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Introduction, problems and approaches in sediment transport measurements

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This article is a summary of first chapter of the Manual Sediment Transport Measurements in Rivers, Estuaries and Coastal Seas[1]. This article gives an introduction of sediment transport, the contents of the manual, and sediment and erosion problems.

Introduction

In general the natural bathymetry (bottom configuration) of a hydraulic system is under the influence of a large number of factors varying from geological processes to the complex interaction of fluid and sediment particles. Most hydraulic systems can be considered to be in a state of dynamic equilibrium between deposition and erosion. The general characteristics only change very slowly with time. Human interference with the governing phenomena in such a delicate equilibrium will have morphological consequences. To predict these consequences for a specific project, it is of essential importance to have detailed knowledge of the local morphological variables such as the bed material size, the settling velocities of the suspended solids and the transport rates. To obtain this information, an extensive field survey should be carried out.

An important phase prior to the actual field survey is the selection of the most appropriate instruments, which usually is a rather difficult problem because a wide range of instruments has been developed from simple mechanical samplers to sophisticated optical and acoustical samplers. The selection of instruments is largely dependent on the variables to be measured, the available facilities (boat, winch) and the required accuracy. Especially, the required accuracy should be considered carefully. For example, a reconnaissance study requires the use of much less sophisticated instruments than a basic research study.

Contents of the manual

This manual provides information of all relevant aspects related to sediment transport measurements such as:

  • measuring principles and statistics,
  • type and accuracy of the instruments,
  • selection of the instruments,
  • analysis of the samples,
  • elaboration and presentation of the measuring results.

Any field worker knows that there is considerable difficulty and expense in sediment transport measurements inherent to the required time and labour in sampling of processes that usually vary greatly in space and time (see Wren et al., 2000[2]). Traditional forms of sediment transport measurements where samples are taken in the field and transferred to the laboratory for analysis may lead to inaccurate results (particle size). The importance of measuring particle size using sophisticated in-situ electronic instruments avoiding sample collection and handling which may change the particle size distribution (disturbing solids and/or aggregates), has been stressed by many field workers.

In this manual the attention is focused on those instruments which have been proven to be reliable and successful in field conditions. Instruments that are in a developing stage are not considered. Typical laboratory instruments are not considered.

Sedimentation and erosion problems in rivers, estuaries and coastal seas

Sedimentation and erosion engineering problems in rivers, estuaries and coastal seas are discussed as well as practical solutions of these problems based on the results of field measurements, laboratory scale models and numerical models.

Sedimentation and erosion problems

Human interference in hydraulic systems often is necessary to maintain and extend economic activities related to ports and associated navigation channels. Often, engineering structures are required:

  1. to stabilize the shoreline, shoals and inlets,
  2. to reduce sedimentation,
  3. to prevent or reduce erosion, or
  4. to increase the channel depth to allow larger vessels entering the harbour basin. Coastal protection against floods and navigability are the most basic problems in many estuaries in the world.

Sedimentation problems which generally occur at locations where the sediment transporting capacity of the hydraulic system is reduced due to the decrease of the steady (currents) and oscillatory (waves) flow velocities and related turbulent motions, are discussed. See also Coastal Hydrodynamics And Transport Processes.

Approach of sedimentation problems

The general approach to solve sedimentation and erosion problems is discussed. The topics are:

  1. Identification of the problem and wider context,
  2. Formulation of general objectives and desired state of knowledge,
  3. Determination of problem dimensions and analysis of physical system,
  4. Formulation of hypotheses related to the problem,
  5. Generation of alternative solutions and cost estimates,
  6. Selection of optimum solution.

The tools available for solving problems are discussed: existing databases, measurements and monitoring (field studies), numerical and or physical modelling. The manual focuses on measurements and monitoring.

See also

Summaries of the manual

Other internal links

External links

References

  1. Rijn, L. C. van (1986). Manual sediment transport measurements. Delft, The Netherlands: Delft Hydraulics Laboratory
  2. Wren, D.G., Barkdoll, B.D., Kuhnle, R.A. and Derrow, R.W., 2000. Field techniques for suspended sediment transport measurement. Journal of Hydraulic Engineering. Vol. 126, No. 2, p. 97104
The main authors of this article are Rijn, Leo van and Roberti, Hans
Please note that others may also have edited the contents of this article.