large sediment load delivered annually to the gulf by the Irrawaddy and Salween Rivers, the coastline has been largely stable for 156 years, advancing at an average rate of no more than 0.34 km per century since 1925. The long-term average rate of increase in land area across the study area between 1925 and 2006 is 4.2 km2/year, but this masks a period of more rapid accumulation between 1925 and 1989 (8.7 km2/year), followed by a period of net erosion at a rate of 13 km2/year until 2006. Less than 9% of the sediment load delivered to the study region by the Irrawaddy, Salween and Sittoung Rivers has contributed to the observed progradation, with the remainder being exported into the Gulf of Martaban to depths below low tide level, or filling any accommodation space created due to subsidence or sea level rise. In contrast to many deltas worldwide, we suggest that the coastline encompassing the Irrawaddy delta and the Salween River is more or less in equilibrium, and that sediment deposition currently balances subsidence and sea level rise. Myanmar has fewer large dams relative to its Asian neighbours, and the Salween is currently undammed. This is forecast to change in the next 5,10 years with extensive damming projects on the mainstem of the Salween under consideration or construction, and the sediment retention will cause losses in sediment supply to the Gulf of Martaban, and retreat of the delta. This could impact the densely populated delta region and Yangon, and further exacerbate the impacts of extreme events such as Cyclone Nargis in 2008. [source] Conservation and management of migratory fauna: dams in tropical streams of Puerto RicoAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2006Effie A. Greathouse Abstract 1.Compared with most other tropical regions, Puerto Rico appears to have dammed its running waters decades earlier and to a greater degree. The island has more large dams per unit area than many countries in both tropical and temperate regions (e.g. three times that of the USA), and the peak rate of large dam construction occurred two or three decades before reported peak rates in Latin America, Asia and Africa. 2.Puerto Rico is a potential window into the future of freshwater migratory fauna in tropical regions, given the island's extent and magnitude of dam development and the available scientific information on ecology and management of the island's migratory fauna. 3.The paper reviews the ecology, management and conservation of migratory fauna in relation to dams in Puerto Rico. It includes a synthesis of recent and unpublished observations on upstream effects of large dams on migratory fauna and an analysis of patterns in free crest spillway discharge across Puerto Rican reservoirs. 4.Analyses suggest that large dams with rare spillway discharge cause near, not complete, extirpation of upstream populations of migratory fauna. They also suggest several management and conservation issues in need of further research and consideration, including research on the costs, benefits and effectiveness of simple fish and shrimp passage designs involving simulating spillway discharge. The appropriateness of establishing predatory fish in reservoirs of historically fishless drainages also needs to be considered. Copyright © 2006 John Wiley & Sons, Ltd. [source] Ecological impacts of dams, water diversions and river management on floodplain wetlands in AustraliaAUSTRAL ECOLOGY, Issue 2 2000R.T. KINGSFORD Abstract Australian floodplain wetlands are sites of high biodiversity that depend on flows from rivers. Darns, diversions and river management have reduced flooding to these wetlands, altering their ecology, and causing the death or poor health of aquatic biota. Four floodplain wetlands (Barmah-Millewa Forest and Moira Marshes, Chowilla floodplain, Macquarie Marshes, Gwydir wetlands) illustrate these effects with successional changes in aquatic vegetation, reduced vegetation health, declining numbers of water-birds and nesting, and declining native fish and invertebrate populations. These effects are likely to be widespread as Australia has at least 446 large dams (>10 m crest height) storing 8.8 × 107 ML (106 L) of water, much of which is diverted upstream of floodplain wetlands. More than 50% of floodplain wetlands on developed rivers may no longer flood. Of all of the river basins in Australia, the Murray-Darling Basin is most affected with dams which can store 103% of annual runoff and 87% of divertible water extracted (1983,84 data). Some floodplain wetlands are now permanent storages. This has changed their biota from one tolerant of a variable flooding regime, to one that withstands permanent flooding. Plans exist to build dams to divert water from many rivers, mainly for irrigation. These plans seldom adequately model subsequent ecological and hydrological impacts to floodplain wetlands. To avoid further loss of wetlands, an improved understanding of the interaction between river flows and floodplain ecology, and investigations into ecological impacts of management practices, is essential. [source] Ecological impacts of dams, water diversions and river management on floodplain wetlands in AustraliaAUSTRAL ECOLOGY, Issue 2 2000R.T. Kingsford Abstract Australian floodplain wetlands are sites of high biodiversity that depend on flows from rivers. Dams, diversions and river management have reduced flooding to these wetlands, altering their ecology, and causing the death or poor health of aquatic biota. Four floodplain wetlands (Barmah-Millewa Forest and Moira Marshes, Chowilla floodplain, Macquarie Marshes, Gwydir wetlands) illustrate these effects with successional changes in aquatic vegetation, reduced vegetation health, declining numbers of water-birds and nesting, and declining native fish and invertebrate populations. These effects are likely to be widespread as Australia has at least 446 large dams (>10 m crest height) storing 8.8 × 107 ML (106 L) of water, much of which is diverted upstream of floodplain wetlands. More than 50% of floodplain wetlands on developed rivers may no longer flood. Of all of the river basins in Australia, the Murray-Darling Basin is most affected with dams which can store 103% of annual runoff and 87% of divertible water extracted (1983,84 data). Some floodplain wetlands are now permanent storages. This has changed their biota from one tolerant of a variable flooding regime, to one that withstands permanent flooding. Plans exist to build dams to divert water from many rivers, mainly for irrigation. These plans seldom adequately model subsequent ecological and hydrological impacts to floodplain wetlands. To avoid further loss of wetlands, an improved understanding of the interaction between river flows and floodplain ecology, and investigations into ecological impacts of management practices, is essential. [source] | |||||||||||||