Dynamiques hydrogéomorphologiques historiques et actuelles d'une rivière perturbée par les activités de la drave et analyse des impacts d'un démantèlement de barrage

In Quebec, the fluvial dynamics of the Escoumins River have been disturbed by the forestry industry for over a century. Most specifically, a dam was built near the mouth of the river in 1846 and dismantled in 2013. These disturbances had significant repercussions on the equilibrium of the river and Atlantic salmon habitat. This study therefore proposes to characterize the fluvial dynamics of the Escoumins River and to analyze the impacts of the dam dismantling from the perspective of restoring hydrogeomorphological processes and improving Atlantic salmon habitat. The results suggest that the trajectory of the river evolved differently depending on the fluvial style and the grain size composition of each of its homogeneous segments. However, log drive activities in river and dam removal appear to have been the most important controlling factors on the evolution of the stream trajectory. The dismantling notably allowed the restoration of hydrogeomorphological processes and the free movement of salmonids. A better procedure for dam removal and monitoring should be put in place in Canada to encourage this practice.     

The need for river management and stream restoration practices to integrate hydrogeomorphology

There is growing support amongst scientists worldwide about the need for a shift in river management approaches to include hydrogeomorphic processes. However, the degree to which these concepts are transferred to governmental agencies and practitioners varies widely. In Quebec, for example, many stream restoration projects are based on the (incorrect) assumption that river mobility and its inevitable consequences (bank erosion of meanders, presence of woody debris in the channel) are problematic for salmonids. This paper presents examples drawn from current guidelines on stream restoration for fish habitat in Quebec to demonstrate the need to improve the knowledge exchange among scientists and decision makers about the positive impact of river mobility and large wood dynamics on biodiversity. Our observations reveal that existing guidelines for stream restoration in Quebec need to be revised to better integrate hydrogeomorphic concepts and to no longer assume that maintaining rivers in a static state is beneficial for fish. Adopting the “freedom space for rivers” approach would likely result in improved habitat as it combines natural processes related to mobility, flooding, and riparian wetland connectivity to determine the minimal space around rivers where development should not be allowed, thus allowing river processes to be restored.     

History and Effects of Channelisation on the Latrobe River,Victoria

Channel changes on the lower Latrobe River since the late 1800s include a 25 per cent reduction in channel length due to artificial meander cutoffs, increases in mean channel width, increased channel instability and incision of up to 1.05 m. Hydraulic changes at the Rosedale gauge include increases in bankfull flow velocity and a 67 per cent increase in channel capacity, resulting in a threefold reduction of over-bank flow duration. The extensive channelisation works have reduced the frequency of minor flooding and the period offloodplain inundation, but these and other human impacts have severely degraded the stream environment.     

Water,Wind, Wood,and Trees: Interactions,Spatial Variations,Temporal Dynamics,and their Potential Role in River Rehabilitation

Recent Australian research has quantified the role of large wood (wood of any origin and length with a diameter greater than 0.1 m) in dissipating stream energy, forming pool habitats by local bed scour, protecting river banks from erosion, and damming rivers with long rafts causing avulsions. Large wood in Australian streams is sourced by a range of processes from the nearby riparian zone which has usually been degraded by post‐European settlement vegetation clearing. Large wood loadings within the bankfull channel are dependent not only on the type and quality of the riparian plant community but also on bankfull specific stream power, channel width, and the processes of large wood delivery to the stream. While bank erosion and floodplain stripping by catastrophic floods are obvious and important delivery mechanisms, treefall and trunk and branch breakage by strong winds during tropical cyclones and severe storms are also significant in the tropics. Furthermore, wood decay and downstream transport produce temporally dynamic large wood distributions. The longevity of natural large wood structures in rivers, such as rafts, debris dams, and log steps, requires determination. River rehabilitation programs need to not only include the reintroduction of large wood, but also carefully plan the spatial distribution of that wood, the most appropriate type and range of large wood structures, and, most importantly, the revegetation of the riparian zone to ensure a natural long‐term source of large wood. Exotic species management is an essential part of river rehabilitation.     

River metamorphosis and environmental change in the Macdonald Valley,New South Wales,since 1949

A significant metamorphosis of channel form occurred on the lower Macdonald River between 1949 and 1955; width and width-depth ratio increased and depth, sinuosity and weighted mean per cent silt-clay in the channel perimeter decreased. The channel has remained unstable since 1955, exhibiting frequent variations in bed elevation and a recent period of minor channel contraction followed by slight enlargement. Since 1946 there has been an increase in summer and annual rainfall and an abrupt, upward shift of the annual series flood frequency curve. As a result an increased proportion of the total sediment load of the river is now being transported as bed-material load. The change in sediment load is a result of greater stream competence and the consequent reworking of sandy sediment temporarily stored within the channel as benches. The observed channel changes are a quasi-adjustment to the increased flood and bed-material load discharges.     

DEVELOPMENT OF THE CASPIAN SHORELINE UNDER THE PRESENT INCREASE IN ITS LEVEL

The authors, questioning the implications for the Caspian of a conventional model of shoreline dynamics on a flat, sandy coast upon a rise in sea level, present the findings of field observations made along the Dagestan shore during the period (post-1977) of the recent rise of the Caspian Sea level. They argue that changes in coastal morphology have varied largely according to the steepness of the offshore slope and, in general, sharply accelerated erosion was observed only on more steeply sloping sections of coast and in areas previously protected by rock benches (translated by Jay K. Mitchell; PlanEcon, Inc.; Washington, DC 20005).     

THE CAUSES OF WATERLEVEL CHANGES OF THE ARAL SEA IN THE HOLOCENE

A specialist in loess geomorphology and arid-zone hydrology distinguishes three categories of factors accounting for waterlevel changes in the Aral Sea. She judges the most significant to be changes in inflow resulting from changes in the course of the Amudarya, the more important of the two tributary streams. The Amudarya at various times emptied into the Sarykamysh depression, southwest of the Aral Sea, giving rise to a flow of water through the now dry Uzboy channel to the Caspian Sea. Climatic change, involving alternations of wet and dry cycles, is said to have accounted for only minor water level fluctuations, of the order of 4 to 6 m, against the background of the major fluctuations produced by the Amudarya course migrations. Human activity, notably irrigation, is regarded as having become significant only in modern times as a result of an expansion of irrigation works. The present abrupt decline in the Aral waterlevel (6 m from 1960 to 1977, including 2 m in the last three years) is attributed to the combination of a dry climatic cycle and greatly increased use of water for irrigation.     

THE MORPHOMETRY OF THE CASPIAN SEA BASED ON CONTEMPORARY DATA

Differences in available data on the area of the Caspian Sea are analyzed, and an effort is made to explain them. The differences are particularly pronounced in the shallower northern portion of the sea, where the drop of the sea level over the years has produced more significant changes in shoreline configuration. Greater use of space imagery is urged in determining changes in shoreline configuration, and the setting of “geographical standards” is proposed to avoid continuing confusion in published data. The technical problem of calculating the physical water area, including surface roughness produced by wave motion, is discussed.     

近代长江流域行轮内港时空变迁研究(1898—1929年)——基于《<内河行轮章程>项下华洋轮船行驶 内港名录》的复原

1898年清廷颁布《内港行船章程》后,长江内河轮运骤兴,开放轮船行驶的内港日渐增多,截至1929年全流域有超过418处内港开放行轮,内河航运格局为之一变。长江流域开放行轮的内港在空间上集中于下游地区,中游也有较多分布,上游地区则十分稀少。行轮内港的开放在时间上则呈现出下游到上游、干流到支流两种趋势。近代行轮内港的时空变迁趋势反映了轮运这一新式交通在长江流域的发展情况。     

泾、浜发展与吴淞江流域的圩田水利(9-15世纪)

自宋代的塘浦系统开始瓦解以来,吴淞江流域的泾浜体系开始发展。泾浜水系和以后溇的出现,基本上人为形成的。在不断的历史发展中,泾浜体系形成具有干枝结构的网状水系,这种结构非常稳定地存在了近500年。这种结构下的圩田水利模式一般是小圩模式。在冈身感潮地区,泾浜体系比较密集,且末端水系有弯曲化现象;在低地地区,为了排水的方便,河道的干枝体系较为顺直。在这种体系下,治水必须与治田相结合。到后期,随着圩田治理的深化,进一步出现了称为溇的末端水系。     

Keeping Pace With Rising Sea: The First 6 Years of the Lower Suwannee Archaeological Survey,Gulf Coastal Florida

Low-gradient coastlines are susceptible to inundation by rising water, but they also promote marsh aggradation that has the potential to keep pace with sea-level rise. Synergies among hydrodynamics, coastal geomorphology, and marsh ecology preclude a simple linear relationship between higher water and shoreline transgression. As an archive of human use of low-gradient coastlines, archaeological data introduce additional mitigating factors, such as landscape alteration, resource extraction, and the cultural value of place. The Lower Suwannee Archaeological Survey (LSAS) is an ongoing effort to document the history of coastal dwelling since the mid-Holocene, when the rate and magnitude of sea-level rise diminished and the northern Gulf coast of Florida transitioned into an aggradational regime. Results of the first 6 years of the LSAS suggest that multicentury periods of relative stability were punctuated by site abandonment and relocation. Subsistence economies involving the exploitation of oyster and fish, however, were largely unaffected as communities redistributed themselves with changes in shoreline position and estuarine ecology. After AD 200, civic-ceremonial centers were established at several locations along the northern Gulf coast, fixing in place not only the infrastructure of daily living (villages), but also that of religious practice, notably cemeteries and ceremonial mounds. Intensified use of coastal resources at this time can be traced to a ritual economy involving large gatherings of people, terraforming, feasting, and the circulation of socially valued goods. To the extent that religious practices buffered the risks of coastal living, large civic-ceremonial centers, like aggrading marshes, afforded opportunities to “outpace” sea-level rise. On the other hand, centers introduced a permanence to coastal land-use that proved unsustainable in the long term.     

A Comparison of Holocene and Historical Channel Change along the Macdonald River,Australia

Changes in channel morphology that occurred along the Macdonald River between 1949 and 1955 are often cited as an example of catastrophic channel change. However, the question of whether these changes represented one component of a cyclical evolutionary pattern, or a systematic and persistent shift to a new morphologic state remains to be clearly defined, as does the significance of these dramatic channel changes when viewed against the river's longer‐term Holocene history. In this paper, new measurements of the Macdonald River's channel morphology are used to resolve the river's evolution in the ～50 years since these major channel‐altering floods. By 2002, the Macdonald River's bed had narrowed considerably from its 1955 post‐flood maximum due to the construction of a new floodplain surface within the widened channel. In some locations, the 2002 bed width is comparable to that of the pre‐1949 channel. This aspect of the river's evolution follows models of cyclical channel evolution proposed for the region. However, in light of recent research into the river's longer term Holocene evolution, it is clear that other channel changes that occurred in response to the 1949–1955 floods, particularly the 2 metres of river bed aggradation and 7 kilometres down‐valley shift in the thalweg's intersection with mean sea level, are less cyclic in nature. The capacity of coastal rivers to prograde into estuaries, which in turn induces river bed aggradation, can be seen in this case to counteract the incisional tendencies associated with post‐flood channel contraction, such that persistent river bed aggradation occurs.     

Changes in stream channel morphology at tributary junctions,Lower Hunter Valley,New South Wales

Many empirically derived models of downstream changes in channel form are based on the concept of hydraulic geometry, whereby changes in channel morphological variables are related by a continuous power function to increasing discharge or its surrogate. However, changes in discharge throughout a drainage basin are normally concentrated at the junctions of stream channels. At junctions, the relationship between discharge and channel morphology is discontinuous. Some Lower Hunter Valley stream channels were surveyed upstream and downstream of tributary junctions. While significant regional downstream relationships were established, consistent trends at tributary junctions were not apparent from the data. It is possible that considerable scatter evident in ratios of change on either side of each junction was due to local within-site variability. In addition, the relative timing of discharge inputs and the nature of introduced sediment loads could be important in determining the magnitude and direction of channel change at tributary junctions. Interrelated changes in cross-sectional, profile and planform variables may be expected below junctions. The resultant channel morphology, in terms of these variables, might not be wholly determinate.     

CHANGES IN THE STRUCTURE OF EVAPORATION IN THE ARAL SEA BASIN

An analysis of evaporation changes in the Central Asian plain in connection with the drop of the Aral Sea level beginning in 1961 shows that there has been a reduction in evaporation from stream valleys and deltas and an increase in evaporation from irrigated land and newly formed evaporating surfaces. These new entities are primarily the Arnasay depression (west of the Golodnaya Steppe irrigation district) and the Sarykamysh depression (west of the lower reaches of the Amudarya), which have become filled with spent irrigation water draining from the irrigated land. Another new source of evaporation associated with human activity are the lakes and wetlands formed along the Kara Kum Canal as a result of the filtration of canal water. It turns out, furthermore, that irrigation on sloping piedomon plains, such as those watered by the Kara Kum Canal, requires more water than in old irrigated alluvial plains because of the additional water needed to flush salt out of the soil and to fill subsoil cavities and raise the watertable.     

