Water Level In Channel Research Articles

댐이 하류하천에 미치는 영향권 산정에 관한 연구

본 연구에서는 댐이 하류하천에 미치는 영향권을 산정하기 위하여 수리 수문적, 지형적, 환경 생태적, 사회적 영향의 4개 지표와 38개 항목을 선정하고, 계층분석법을 적용하여 댐의 영향권 산정 지표와 항목의 중요도를 평가하였다. 댐 영향권 산정 지표의 평가결과는 수리 수문적 영향권이 1순위, 환경 생태적 영향권이 2순위, 지형적 영향권 및 사회적 영향권이 각각 3순위와 4순위 이었으며, 항목의 평가결과는 댐설계방류량이 1순위, 하천의 기본 및 계획홍수량이 2순위, 계획홍수량비가 3순위, 유역면적비가 4순위, 하류댐 배수위가 5순위로 평가되었다. 대청댐의 영향권을 산정한 결과, 댐설계방류량 지표는 47.21 km, 하천계획홍수량 지표는 45.71 km, 유역면적비 지표는 13.94 km로 산정되었다. In this study, 4 indices of hydraulic & hydrological, geomorphological, eco & environmental, social effect and 38 items are selected to calculate impact range of downstream of dam. The Analytic Hierarchy Process(AHP) was applied to determine the priority of impact range calculation indices and items. As results of indices valuation, hydraulic & hydrological effect is the first priority, the second is eco & environmental, next are geomorphological and social effect. As results of items valuation, the design flood of dam is the first priority, the second is the natural flood & design flood of channel, next are the design flood rate of channel, drainage area and back water level caused by downstream of dam. In the case of Daechung dam, impact ranges were estimated 47.21 km in terms of the design flood of dam, 45.71 km of the design flood rate of channel, 13.94 km of the drainage area.

Detection of Oscillatory Control Loops in Irrigation Channels

In this paper the algorithm for detection of oscillatory control loops developed in Hägglund (1995) is applied to irrigation channels. The water levels in irrigation channels are controlled using mechanical gates. The controller configuration is a decentralized distant downstream scheme where a gate controls the water level upstream of the next downstream gate. The controller is a PI controller augmented with a low pass filter together with a feedforward term from the downstream gate. The algorithm is applied to real data from six consecutive reaches of an irrigation channel, and it detected the control loops that gave oscillatory response. Furthermore, due to the decentralized configuration, one is also able to localize the cause of the oscillation. Given that there can be many control loops in a channel network, the ability to localize the cause of an oscillation speeds up the trouble shooting process. However, care must be taken in choosing the thresholds in the algorithm in order to avoid frequent false alarm.

Behaviour and growth of juvenile brown trout exposed to fluctuating flow

Abstract – Parr of brown trout (Salmo truttaL.) were exposed to constant or fluctuating water level and flow in artificial outdoor stream channels during 21 days in three consecutive runs, and their individual behaviour and social interactions were monitored. Despite the large variation in flow, no clear differences in growth, which was generally poor, and behaviour were found between treatments. The signs of a social structure in the stream channels were very subtle and there were no clear relation between growth rate and aggressive/dominant behaviour in any of the treatments in accordance with findings in studies of growth and dominance in the wild. Thus, in regulated rivers, daily fluctuations in flow and water level (hydropeaking) are not likely to alter the behaviour of juvenile brown trout or affect their energy turnover negatively. Several studies now indicate that if stranding can be avoided, hydropeaking has relatively small direct effects on stream salmonids. Therefore, future research should focus on cascading ecological effects that may influence the productivity of the ecosystems in regulated rivers.

