40 80 120 160 



Permeability of streambed grovels fcm./minj 



Figure 4. --Observed relationships reported by Wickett 

 (1958) between permeability of spawningbeds andsur- 

 vival of pink and chum salmon tcD the migrant fry stage. 



Method of Measuring Permeability 



The coefficient of permeability describes the 

 facility with which a liquid can flow through 

 permeable materials. Since viscosity affects 

 the rate at which a liquid flows, it is common 

 practice to express permeability at a temper- 

 ature selected as a standard (68° F. was se- 

 lected in these studies). 



The coefficient of permeability (k) is defined 



as 



k = 



Ai 



where Q is the volume of water flowing per 

 unit of time through a gravel bed having a 

 hydraulic gradient i and a cross-sectional area 

 A. Since i is dimensionless, the dimensions 

 of k are 



length 

 time 



Samples of bottom materials were collected 

 from two streams. Each sample consisted of 

 two 6-inch-diameter cores that were removed 

 from adjacent points in important pink salmon 

 spawning areas. Size composition was deter- 

 mined, and each sample was thoroughly re- 

 mixed and divided into 12 fractions. The frac- 

 tions were added one at a time to a constant- 

 head permeameter (fig. 5). 



To attain a relatively uniform degree of 

 compaction (and porosity), gravel was neither 



/f 



Inlet 



J, 



Overflow, 



T^ 



Q measured 

 at outlet 



<^ Bottom 

 sample 



i^^rJ 



-5 dia. 



v:^- 



■M. 



r 



Ah 



Hi" 



I 



Figure 5. — Constant-head permeameter used to meas- 

 ure permeability ofspawning bed materials. Hydraulic 

 gradient (i)= A h/1. 



tamped nor shaken after being placed in a 

 permeameter. Hence, the permeabilities 

 measured were most likely representative of 

 loose, unconsolidated spawning bed materials. 



The coefficient of permeability was meas- 

 ured for 19 bottom samples. Water was allowed 

 to pass through each sample continuously over 

 the period August 25-30, 1960. Permeability 

 of each sample was measured August 26, 29, 

 and 30. Water temperature varied from 49° to 

 56° F. at the times measurements were made, 

 and all permeability readings were corrected 

 for standard viscosity of 1.0 centipoise at 

 680 F.' 



Results of Permeability Tests 



A good inverse relationship was found be- 

 tween the coefficient of permeability and the 



^ Each observed value of permeability was multiplied 

 by water viscosity (iii centipoises) at the temperature 

 a measurement was made to obtain permeability at 68° 

 F. (see Frevert and Kirkham, 1948). 



