INTRAGRAVEL FLOW AND INTERCHANGE OF WATER IN A STREAMBED 



BY Walter G. Vaux, Chemical Engineer, Bureau of Commercial Fisheries Biological Laboratory, 



AUKE Bay, Alaska 99821 



ABSTRACT 



The chemical quality of intragravel water in streams — 

 the environment of salmon eggs, embryos, and alevins— 

 is influenced by the rate of interchange of stream water 

 and intragravel water. Factors controlling the direction 

 and magnitude of flow or interchange of this water 

 were identified in this study. Equations describing 

 motion of waterflow within the streambed under 

 specified boundary conditions are developed, and tests 

 of the mathematical model with an electrolytic bath 

 analog model are described. 



The direction of waterflow within a streambed and 

 the interchange of water between the bed and the 

 stream depend primarily on the permeability, depth, 

 and longitudinal profile of the porous streambed. 

 Water upwells where permeability or depth of gravel 

 decreases in the direction of streamflow and where the 

 longitudinal bed profile is concave. Water downwells 

 where permeability or depth of gravel increases in the 

 direction of streamflow or where the longitudinal bed 

 profile is convex. 



Embryos and alevins of Pacific salmon (genus 

 Oncorhynchus) live in gravel beds of streams for as 

 long as 9 months before the fry emerge. The young 

 salmon may be subjected to a poor chemical en- 

 vironment because of the low waterflow in the 

 spawning bed. In laboratory experiments, oxygen 

 privation and reduced waterflow, alone or to- 

 gether, impaired growth and development of 

 salmonid embryos and caused mortality (Silver, 

 Warren, and Doudoroff, 1963; Shumway, Warren, 

 and Doudoroff, 1964). In natural streams, mor- 

 tality of salmon spawn was high when the supply 

 of dissolved oxygen in intragravel water (water 

 occupying interstices within the streambed) be- 

 came low (Phillips and Campbell, 1962; McNeil, 

 1966). Dissolved waste metabolites are known to 

 be harmful to fishes: high levels of free carbon 

 dioxide reduce the blood's affinity for oxygen, and 

 un-ionized ammonium hydroxide is highly toxic 

 to alevins (McNeil, WeUs, and Brickell, 1964). 

 The concentration of waste metabolites in the 

 water surrounding organisms generating the wastes 

 varies inversely with the rate of flow of intragravel 

 water. It is, therefore, necessary that the velocity 

 of intragravel flow be adequate to assure low con- 

 centrations of waste metabolite. 



Published March 1968. 

 FISHERY BULLETIN: VOL. 66, NO. 3 



Because the primary source of oxygen and the 

 water flowing through the gravel in many salmon 

 spawning beds is stream water, the processes that 

 regulate interchange between intragravel water 

 and stream water are important in the ecology of 

 sahnon spawning beds. The purpose of my study 

 is to identify some of the variables that control 

 this interchange. In an earlier paper (Vaux, 1962), 

 I related the direction of interchange to streambed 

 shape from a mathematical model and presented 

 field data which demonstrated that the relation 

 was correct. 



This paper treats the theory of flow of intra- 

 gravel water in detail and gives the results of my 

 laboratory experiments in which intragravel flow 

 and interchange were simulated with an analog 

 model. The means by which interchange can be 

 controUed to improve water quality within salmon 

 spawning beds are discussed. 



I started my study of the movement of water 

 within streambeds in 1958 whUe employed at the 

 Fisheries Research Institute of the College of 

 Fisheries, University of Washington. The experi- 

 mental work and some of the mathematical form- 

 ulation were completed in 1960-61 as part of a 

 thesis, which was submitted to the Department 



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