Hydrodynamics of floodplain wetlands in a chalk catchment: The River Lambourn, UK

Variations in floodplain channel water levels and valley floor groundwater levels (measured in piezometers and boreholes) are examined at selected points along the course of the River Lambourn, a chalk river in southern England. A local alluvial gravel aquifer in the valley bottom is associated with numerous small wetlands that extend over much of the river's perennial profile. Variations in hydraulic gradient between local borehole levels and/or floodplain channel water levels are described for three sites in the seasonal section of the channel at Bockhampton, East Garston and West Shefford. The results indicate that observed groundwater levels are closely associated with flows from discrete springs at the margins of the channel and floodplain. However, as the floodplain widens and the alluvial gravel aquifer increases in size, the gravel aquifer accounts for a substantial down-valley component of groundwater flow with a diffuse vertical water flux. In the lower catchment, the exchange of flows between the gravel aquifer and the river enables some attenuation of floodplain water-table variability, providing a stable hydrological regime for valley-bottom wetlands. Catchment controls upon the local, valley-bottom, wetland regime are demonstrated with the application of a simple groundwater model developed using MODFLOW. The model is used to simulate groundwater discharge to the river in the upper and lower catchment, in addition to the water level regime at selected points in the valley bottom in the lower catchment. The results demonstrate the importance of taking catchment-scale water flow into account when managing isolated wetlands in a permeable catchment.

Numerical simulation of overbank processes in topographically complex floodplain environments

AbstractThis article presents results from an investigation of the hydraulic characteristics of overbank flows on topographically‐complex natural river floodplains. A two‐dimensional hydraulic model that solves the depth‐averaged shallow water form of the Navier–Stokes equations is used to simulate an overbank flow event within a multiple channel reach of the River Culm, Devon, UK. Parameterization of channel and floodplain roughness by the model is evaluated using monitored records of main channel water level and point measurements of floodplain flow depth and unit discharge. Modelled inundation extents and sequences are assessed using maps of actual inundation patterns obtained using a Global Positioning System, observational evidence and ground photographs. Simulation results suggest a two‐phase model of flooding at the site, which seems likely to be representative of natural floodplains in general. Comparison of these results with previous research demonstrates the complexity of overbank flows on natural river floodplains and highlights the limitations of laboratory flumes as an analogue for these environments. Despite this complexity, frequency distributions of simulated depth, velocity and unit discharge data closely follow a simple gamma distribution model, and are described by a shape parameter (α) that exhibits clear systematic trends with changing discharge and floodplain roughness. Such statistical approaches have the potential to provide the basis for computationally efficient flood routing and overbank sedimentation models. Copyright © 2002 John Wiley & Sons, Ltd.

Late Devensian ice sheet characteristics: a palaeohydraulic approach

Glacial meltwater channels are incised into bedrock and diamicton along much of the length of the Mid-Cheshire Ridge. Detailed mapping of one such system near the town of Helsby reveals a dendritic channel network developed in the opposite direction to the regional ice flow during the last (Late Devensian) glaciation. The channels formed subglacially, under atmospheric and not hydrostatic pressure, presumably as the ice sheet downwasted during deglaciation. Morphological and palaeohydraulic evidence suggests that not all of the network was necessarily active contemporaneously. Former water levels in the channels can be estimated due to the presence of bar surfaces, giving a calculated palaeodischarge of at least 111 m3 s−1. The ablation rates required to account for this large discharge are an order of magnitude greater than those obtained from theoretical calculations and those observed in modern glacial environments. This implies that some form of high-magnitude discharge, such as a seasonal flood event, must have taken place in this area during deglaciation. This picture of the Late Devensian ice sheet suggests that during recession the ice sheet was static, crevassed and relatively thin (<50 m). This study also shows that there is no simple relationship between meltwater channel direction and ice dynamics, and that care is required when using the former to make inferences about the latter. Copyright © 1998 John Wiley & Sons, Ltd.

