A General Procedure to Calculate Fall Velocity Over the Full Range of Sediment Sizes

Document Type

Thesis - Open Access

1987

Degree Name

Master of Science (MS)

Department / School

Civil Engineering

Alan L. Prasuhn

Abstract

It has long been recognized that the transport of sediment in water conveyance channels, such as rivers, streams and channels, is a serious and somewhat baffling problem. Not only does the transport of sediment affect the water quality and deposition in reservoirs, but it also indicates increased erosion. In addition, the energy given to the movement of sediment is a loss of energy from the water stream itself insofar as its flow rate is concerned. The movement of sediment is a complex prob1em. A number of methods have been deve1oped which compute sediment load. All of these formulae and methods depend on a number of sediment properties; the most significant being size of sediment particles, shape of sediment particles, specific weight of sediment particles, and fall velocity of sediment particles. Fall velocity may be defined as the velocity at which a sediment particle falls through a fluid. It is one of the primary factors in determination of sediment load. Fall ve1ocity is considered by many to be the most fundamental of these properties for a number of reasons. For instance, it is an indicator of a particles size and weight since the larger and heavier a particle is, the faster it falls through a fluid. It also can be useful in calculating retention times in settling basins and predicting the location of sediment deposits in a reservoir. “It has also been determined that the fall velocity of a particle is directly related to the stream velocity required to move particles along a stream bed. The most important application of fall velocity is its use in the previously mentioned formulae for computing sediment transport load”. It is the purpose of this thesis to analyze fall velocity and to present an improved computer program for the ca1culation of fall velocities for a wide range of temperature, specific gravity, shape factor and diameter. It will meet the following criteria: 1. Extension of the previous computer program giving accurate results for a wider range of particle size. 2. Testing of the extended computer program results against R.E. Slot equation introduced in this thesis. 3. Conversion of the previous computer program to operate in Microsoft BASIC for IBM PC. The general procedure for this study includes four major parts: 1. Reviewing current literature for existing theories and hypotheses, making a thorough evaluation of all questionable points in the analysis. 2. Providing a reasonable computer program to determine fall velocity of naturally worn particles. 3. Discussing and comparing the results, indicating the percent deviation among the methods used in the computer program. 4. Conclusion and recommendation for future study.

Streamflow velocity -- Computer programs

Sediment transport

application/pdf

88

Publisher

South Dakota State University

COinS