Morphological Impacts and Implications of a Trial Release on the Wingecarribee River,New South Wales

A trial, monitored release on the Wingecarribee River over 27 days had a peak discharge below the Wingecarribee Dam of 1090 ML/d, which had a flow duration of 0.95 per cent. Morphological impacts on 29 km of channel below the dam included bank erosion, concentrated neck overflow, bed degradation and channel widening at recent cutoffs, sedimentation in weir pools and overbank flow, particularly at discharges greater than 800 ML/d. Prolonged operational releases at bankfull discharge (400–800 ML/d) will have the greatest morphologic impacts and should be avoided. Pulses which dissipate stream power over a broad, well-vegetated floodplain should be incorporated in the operational release policy, provided such pulses are phased to facilitate channel and vegetation recovery.     

The rock art of the Côa valley,Portugal: Significance,conservation and management

Abstract

The Côa river valley is the largest open-air Palaeolithic art site currently known. Some 150 decorated panels have already been found, spread along 17km. The whole complex would have been submerged under 100m of water if construction of the large Foz Côa dam, begun in 1992, had been allowed to continue. The dam project was halted in 1995 and a 200km² archaeological park is being established in this area, which is now legally protected at the highest level as a National Monument. Public access to selected sites is organized through four-wheel drive. tours of groups of eight people accompanied by guides appropriately trained in archaeology and rock art studies. Visitor Centres have been set up in restored traditional houses located in the villages around the periphery of the park. A Museum of Rock Art and Archaeology and associated research facilities is to be established at the site of the now abandoned dam.     

明初大运河南旺分水枢纽水工技术考

明朝初年,国脉皆仰东南,为解决南方粮财物的北运问题,宋礼和白英受命组织修建了大运河山东段南旺分水枢纽。该枢纽主要包括引汶济运、导泉补源、设立水柜和置闸节流四个组成部分。其中,引汶济运是工程之重点,包括戴村坝、小汶河、南旺分水以及配套工程等四个子系统。这些水利设施组成一个和谐的系统工程,保证了该段运河的水量稳定充足,从而实现了大运河500余年的正常通行。南旺分水枢纽代表了我国古代运河水工的最高科学技术成就,堪称世界水利史上的一大经典范例。     

Do We Really Understand Our Rivers? or Rivers in the Pooh - Semper in Excreta!

This address is concerned with the lack of detailed understanding we have of rivers. It is argued that to manage river systems for environ- mental and ecological sustainability, there must be understanding of riverine biophysical processes. These are explored through a consideration of: (1) channel airspace and water; (2) the perimeter conditions of the channel as the boundary between erosional channel and depositional floodplain, both of which occupy the valley-floor trough; (3) ecological components of channels and (4) the human components where human interactions with catchment environments have such impacts on the biophysical systems. Finally, the implications of these four components for understanding the systems for more sustainable management are discussed.     

Observations Of Water Hardness From Southwest Devon Island, Northwest Territories

Over the thaw period of 1970, the hardness in “Jason's Creek” increased systematically. Waters from other sources in the area, sampled in 1969 and 1970, show increases in hardness with distance of travel downslope, from large flows to small flows, and from flowing water to standing water. The highest total hardness values are from vegetated pools of standing water (as also reported by Smith (1969) in Somerset Island). The hardness of water which has had no contact with regolith or bedrock can be sharply differentiated from that of water which has been in such contact. This observation, together with the increase in hardness with distance of travel, may be consequent upon a slow attainment of chemical equilibrium in these arctic waters. It may also be possible to draw a distinction between the solutional work done by snowmeit water and that done by rainwater. The latter has a lower initial pH and, for comparable volumes of discharge, generates higher values of hardness. These preliminary conclusions are to be tested in future stages of this project, which in 1971 and 1972 will be concerned with the hydrology of a larger stream, the river Mecham, near Resolute on Cornwallis Island. Monitoring of the solute content of waters throughout the Mecham basin is an important part of the proposed research.     

A River Runs Through It: Morphological and Landowner Sensitivities Along the Upper Missouri River, Montana, USA

Landowners along the Missouri River in Montana believe that the operation of Fort Peck Dam has initiated bank erosion, thus threatening agricultural development within the region. Their concerns have been heightened by proposals to increase discharge in order to enhance fisheries and wildlife interests. Geomorphological evaluation indicates that bed degradation and bank erosion have declined since construction of the dam, and the channel is now approaching dynamic equilibrium; public sensitivity to the proposed change is greater than the morphological sensitivity of the river. Sustainable management of the Missouri is now based on strategies that place more emphasis on partnership with local citizens.