A numerical study of bank storage and its contribution to streamflow

Floodplains mitigate against extreme annual hydrologic phenomena by storing substantial volumes of water which would otherwise increase flood volumes. Later floodplains gradually release this water which serves to maintain baseflows. This phenomenon, called bank storage, has important physical and ecological ramifications which in addition to reducing flood peaks, include sustaining riparian vegetation and improving water quality. We developed a model of bank storage based upon the earlier work of Neuman and Witherspoon (Wat. Resour. Res., 6 (1990) 889, 1376; 7 (1971) 611). This model (WaTab2D) treats the flow of water through floodplain soils for a general two-dimensional case: non-symmetrical valleys, non-symmetrical channel banks, non-uniform hydraulic geometry and non-zero boundary fluxes. The total volume that can potentially be released from bank storage is nearly proportional to the width of the floodplain, the height of the bank, and the specific yield; the duration over which water is released from bank storage increases with increasing floodplain width and decreases with hydraulic conductivity. Drainage of water from the floodplain with a drop in channel water level occurs over a period of days in gravel, weeks to a few years in sand, years in silt, and decades in clay. The rate of drainage decreases in an exponential-like manner.

Factors affecting distribution of instability of river banks in the Niger delta

The Niger delta is intensely dissected by a network of rivers which erode and continuously reshape their banks resulting in net riverbank recessions. The rates of bank recession depend on season, soil type, bank height and stratigraphy, flow velocity and relative location along the river system. Bank failures occur by several mechanisms. These include; rotational, translational, overhang/toppling and flow mechanisms. Bank failure episodes are concentrated at the early stages of lowering of channel water level due to the sensitivity of banks to removal of passive resistance. High ground-water level accentuates seepage erosion which reduces bank stability. To realistically predict the behaviour of river banks, the method of evaluation must recognise the dynamic nature of the controlling factors.

Control of channel bank erosion using permeable groins

An experimental erosion control scheme in the Niger Delta was designed as a permeable groin using timber piles laced with strong cane nets. At the onset of the rains, when external channel water level was only 10 percent of its seasonal peak, a failure of the peripherial groin was recorded, which apparently was due to local sliding in the bank. At peak flood, a timber pile probably buried to a shallow depth failed, making the system of groins ineffective. The failure of the single timber pile resulted in extensive scouring and bed degradation, leading ultimately to the failure of the protective structure. Analyses carried out confirm that depth of embedment of the pile system is the single most important factor ensuring the stability of the groin structure.

Influence of a Beaufort Sea Storm Surge on Channel Levels in the Mackenzie Delta

A storm surge in the Canadian Beaufort Sea during September 1985 resulted in a maximum water level of 1.73 m asl and a maximum surge component of 1.38 m at Tuktoyaktuk. This surge resulted in rises in channel water levels of 1.05 m in the outer delta, 0.66 m in the middle delta and 0.16 m in the upper delta, with the peak water levels at these stations lagging 4, 17, and 21 hours respectively behind the peak water level in the Beaufort Sea. This surge clearly illustrates a number of points. First, throughout the Mackenzie Delta increased water levels resulting from surges must be taken into account when calculating channel discharge from a stage-discharge relationship. Second, storm surges play an important role in the flooding of delta lakes. However, further work is required to illustrate the relative importance of flooding by the Mackenzie River versus storm surge related flooding. Third, the surge of September 1985 illustrates the potential effect of rising sea level. Although this surge cannot be used as a direct analogue for future sea level rise because the dynamics of the system are non-linear, it clearly shows that a rise in sea level would have a major impact on the water level regime of delta channels and lakes. Further work should utilize a numerical simulation model to illustrate the effect of rising sea level on water levels in the Mackenzie Delta.Key words: Mackenzie Delta, storm surge, channel water levels, climate change

Lake evolution during the past 30,000 years in China, and its implications for environmental change

Throughout China over the last 30,000 years high lake levels were reached during 30,000–24,000, 22,500-20,000, and 9500-3500 yr B.P. Lake recovery after the last glacial maximum (LGM) apparently was much slower, and involved stronger regional differences, than was lake regression during the onset of the last glaciation. According to the character of lake development during the last 18,000 years, three regions and six subregions have been distinguished. In the Tibetan Plateau and alpine regions of western China the plentiful supply of meltwater may have caused lakes to recover and reach their highest levels fust after the LGM. Lake hydrology in central and northern China was directly controlled by rainfall and evaporation, and most lakes reached their highest levels between 9500 and 3500 yr B.P. In the lowlands of eastern China lake recovery was closely tied with channel aggradation and water level rise of rivers, which are associated with Holocene sea level rise and human agricultural activities. Most lakes recovered and were most extensive in the middle and late Holocene.

