摘要:

ABSTRACTAll electricity produced in Norway originates from hydroelectric power plants, some of which utilize glacier melt-water. In a special case, a subglacial water intake was constructed under Bondhusbreen, an outlet glacier from the Folgefonni ice-cap in southwestern Norway.To remove bed load material from the meltwater a large sedimentation chamber was constructed in the bedrock under the glacier. A program of taking bottom samples from a proglacial lake was carried out to obtain data to help engineers to design the correct dimensions for the chamber.Six vertical cores were taken from a flat bottom area of the glacier lake Bondhusvatn; five of them contained clearly laminated sand, silt and clayey material. Both annualvarvesand“pseudovarves”were identified. The thickest annual layers, which have been deposited since the end of the 17th century, were used to calculate the maximum annual bed load, for engineering purposes. A calculation of extreme sediment inputs in the past indicates that a maximum annual suspended load of 9100 m3occurs about twice per century. Therefore, the volume of the sedimentation chamber had to be designed to accommodate 10000 m3to prevent bed-load material from entering the diversion tunnel system.The paper describes the cores, the correlation of varve diagrams constructed from laboratory studies of the cores, and the dating of the cores, partly through available meteorological and hydrological data. The existence of“pseudo-varves”was probably related to seasonal variations in discharge; the dominant annual layers (varves) were related to high total annual discharge or other“extreme”hydrometeorological events. Finally, a smooth curve showing annual varve thickness was compared to similar curves for meteorologic elements.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880201

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTRecent overbank deposition of fine grained sediments along Swedish rivers is a rare process. Favourable conditions for overbank deposition exist, however, near the base level of low gradient rivers on the central Swedish plains. Lack of sedimentation data has inspired us to make this study which aims to estimate the present sedimentation rate and to test a field method to observe the spatial variation in deposition, by using simple sediment traps. The study area lies within the River Fyrisån drainage basin, previously investigated in several studies of fluvial geomorphology and sedimentology. The suspended sediment transport was calculated from actual discharge figures and from concentration figures obtained by water sampling and by using a“Surface Scatter Turbidimeter”. The total sedimentation in the deposition area was estimated in three ways, i.e. from actual figures on sediment transport, by a sedimentation formula and by using the results from the sediment traps. The surface deposition rates varied between 8 and 240 g/m2. The accuracy of the different methods is discussed in this paper.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880202

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTThe b-f-m diagram can be used to interpret the downstream hydraulic geometry of rivers. Six lines representing thresholds of adjustment to downstream changes in discharge and sediment load delineate twelve sets of responses. Rivers that plot within the same area of the diagram have similar directions of adjustment to increasing discharge, although the exact rates may vary considerably. The groupings of data indicate that neither general climatic setting nor the size of the drainage basin has any consistent influence on the downstream relations. Downstream hydraulic geometry does, however, seem to respond quickly and in a predictable manner to changes in discharge and sediment load. Rivers have different downstream geometries at different frequencies of flow, and therefore comparisons among rivers should be made at a common frequency of discharge. Some minimum-variance solutions for the most probable form of hydraulic adjustment can be represented as three-dimensional surfaces on the b-f-m diagram. These surfaces show the probability of different hydraulic geometries, their relative stability, and likely directions of change. The set of responses to downstream increases in discharge predicted to be the most probable is also the most commonly observed. This may indicate a tendency toward a common form of adjustment.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880203

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTDetailed study was made of river channel changes occurring on low terraces in the Warta valley, west-central Poland. From paleobotanical and radiocarbon dates available for paleochannel fills, it has been inferred that a braided channel pattern remained active up to and including the Oldest Dryas. River metamorphosis took place during the Bølling, resulting in a meandering channel with high geometric parameters. From the Holocene they gradually declined due to an increase in forest density. The dated meandering paleochannels represented the starting point of quantitative assessment of annual discharge variations. The estimation was based on the measurement of paleochannel geometry, on the study of bed load deposits and on the reconstruction of velocity by use of the Manning and Strickler empirical formulae.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880204

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTThe role of reservoirs and dams, silt-trap dams in particular, in reducing soil erosion in the gullied rolling loess areas of the Yellow River Valley, and sediment delivery into the Yellow River has been studied. The study is substantiated from the viewpoint of geology, germorphology and mode of soil erosion, and on the basis of observed data and results of in-situ investigations.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880205

