28 DIVISION OF WATER RESOURCES 



The climatic conditions at this point are representative of the 

 coastal climate of southern California. Summers are warm and dry 

 while winters are moderate. Coastal fog's are of frequent occurrence 

 and tend to modify evaporation from water surfaces and transpiration 

 losses by plants. 



Soil at the station is of alluvial origin, classified as Ilanford fine 

 sandy loam which grades into coarse yellow sand at a depth of 6 to 

 7 feet.* It is probably lacking' in humus and contains a small amount 

 of alkali although not enough to affect the growth of the type of vege- 

 tation under investigation. An ample supply of good water for use 

 in the experiment tanks was found at a depth of a few feet. 



Station Equipment 



The equipment first installed early in 1929 consisted of 12 soil 

 tanks, each connected to a IMariotte supply tank, a set of maximum 

 and minimum thermometers and a thermograph set in an instrument 

 shelter, a standard rain gage, a standard Weather Bureau evaporation 

 pan, a circular sunken evaporation tank of the same diameter as the 

 soil tanks and a shallow well with a hand pump to supply water for 

 the various tanks. Later, two anemometers and three additional soil 

 tanks with Mariotte control were added, making 15 soil tanks in all. 



Soil tanks are of the double type with an annular space between 

 the inner and outer shell. The inner tank, 23^^ inches in diameter by 

 6 feet in depth, is suspended in the outer tank by means of a heavy 

 angle-iron rim around the top. The bottom of the inner tank is 

 removable and bolted in place by long rods to the supporting top rim. 

 The inner tank holds soil, and the outer is a reservoir for water Avhich 

 passes into the soil through perforations in the tank wall and in the 

 bottom plate. Each soil tank unit is connected by a pipe to a INIariotte 

 supply tank which regulates the height of the water table in the 

 annular space between the inner and outer tank walls and supplies 

 water to the tank growth as needed. 



From time to time additional tanks of simple construction were 

 added in which tules, cat-tails, willows and wire rush were grown in 

 order to measure consumptive use of water by each variety. One tule 

 tank and one tank for willows were each 6 feet in diameter by 3 feet 

 deep. Smaller tanks, used for other swamp growth, were each 25 1 

 inches in diameter by 2.7 feet deep. Each of the 6-foot tanks used 

 water in such quantities that it was necessary to provide them with 

 supply tanks equipped with automatic feed control to provide watey as 

 needed, and at the same time hold the water level in the crop tank at 

 a constant level. This could have been accomplished by i\Iariotte con- 

 trol, but in this case a needle valve operated by a float was found 

 satisfactory. When the water surface in the crop tank dropped, due 

 to transpiration and evaporation losses, the float dropped also, opening 

 the needle valve and admitting more water. When the water surface 

 returned to its original level, the valve closed and the flow ceased. A 

 water glass and a graduated scale on the side of tlie supply tank 

 allowed readings of amounts of Avater Avitlidrawn. This type of control 

 has been in use at all three stations during the investigations. 



* Soil Survey of the Analiiim Area. California. Bureau of Soils, U. S. Depart- 

 ment of Agriculture. 