DEVELOPMENT AND TESTING OF A WATER MANAGEMENT MODEL (WATRCOM): FIELD TESTING

ABSTRACT BSTRACT Water table observations from the 1000 ha watershed of Mitchell Creek near Tarboro, NC, were used to field test the water management model, WATRCOM. Soil properties and channel boundary conditions from three sections of the watershed along with weather data from years 1983 and 1984 were used to simulate the hydrology of the area with and without channel water level control. Six transects containing 27 water table observation wells were selected for testing. All simulations were based on measured field parameters and no calibration simulations were made to optimize parameters to fit observed data. A total of 14,000 daily water table observations were compared with simulated data. The root mean square error in simulated water tables at each well ranged from 0.05 to 0.24 m. When the data were pooled by section, the root mean square error ranged from 0.10 to 0.17 m.

Development And Testing Of A Water Management Model (Watrcom): Development

ABSTRACT Drainage is required in many agricultural watersheds in the southeastern United States for flood prevention and to sustain agricultural production. These drainage improvements often increase the severity of summer droughts by lowering water tables. A computer simulation model, WATRCOM, has been developed to assist in evaluating drainage improvements and the feasibility of using channel water level control. A finite element solution of the Boussinesq equation coupled with water balances in the unsaturated soil and on the surface is used to simulate water movement in three dimensions. Varying soil types and boundary conditions in land areas with irregular drainage channel networks can be considered. Model results are compared to published solutions for drainage to parallel drains. Solutions are also presented for flow in regions near intersecting drains and compared to solutions in regions with parallel drains.

The Flooding Hydrology of Mackenzie Delta Lakes near Inuvik, N.W.T., Canada

The hydrologic regime of lakes in the Mackenzie Delta is controlled primarily by lake sill elevations and water levels in the Mackenzie River distributary channels. The resulting variations in lake regime have important effects on the water, sediment, and nutrient balance of delta lakes, and therefore on the biologic regime of each lake. Analysis of 12-25 years of Mackenzie River East Channel water levels allowed the documentation of the relationship between flooding regime and sill elevation for lakes in the study area near Inuvik, N.W.T. These data showed that in this portion of the delta, the timing of the spring rise in water levels is very consistent, with peak levels, for example, occurring on 3 June with a standard deviation of only 4 days. The magnitude of the spring flood varies greatly from year to year, and as a result only 67% of lakes in the study area flood annually in the spring, while the remaining lakes have a flood frequency of greater than 1 year and less than 4 years. Since the mean summer flood peak of 2.777 m asl is considerably lower than the mean spring peak of 5.636 m asl, summer lake flooding is not as extensive, with only 20% of lakes receiving floodwater annually during the summer. By late summer, water levels drop to 1.5 m asl annually, cutting off approximately 88% of lakes from the Mackenzie River. These data on the return period of lake flooding allowed the classification system described by Mackay (1963) to be quantified. The no-, low- and high-closure lakes were found to represent 12, 55, and 33% respectively of all lakes in the study area. Variations in the hydrologic regime of the Mackenzie River could occur in the future due to hydro-electric development, climate change, or rising sea level. Even small changes in Mackenzie River levels could result in a significant modification to the hydrologic regime of delta lakes. The effects on the viability of these lakes, or their chemical and nutrient balances, are not well known.Key words: Mackenzie River, Mackenzie Delta, hydrology, lakes

Application of a Three-Dimensional Water Management Model

ABSTRACT COMPUTER simulations were conducted to evaluate the effects of channel water level control on the conservation and management of shallow groundwater resources in agricultural drainage districts. Drainable water stored in the profile, crop evapotranspiration, and relative corn yields were used to evaluate the conservation of stream flow and rainfall. The effects of management of shallow groundwater were determined and evaluated for the availability of channel water for withdrawal. The simulations were performed for a 0.734 km^ area adjacent to a section of Mitchell Creek near Tarboro, NC for 2 yr, 1983 and 1984. Channel water level control increased the simulated drainable water stored in the profile by 85 mm in 1983 and by 84 mm in 1984. Simulated relative corn yields were increased in land areas upstream from the water control structure. Yield increases were greatest for land within 100 m of the controlled channel. Channel control provided sufficient shallow drainable groundwater for 17 days of drought compared to only 4 days without control for the periods simulated.

