A transistor-equipped version of the 

 conductivity bridge would facilitate its 

 operation in the field because the standard 

 portable bridge is bulky and awkward to 

 pack. A transistor-equipped model is in 

 planning stages of development at the Fish- 

 eries Instrumentation Laboratory in Seattle. 



Percolation Test Procedure 



by the ratio found in step 1. 



8. Compare the resulting rate of dis- 

 placement with correlated apparent velocity 

 in the laboratory. 



DISSOLVED OXYGEN AND VELOCITIES IN GRAVEL 

 COMPARED WITH SPAWN SURVIVAL 



Using 5-minute dilution intervals in 

 the field, we found that five standpipes 

 can be worked together both efficiently and 

 effectively. With the extension of the 

 standpipe in position as previously de- 

 scribed, proceed as follows to determine 

 the rate of seepage in the streEimbed: 



1. Measure depth of water in the 

 standpipe, and from the known diameter, 

 compute the volume of water to be displaced. 

 The ratio between existing volume and 

 standard test volume is used to obtain dis- 

 placement rate in terms of measured velo- 

 cities in the laboratory. 



2. Evacuate the water from the stand- 

 pipe, open the valve to allow fresh water 

 to Seep in, close the valve, and record the 

 conductivity of the fresh seepage as refer- 

 ence for selecting the proper diluent curve, 

 (figure 5). 



3. Introduce into the standpipe a 

 Salt Solution in an amount sufficient to 

 bring the meter reading to approximately 

 1,000 ohras per centimeter cube, stir thor- 

 oughly, and record the exact reading. 



4. Open the standpipe valve, and 

 exactly 5 minutes later, close the valve 

 again, stir the water and take another read- 

 ing. Repeat procedure for four 5-minute 

 periods as illustrated in figure 11. 



5. Record the beginning and ending 

 conductivity readings, and correct them for 

 influence of temperature by the formula and 

 resistance coefficients (table 3) to correct 

 to 50° F. 



6. Subtract the "bleeding" value found 

 in the laboratory in still water from ending 

 conductivity reading. 



7. Apply the corrected beginning and 

 ending conductivity values to the graph in 

 figure 5. Using the proper diluent curve, 

 obtain the displacement number, and multiply 



The objective of the work at Mill Creek, 

 California, is to assess sources of egg mor- 

 tality under natural conditions, and to 

 determine what constitutes optimum natural 

 spawning and incubation environment. The 

 stcindpipe contributes to this program by 

 showing what seepage and oxygen requirements 

 are needed to sustain salmon spawn in natu- 

 ral streeim gravel. To fill in the necessary 

 points for plotting the unknown limits of 

 these requirements will call for numerous 

 Survival, seepage, and oxygen comparisons. 

 The reliability of the ensuing plot will 

 undoubtedly be improved with increased num- 

 bers of such tests. 



At the present stage of progress the 

 picture is complicated by three interrelated 

 Sources of mortality in the gravel resulting 

 from deficiencies in oxygen and seepage: 

 deficiencies in the level of dissolved oxy- 

 gen, the delivery of oxygen, and the cleans- 

 ing of waste products. Two of these, well- 

 defined by Wicket (1954), involve delivery 

 of oxygen to the eggS; in his words, "gross 

 supply is QDO". In this formula (Q) equals 

 the volume of water (per unit of time) 

 delivering oxygen to the eggs and (DO) is 

 the oxygen (per unit of volume) dissolved 

 in the water. Mortality, then, may result 

 from either critical oxygen levels or in- 

 adequate seepage to introduce oxygen to the 

 eggs. 



A third source of mortality, described 

 by Wolf (1957 a, b) in his hatchery research on 

 blue-Sac disease, may result from one of 

 these factors alone. The eggs may become 

 enveloped by a film of their own metabolic 

 waste which is not washed away by seepage 

 or free water movement. Wolf states as 

 follows: "The kidney may be pumping its 

 products against increased osmotic pressure. 

 If it is severe enough, death results; 

 intermediate severity results in damage — 

 blue-Sac disease." It follows from this 

 that the very same things may occur in the 

 natural gravel environment, i.e., loss of 

 eggs from their own metabolic products. 



17 