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTRivers in the Huang-Huai-Hai plain, China, are deeply influenced by a variety of human activities including man-made effects on runoff, changes in the rate of sediment accumulation on the plain, alterations in river channel processes, migration of dissolved salts in soil, changes in groundwater and soil conditions near the rivers, and changes in the ecology of rivers and lakes. Changes in the Huang-Huai-Hai plain have been very great.Construction of major reservoirs in upstream reaches of rivers draining to the plain beginning after 1949 first reduced peak flows and, along with diminished flow caused by diversions for agriculture and industry and reservoir evaporation, subsequently made many rivers ephemeral in the lower reaches. Flow to the sea was reduced 52 percent and sediment more than 80 percent.“resulting in a reduction of the aggradation rate from 1.4 to 0.5 mm/yr. Sediment concentrations are as high as 61 kg/m3in rivers from the mountains. Channels initially deepened and narrowed, but with ephemeral flows aggradation renewed. Aeolian activity increased and channel form was determined by the interaction of wind and river flow. In sluices and behind barrages, standing water and wind action induced bank failure and deposition reaching at the most 2.6 m on the channel bed. Deposition at the coast increased with the decline in river flow. Salt concentrations also increased in the declining flow with deposition in depressions and behind levees and laterally adjacent to river beds 3 to 10 m higher than surrounding plains. A lowered water table, however, has also occurred and the area of salinization has been reduced in some regions by 50 percent. The area of lakes and quality of water have been reduced by reductions in inflow and pollutant discharge from industry; and agriculture Baiyangdian Lake was reduced from 280 km2to 160 km2and fish and shrimp production dropped 80 percent between 1965 and 1978.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880206

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTCoastal wetland loss in Louisiana, now considered to amount to more than 100 km2/year, is receiving ever increasing amounts of attention. This loss is the result of a variety of complex interactions among a number of physical, chemical, biological, and cultural processes. Important geologic phenomena include sea-level change, subsidence, compaction, and change in location of deltaic depocenters. Of the many catastrophic events that cause erosion, the hurricane with its high energy is the most important in Louisiana. Biological factors include rates of marsh growth (especially in relation to subsidence, compaction, and saltwater/freshwater proportion) and the degradation caused by marsh fauna.During the last few decades, the human factor in wetland loss has increased drastically. The placement of dams and levees across and along the tributaries and distributaries of the Mississippi River have reduced both the amount and texture of sediment reaching the coast. In addition, canal and highway construction in the wetlands has altered drainage patterns and fluid withdrawal is causing subsidence.To date, few of the processes responsible for land loss in south Louisiana have been quantified and the data sets that do exist are often in conflict with each other and reflect multiple interactions. However, the attention now being given wetland loss will hopefully provide more definitive answers in the near future.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880207

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTIt has been claimed, on the basis of relatively shortterm gage observations and the perceptions of riverbank dwellers, that height and duration of Amazon floods are increasing. The paper discusses these assertions and some of the processes that might lead to the predicated trends. Two such processes are: an increase in peak discharge and a decrease in channel cross-section. Both could be triggered or reinforced by human-induced changes in the environment. By altering the hydrologic relations of plant, soil and water, deforestation in the headwaters can enhance runoff. It can also increase the sediment load, which, if the carrying capacity of the river is exceeded, may be deposited in and aggrade the channel. That deforestation in the Amazon drainage, now affecting small affluents, will eventually bear upon the regime of major tributaries and of the main stem itself can hardly be disputed. However, given the vastness of the basin, and the proportionately small and concentrated areas impacted by settlement, reports that such effects are already perceptible thousands of kilometers from the cleared areas require careful scrutiny.A detailed statistical analysis, combining gage readings and adequate precipitation data, may, of course, reveal the existence, in one or more sections of the river, of long-term changes in flow that cannot be explained in terms of rainfall variability. Even then, one should not exclude the possibility that such trends might be elucidated without invoking human intervention. They might, indeed, be caused by stream adjustment to neotectonic influences.In relation to the testimony of riverine populations, major inundations are likely to polarize concerns and dim the memory of moderate floods.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880208

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTThe Western Carpathian Mtns of intermediate height are in the temperate zone. They belong to the Alpine mountain system; erodible flysch rocks are dominant.Pleistocene slope processes and the resulting aggradation of alluvia ended at the Pleistocene/Holocene transition, due to the quick succession of forest communities. As a consequence, the Holocene erosion took place in Carpathian valleys. The agricultural colonization which began in pre-historic times intensified in late medieval times, causing marked changes in the land-use pattern. Forest clearing favoured both erosion of the Pleistocene slope covers and deposition of this material in the Holocene valley floors. Since 3000 years B.P., natural levees have developed there.At the beginning of the 20th century, channel correction was undertaken on the major rivers. Both construction and shortening of the channels caused accelerated channel deepening. Rates of incision are still increasing.Large dams and reservoirs impounded in the last decades for hydro-electric purposes have tended to disturb drastically both the natural hydrologic regimen and sediment transport. Disturbances are especially distinct near the reservoirs, just upstream and downstream of the dams.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880209

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

ABSTRACTThis article deals with rill and gully erosion in a subhumid tropical region, the ravinated zone of the Jawa Block, Rewa District in Madhya Pradesh, India. The study area is situated in the intervening zone between the northern foreland of Peninsular India and the Gangetic Plain. The erosion processes have been initiated and accelerated by deforestation, overgrazing, and clearing of land for agricultural purposes. Gully morphology is partly controlled by lithological conditions. Field studies have revealed an alarming rate of gully extension, with an average loss of 2.35 million m3of agricultural soil per year. It is estimated that the affected area will increase by 50% in the next 50 years.

ISSN:0435-3676    

DOI:10.1080/04353676.1987.11880210

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor