UNITED STATES DEPARTMENT OF AGRICULTURE 
Washington, D. C. April 23, 1924 
THE CAPILLARY DISTRIBUTION OF MOISTURE IN SOIL 
COLUMNS OF SMALL CROSS SECTION 
By W. W. McLaueuuiin, Senior Irrigation Engineer, Bureau of Public Roads. 
CONTENTS 
Page. | Page 
The principal results of the experiments..... 2 | Whittier and Riverside soils................. 1 
Results of previous experiments...........-- 3 | Santa Clara and Cache Valley soils......_._.- 14 
Experiments with soil columns of small cross Distribution of moisture in horizontal soil 
rameter ep ors iyh is sek [si sibaies: 3 Cdlagans 22st I SI See 16 
Plan of experiments jee od eee eee 5 | Distribution of moisture in tubes inclined 
Seale cntiay sail... 2222. 26 2.252252. ¥.-.--- 6 GowMward. «2225552 fsscc 350.222 eee 19 
idaodaactasi SOU: + ac, eares > eas 5+ 9) | SUMMALY 7. oe sates Jt - egw a oe gs Es 21 
In many of the irrigated sections of the west permanent ground 
water is present at or near the ground surface, frequently so near as to 
necessitate drainage before the lands can be cultivated successfully. 
In other instances the oround water is a factor in supplying moisture to 
plants or in alkali distribution. 
In either case it is essential to know how much water will be 
raised in the soil by capillarity to various heights from the ground 
water level, i. e., the vertical distribution of the capillary water. In 
the case of drainage this information is necessary in order to deter- 
mine how completely the soil may be dried out by under drains or 
open ditches when the ground w ater is lowered to a definite level. 
The extent of this drying out will in many cases influence the depth 
at which the drains will be placed. 
If, on the other hand, the field is to be irrigated and ground water 
known to be present, is counted upon to supply a part of the moisture 
required by the plants, it is necessary to hesioty the extent to which 
the supply will be drawn from the ground water, which again implies 
the necessity of some knowledge of the distribution of the water raised 
by capillary action. 
The rate of capillary movement was determined for several soil 
types in a series of investigations conducted by the author at River- 
side, Calif.!. The rate of movement is an important consideration to 
the irrigator, especially the rate of movement in a vertical direction. 
But the amount moved is of still greater importance. In the earlier 
experiments a difference was found in the amount of water required 
per inch of rise of the capillary moisture. It was found also that this 
1 Bulletin No. 835, United States ae of F Acetoultare: 
68319°—24-—_1 
