56 THE FUTURE OF ARID LANDS 
wells have for years been used to supply water for small holdings. 
The aquifer consists of sand layers with a water table at 40 to 
60 feet in ample quantity, and so a tube well scheme has been 
initiated. How successful this will be remains to be seen because 
percolation is heavy and evaporation, with summer temperatures 
up to 120°F. is high, but it is hoped that each well can irrigate 
150 acres. Early in 1954 Australia supplied tube wells to the 
TDA under the Colombo Plan. 
It seems safe to prophesy that in perhaps a decade there will 
be need to study a salt problem in parts of the Thal, and FAO 
is already at work in Pakistan on this problem in the Indus valley. 
In arid and semi-arid areas where the need for recharging the 
underground water is acute there are often long periods of no 
rain, interspersed with short bursts of storm rains with extremely 
rapid runoff, carrying astonishing quantities of surface material 
of sizes ranging from silt particles to boulders. These storm waters 
are gone in a relatively short time, and the problem is how to 
make good use of what are sometimes quite large supplies, by 
spreading and slowing down the rush of waters, by the use of 
dams and tanks, by selection of the site for percolation, and so on. 
It is impossible in this composite paper to do more than indicate 
the complexity of the problems concerning water supplies. The 
U. S. Geological Survey has prepared a list of thirty ground water 
problems needing research, and in arid areas the general problem 
of the development of water resources to the fullest economic 
capacity will always be a vital one. 
Salinity Problems 
Rainfall is relatively free from salts, and where rainfall is 
adequate for agricultural production excess soluble salts in the 
soil are leached away in the drainage water, but where rainfall is 
low, leaching is reduced and salt accumulation can occur. All 
irrigation waters contain salts dissolved from the rocks and soils 
through which the water moves. Some years ago Scofield studied 
irrigated areas in this part of the United States and described the 
salt balance as the relation between the amount of salts being 
delivered in irrigation water and the amount removed from the 
