Citation
Fischer, Hugo Breed (1966) Longitudinal dispersion in laboratory and natural streams. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:09292015082820697
Abstract
This study concerns the longitudinal dispersion of fluid particles which are initially distributed uninformly over one cross section of a uniform, steady, turbulent open channel flow. The primary focus is on developing a method to predict the rate of dispersion in a natural stream.
Taylor's method of determining a dispersion coefficient, previously applied to flow in pipes and twodimensional open channels, is extended to a class of threedimensional flows which have large widthtodepth ratios, and in which the velocity varies continuously with lateral crosssectional position. Most natural streams are included. The dispersion coefficient for a natural stream may be predicted from measurements of the channel crosssectional geometry, the crosssectional distribution of velocity, and the overall channel shear velocity. Tracer experiments are not required.
Large values of the dimensionless dispersion coefficient D/rU* are explained by lateral variations in downstream velocity. In effect, the characteristic length of the cross section is shown to be proportional to the width, rather than the hydraulic radius. The dimensionless dispersion coefficient depends approximately on the square of the width to depth ratio.
A numerical program is given which is capable of generating the entire dispersion pattern downstream from an instantaneous point or plane source of pollutant. The program is verified by the theory for twodimensional flow, and gives results in good agreement with laboratory and field experiments.
Both laboratory and field experiments are described. Twentyone laboratory experiments were conducted: thirteen in twodimensional flows, over both smooth and roughened bottoms; and eight in threedimensional flows, formed by adding extreme side roughness to produce lateral velocity variations. Four field experiments were conducted in the GreenDuwamish River, Washington.
Both laboratory and flume experiments prove that in threedimensional flow the dominant mechanism for dispersion is lateral velocity variation. For instance, in one laboratory experiment the dimensionless dispersion coefficient D/rU* (where r is the hydraulic radius and U* the shear velocity) was increased by a factory of ten by roughening the channel banks. In threedimensional laboratory flow, D/rU* varied from 190 to 640, a typical range for natural streams. For each experiment, the measured dispersion coefficient agreed with that predicted by the extension of Taylor's analysis within a maximum error of 15%. For the GreenDuwamish River, the average experimentally measured dispersion coefficient was within 5% of the prediction.
Item Type:  Thesis (Dissertation (Ph.D.))  

Subject Keywords:  Civil Engineering  
Degree Grantor:  California Institute of Technology  
Division:  Engineering and Applied Science  
Major Option:  Civil Engineering  
Thesis Availability:  Public (worldwide access)  
Research Advisor(s): 
 
Thesis Committee: 
 
Defense Date:  20 May 1966  
Funders: 
 
Record Number:  CaltechTHESIS:09292015082820697  
Persistent URL:  http://resolver.caltech.edu/CaltechTHESIS:09292015082820697  
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided.  
ID Code:  9180  
Collection:  CaltechTHESIS  
Deposited By:  Leslie Granillo  
Deposited On:  30 Sep 2015 15:42  
Last Modified:  30 Sep 2015 15:42 
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