Showing papers on "River engineering published in 1998"

Internal and external validation of a two-dimensional finite element code for river flood simulations.

Abstract: While initial studies have demonstrated the feasibility of applying two-dimensional finite element models to reach scale river flood flows, the further development and practical use of such codes for engineering problems has been hampered by a lack of available validation data. This paper attempts to address this research need by conducting benchmark model validation studies over a range of reach scales, flow regimes and flood events. Specifically, four river reaches in the UK (the Culm, Stour, Severn and Blackwater) and one in the USA (the Missouri) have been modelled using the TELEMAC two-dimensional finite element scheme. These simulations have been compared in terms of the ability of the model to simulate both flood routing and stage hydrograph data at points internal to the modelled domain. This has enabled a more critical assessment of model capabilities to be obtained and has allowed the better definition of future research needs. In particular this study has identified the need to employ data internal to the model computational domain to achieve robust validation and the need to now undertake comparison of two-dimensional schemes with alternative flood simulation tools.

Surface erosion, sediment transport, and reservoir sedimentation

Abstract: Systematic plans and policies are needed to reduce adverse impacts of sedimentation and prolong the useful life of reservoirs. The ability to estimate the rate of watershed surface erosion, sediment transport, scour and deposition in a river system, and sediment deposition and distribution in a reservoir is essential to the development of sound sediment management plans and policies. The empirical Universal Soil Loss Equation has been applied in the eastern United States for the estimation of soil loss from agriculture land. The general application of this equation to other conditions remains questionable. A process based model for estimating surface erosion is needed. Most computer models for the stimulation and prediction of sediment transport in rivers and reservoirs are one-dimensional. Although truly two- or three-dimensi onal models are available, they require extensive field data for calibration and may be difficult to apply. A semi-two- dimensional model for water and sediment routing is an effective tool to solve river engineering problems. This paper provides a brief description of a systematic and integrated approach based on well established sediment transport equations, minimum energy dissipation rate theory, and the Bureau of Reclamation's Generalized Stream Tube model for Alluvial River Simulation (GSTARS 2.0). Examples of computed results are used to illustrate the applicability of different components of this approach.

River-management issues in Scottish rivers

Abstract: During recent years, there has been an increase in the use of‘alternative’or environmentally acceptable methods of river engineering and management. Most of the published information finds greatest application in lowland rivers where rates of fluvial process operation are slow; however, there is a lack of information relating to high-energy upland rivers. The paper presents the results of a consultative review of river-management problems in Scottish upland rivers. In addition, suggestions for good environmental practice relating to bank protection, fish-habitat improvement, flood alleviation and confluence realignment are discussed. Where appropriate, design guidelines are presented.

River engineering work on nanjing reach of lower yangtze river

Abstract: Through construction experience and research, including model tests, on the Nanjing reach of the lower Yantze River, it was found that different methods must be used to stabilize the discharge ratio of two branches around an island, depending on the length ratio of the two branches. When the two branches have a similar length, stabilizing the upstream bends is effective. When the length of one branch is longer than the other, stabilizing the head of the island will be most effective. A subsurface stone blanket of appropriate thickness has been the most popular type of revetment because of its resistance to flow scouring. A design method to determine the thickness of a subsurface stone blanket, how to launch stone to desired positions, and other innovations for improvement of the stone blanket revetment are discussed.

Der Zustand der Oberen Drau aus abiotischer Sicht: Defizite, Nutzungen

Abstract: This article discusses the present state of the Upper Drau River from an abiotic, river engineering, view point. An investigation of the existing flood protection structures has revealed insufficiencies for certain parts of settlements. Unlike the East Tyrolean section of the river downstream of the confluence with the river Isel, where flood protection structures were designed for the 100-year flood, many riverine areas in the Carinthian section are flooded already by 5 to 10-year floods. River bed degradation by more than one centimetre per year tends to underwash bank protection structures, causing increased maintenance costs.

CCP-correlation current profiler a comparison between laboratory and field measurements

Abstract: Over the last six years OCN, mainly as a subcontractor of RIKZ, has developed a new measurement method to determine high-resolution velocity profiles. High-resolution velocity profiles (both temporal order of seconds-and spatial-order of millimetres) can be determined in just the last meter(s) above the sea- or riverbed. Note that the last metre is of special interest since most sediment transport occurs in this distinct layer. The Correlation Current Profiler (CCP) measurement method has been proven accurate to within 1% with respect to laser Doppler reference measurements during tank trials. Coastal and river authorities are generally interested in availability of sediment transport measurement instrumentation for economical reasons (harbours, shipping), environmental reasons (pollution, river engineering) and safety reasons (flooding). Since the CCP measurement method is based upon acoustic backscatter strength, expansion of the CCP from a current measurement instrument to a transport measurement instrument seems obvious, and also turns out to be feasible. Apart from profiles, sediment structures in suspension as well as the morphology of the bed can be determined with the same instrument during the same measurement. Therefore, in September 1997 dredged river sediment has been put into a laboratory flume to simulate a typical Dutch river situation. Since glass walls permitted visual inspection of what was going on, the acoustically detected signature of the sedimentation processes and phenomena can be validated. Since the movement of sediment ripples is also acoustically determined, a closed mass balance between the effective bed motion and the suspended sediment transport will now be possible.