STABILITY OF CLAY CHANNEL LININGS.

The paper considers the stability of a clay lining to control water leakage from a channel formed in essentially granular permeable material. Expressions for factors of safety are derived using effective stress strength parameters for the clay and assumed pore pressure conditions during normal channel operation, and during channel filling and drawdown. These expressions show that a particularly critical zone occurs at the water level in the channel, and that lining stability increases with decreasing thickness and increasing depth below channel water level. Measures for increasing lining stability are suggested. /Author/TRRL/

Quelques applications de modèles mathématiques à l'étude des écoulements non permanents dans un réseau ramifié de rivières ou de canaux

Mathematical models are coming into increasing use as a means of investigating unsteady river and channel flow. Their potential scope is briefly described. The Saint-Venant equations for gradually varying unsteady flow constitue a hyperbolic quasi-linear system. They can be integrated by two basic numerical methods : explicit methods requiring a stability condition, and implicit methods which may be unconditionally stable. The choice of which method to use is very often given by the type of problem, for whereas the increment along the abscissa depends on river or channel bed geometry and water level definition accuracy, the time increment, on the other hand, must account for significant variations. In the case of a flood (a 'slow' phenomenon) the implicit method is the obvious one as it can cope with a comparatively large time increment. Very rapidly developing phenomena, on the other hand, require a short time increment, which satisfies the stability condition of explicit methods. Each problem is represented by a hydraulic scheme allowing for the various ramifications and featuring all the weirs, flow inputs, cross-sectional changes, diversions and other special points in the system. One or two conditions (hydrograph or level chart) will be given upstream from each branch, and a stage/discharge relationship or a level record downstream from the model, also an operating relationship for each singular point. The initial conditions also require defining. They can be calculated for steady flow, but if the phenomenon is already developing at the point at which the calculation starts, they have to be assumed ; they are usually of little importance, however, as their effects are no longer felt after a certain time. Reference is made to examples of a few applications to illustrate the potential usefulness of mathematical models in this field. Examples of flood-routing studies mentioned are a study of the Rhine at Karlsruhe and one of the Rhone above Lyons. The Rhine's hydraulic scheme features a number of hydro-power plants and that of the Rhone several weirs (Fig. 1 to 8). Under the heading of hydro-power development an example of a surge wave study arises in the problem of 'by the lockful' operation (Fig. 9 to 17). In this particular case, the implicit method could be used to reduce the computing time requirements, but it should be noted that the explicit one is preferable for cases involving more rapid operation. A scheme with power governed by water level is mentioned as a further example. It features a reservoir, a canal, a pressure tunnel with two surge tanks and a penstock. Turbine discharge is governed by reservoir level (Fig. 18.) Downstream and upstream boundary conditions remain permanently interdependent in this example. Mathematical models have also been used to study tidal propagation. Figures 19, 20 and 21 show the close agreement reached between observed and calculated data in a study of the Seine and the formation of a tidal bore which, if considered as a weak shock wave, can be dealt with by the explicit method. In a tidal propagation problem in a small river the downstream condition represents a floodgate system keeping the sea out at rising tide and opening at the ebb tide (Fig. 23). In a study of a cooling system for a thermal power station using water from the Loire and discharging it back to a shallow river arm the mathematical model features control sections at the ends of the river arm when the latter are high and dry at low water (Fig. 22). The various examples are merely mentioned as an illustration of the potential scope of mathematical models ; a brief discussion on numerical integration methods is given in an Appendix.