THEORETICAL DISCUSSION AND LABORATORY 

 CALIBRATION OF THE STANDPIPE 



As we have seen, the water seeping 

 through the gravel of the streambed must 

 contain dissolved oxygen if the spawn is to 

 Survive. If the level of oxygen is to be 

 adequate, a fresh supply of oxygen- be axing 

 water must displace depleted water. 



During the extended period of incuba- 

 tion of the eggs, the amount of seepage 

 usually declines from the original cleansed 

 condition of the redd because the migration 

 of fine particles closes pores in the 

 gravel of the streambed. On the other hand, 

 turbulence of the water over the redd tends 

 to remove these fine particles and to im- 

 prove seepage, thus resulting in a fluctu- 

 ating pattern of seepage, as has been 

 pointed out by McDonald and Shepard (1955). 



The best method found for observing 

 these changes in seepage at Mill Creek is 

 the standpipe method presented in this 

 paper. With this method, seepage rate is 

 associated with the rate of displacement of 

 water in the chamber of the standpipe buried 

 in the streambed. 



To measure the exchange of water in 

 the standpipe chamber, Wickett (1954), 

 Pollard (1955), and Terhune (1957) insert a 

 dye and compare changes in its coloration 

 with standard dilutions of the dye. In the 

 Mill Creek work, a weak solution of salt 

 and a portable conductivity bridge is used 

 to detect this exchange. Here, the struc- 

 ture of the Mill Creek standpipe facilitates 

 measurements by its ability to open and 

 close, making possible both (1) precise 

 timing of the dilution interval and (2) 

 stirring of the salt solution without un- 

 natural washing. With the use of the sen- 

 sitive conductivity bridge, the slowest 

 movement of groundwater is measurable. 



Theoretical Discussion 



The problem of correlating laboratory 

 tests with field tests has been pointed out 

 by Burmister (1954): "In principle, deter- 

 mination of the permeability of soil is 

 quite simple. However, due to natural vari- 

 ations of material in place, it is often 

 difficult to relate tests on small to large 

 masses. In sampling soil it is hard to 

 prevent disturbing the density and structure 

 of the material. Chjtnges in chemical and 



organic content of the permeating fluid can 

 cause differences. Migration of particles 

 may occur both in the field and laboratory. 

 While some variables can be arbitrarily 

 controlled or eliminated in the Ijiboratory, 

 it is often necessary to consider them in 

 the field application." 



The laboratory test is based on the 

 formulations of Hazen (1893) and Poiseville 

 (1846), who found that the velocity of flow 

 in capillary tubes is proportional to the 

 slope of the hydraulic gradient. Darcy 

 (1856), Fancher and Lewis (1932), Fishel 

 (1935), and Burmister (1954) confirmed the 

 application of this principle to rates of 

 flow in uniform sands. The formula, re- 

 ferred to as Darcy's Law, expresses this 

 flow in the following: 



L = length of drop section 

 (fig. 3) 



H/L = hydraulic gradient 



In addition to the factors given in 

 the above formulation, other factors must 

 be considered. Fair (1934) states in this 

 regard: "Starting from the well-known 

 formula for flow of water through pipes, a 

 rational expression of the flow of water 

 through Sand was obtained by regarding the 

 pore spcice of sand as a series of tubular 

 passages through which water flows in much 

 the same way as it does through intercon- 

 nected pipes. The factors that enter into 

 the formula are the frictional resistance 

 of Sand, the velocity and temperature of 

 water passing through it, the void space 

 through which the water flows, and the size, 

 shape, and packing of the sand ..." 



The formula for flow of water through 

 pipes has been discussed. The expressions 

 "turbulent" and "Iciminar" in reference to 

 flow involving frictional resistance are 

 commonly used and are explained in table 1, 

 which is taken from the work of Burmister 

 (1954). 



Observations indicate that the flow of 

 water in the gravel at Mill Creek may be 

 either turbulent or laminar, but since this 



