Showing papers on "River engineering published in 2000"

Holocene development of the River Lippe valley, Germany: a case study of anthropogenic influence

Abstract: The characteristics of the Holocene valley floor of the River Lippe, Germany, are atypical for a river in central Europe. The valley floor consists of three terrace levels, which are not always clearly separated from each other. Analysis of the sediments making up the terraces indicates that they accumulated during the course of the entire Holocene, although there is insufficient information available to allow detailed determination of phases of fluvial change and stability responsible for terrace formation. Two of the terraces exist only in the lower reaches of the valley, where they converge and diverge with the third. The lowest terrace consists only of a narrow strip, running parallel to the river channel. The configuration of the valley floor may be explained by a series of anthropogenic influences. The earliest human impact probably occurred about 2000 years ago when, during their campaign against German tribes, the Romans built a towpath and may have changed the channel planform from its natural, anabranching pattern to a meandering form by building small dams on local distributary forks. Implementation of artificial meander cut-offs to improve navigation on the river began in medieval times. The morphological response to these human interventions was primarily degradational. In the 19th century, artificial lateral fill was used to narrow the channel and the towpath was renewed several times. The trace of the most recent towpath is still discernible as a narrow strip parallel to the river channel, and it constitutes the lowest terrace level. Comparison between the bankfull discharge of a 4000-year-old abandoned channel and the formative flow for the modern channel supports the premise that, prior to anthropomorphic influence, the natural planform was anabranched. Copyright © 2000 John Wiley & Sons, Ltd.

The Sarawak River barrage—hydrotechnical and geotechnical aspects

Abstract: Studies conducted over the last ten years have resulted in the construction of a lock and barrage on the Sarawak River in the state of Sarawak, Malaysia. The barrage controls river and tidal flows and has eliminated most of the tidal variation in water level which was formerly experienced in Kuching, the state capital of Sarawak. This paper reviews the hydrotechnical and geotechnical studies of the river and outlines the current operation and effects of the barrage.

User's Primer for BRI-STARS (BRIdge Stream Tube model for Alluvial River Simulation)

Abstract: BRI-STARS (BRIdge Stream Tube model for Alluvial River Simulation) model is a generalized semi-two-dimensional water and sediment-routing model with an integrated graphical interface for solving complicated river engineering problems with limited data and resources. This model is capable of computing alluvial scour/deposition through subcritical, supercritical, and a combination of both flow conditions involving hydraulic jumps. Unlike conventional water and sediment routing models, it is also capable of simulating channel widening/narrowing phenomena as well as local scour due to highway encroachments. It contains a subset of the Federal Highway Administration's WSPRO subroutines for computing bridge hydraulics. This User's Primer provides a brief description of the BRI-STARS model, installation and operation guidelines, the usage of the various utility programs within the package, and an example application of the model. Detailed instructions for the use of utility programs included in the BRI-STARS package including their menu structures and their operations are given.

Fluvial geomorphology and river management

Abstract: Australian river landscapes offer many challenges for management. Much Australian river research is novel, but practical concerns have always had an influence on the research agenda. Australia’s distinctive contributions to fluvial geomorphology include recognition of the great age of many fluvially eroded landscapes; understanding complex levee, terrace and valley fill sequences; analysing the impacts of rare major floods; interpreting the effects of impoundment, mining and urbanisation; and understanding the great anastomosing inland river systems. River restoration is now a major theme in the literature of river engineering, fluvial geomorphology and landscape design. Great achievements are occurring in geo-ecological river management and engineering. Changing people’s thinking is becoming at least as important as gaining new scientific knowledge. The existing understanding needs to be more widely shared and enhanced by greater involvement with Asian countries where river management issues daily affect the lives of millions of people.

Sediment Transport in the Lower Mississippi River

Abstract: : The Lower Mississippi River, extending from Cairo, Illinois to the Gulf of Mexico, annually transports approximately 170 million tonnes of sediment. Historically, the quantity and calibre of sediment derived from catchment erosion have been affected by changes in land-use and management. For example, soil erosion increased during the 19th and early 20th centuries due to settlement by Europeans and this may have elevated catchment sediment supply to the Mississippi River, while more recently the supply of sediment from tributaries is known to have decreased markedly as a result of river engineering and management. Specifically, the construction of large dams as part of the Mississippi River and Tributaries (MRT Dardeau and Causey, 1990). However, a case can be made that the bed material load must have increased since the 1940s. This argument is based on analysis of morphological changes observed along the river that have led to an overall increase in slope and available stream power, coupled with the fact that bed material sizes along the river have remained almost constant.

Optimum design of large flood relief culverts under the A89 motorway in the Dordogne—Isle confluence plain

Abstract: The planned A89 motorway will go through the Dordogne — Isle confluence plain, which is regularly flooded under the effect of both river discharges and ocean tides. Hydraulic transparency of the motorway embankment was one of the prerequisites imposed by the French government. In order to optimize the cost/efficiency ratio of large culverts located under the motorway, their position and size had to be determined with great accuracy. This task has been fulfilled thanks to complementary sophisticated physical scale models and 2-D numerical models. The schematization principles adopted in the 2-D numerical model concerning bridge pier grouping were validated using the physical scale model. The finite element TELEMAC-2D code was used to draw up the optimum design of this river engineering scheme. TELEMAC-2D solves the 2-D Shallow Water equations on non-structured grids in the presence of alternately dry and wet beds. The 2-D numerical modelling based on high quality topographic data allows considerable improvements to be made in the computation of flood flows in a flat valley, as compared with traditional one-dimensional techniques. Near flood relief culverts in particular, the various physical effects contributing to the overall head loss can be distinguished: bottom roughness, medium size bed variations, strong curvature of the streamlines and vortices behind abutments. The hydraulic impact of the optimum solution has been studied under different aspects (rise of maximum flood levels, increase in maximum velocity, changes in the water flow patterns, submersion time of flooded land, modification of flood routing characteristics) for a wide range of flood hydrological events. Copyright © 2000 John Wiley & Sons, Ltd.

Managing River Environments

Abstract: 1. Introduction 2. Understanding the dynamics of river environments 3. Traditional river engineering approaches to river management 4. Consequences of traditional river engineering 5. Revised approaches to river engineering 6. Managing river environments into the future Appendices Bibliography Index

Evaluation of an alternative way of river bank protection in the Meghna Estuary

Abstract: After the disastrous floods in Bangladesh in 1987 the Flood Action Plan (FAP) was initiated. The FAP was a co-ordinated action to study the flood problems of Bangladesh. The Meghna Estuary Study (MES) was drawn up as a component of the FAP. The overall goal of MES is to ensure the physical safety and social security of the people living in the coastal areas and on the islands of the Meghna Estuary. This goal is to be realised by retaining and increasing knowledge of the hydraulic and morphological processes and by developing appropriate techniques for efficient land reclamation as well as effective river bank protection. In particular during the monsoon season erosion of the river banks occurs throughout the Meghna Estuary. The erosion causes direct land loss (including loss of livelihood and impoverishment) and, where embankments are eroded, results in flooding of homesteads and agricultural land. Looking at the planform development of the Lower Meghna it is expected that in future years the eastern river bank of the Lower Meghna river starting south of Chandpur up to Haimchar is going to be subject to severe erosion. The river banks are highly erosive due to the non-cohesiveness of the sediments, the small particle size and the high flow velocities. Previous studies carried out have shown that protection of the river bank using conventional river bank protection methods is not generally economically viable at the current level of economic development in Bangladesh. It is expected that at the current level of economic development in Bangladesh alternative Iow cost bank protection measures are the only viable option to protect the river banks against erosion on a large scale. Nevertheless it must be stated that the circumstances are severe and the possibilities and necessary know-how have to be assessed by further research and execution of experiments. Under MES several pilot projects have been executed to study alternative ways of river bank protection. In part I of this study the author has studied the application of flexible bottom screens in combination with permeable spurs. In part II the application of bottom screens to create a roughness field is subject of discussion. Both studies are conducted under the responsibility of the Technical University Delft. One of the pilot projects executed by MES is the Hanar Char erosion control pilot scheme in which flexible bottom screens and permeable spurs are applied as an alternative way of river bank protection. This pilot scheme was executed from March to July 1999 and is part of the proposed Haimchar erosion control pilot project, which covers the complete eastern river bank from Chandpur up to Haimchar. However, up till August 2000 only a part of the Haimchar erosion control pilot project has been executed. The objective of this study is to determine whether flexible bottom screens and permeable spurs are an effective way of river bank protection in the river dominated part of the Meghna Estuary. This is done by studying the available literature and the influence of the structures on the flow pattern and morphology. Flexible bottom screens Flexible bottom screens show great analogy with so called bottom vanes which are placed at a certain angle of attack with the flow. The vanes cause the passing flow to attain a circular motion downstream from it. The sediment-rich bottom flow is directed to the river bank and the erosive upper current is directed towards the centre of the river. In the available literature on bottom vanes the distinction is made between vanes placed at a small angle of attack with the flow and vanes placed at a high angle of attack with the flow.

Channel Restoration Design for Meandering Rivers (CD-ROM)

Abstract: : ELECTRONIC FILE CHARACTERISTICS: 15 MS Word documents PHYSICAL DESCRIPTION: 1 computer laser optical disc (CD-ROM); 4 3/4 in; 303MB SYSTEMS DETAIL NOTE: IBM-clone PC-compatible ABSTRACT: A framework for channel restoration design is presented The approach bridges the gap between simplistic designs based on reconnaissance level, geomorphic appraisals and detailed designs requiring advanced numerical modeling of system hydro-dynamics and sediment transport processes Re-establishing equilibrium between the sediment supply and available sediment transport capacity provides the primary objective of the design framework as this is essential to production of a restoration design that is sustainable without the need for heavy maintenance A geomorphic engineering approach is used, that recognizes that the river is the best restorer of its natural morphology and seeks to employ fluvial processes in restoration through prompted recovery' The techniques employed in the design approach mix empirical-statistical and analytical (process-based) methods to produce reliable solutions System variability is taken into account at reach and local scales as this is a primary feature of natural meandering channels that must be replicated in a restored river Hence, confidence limits and discretion zones are included in design tools The restoration design method presented here is not a cook book' procedure, but provides a framework within which the sound judgement of practitioners with experience in river engineering can be applied