WATER RESOURCES 197 
detergents, not oil, are familiar polar compounds. A monomolec- 
ular layer, if it could be maintained, would have the effect of 
greatly reducing reservoir evaporation, but its harmful effects, if 
any, are unknown, and must be carefully studied before seriously 
considered for use. 
Reforestation, controlled livestock grazing, regulated recreation, 
and other accepted practices to avert land erosion have the addi- 
tional main purpose of conserving water. The saving of valuable 
land and water resources is a goal in itself, but an attendant 
benefit is the reduction in the volume of sediment poured into 
stream beds. Sediment is a tremendous nuisance, as it reduces 
water quality, aggrades channels, makes deposits on cultivated 
fields during irrigation, and shortens the life of reservoirs. In 
planning projects in areas where sediment is a serious problem, 
adequate consideration, from the physical and financial view- 
points, must be given to sediment problems. 
One of the important measures needed for putting our water 
supplies to most beneficial use is improved hydrological tech- 
niques and more comprehensive hydrological and meteorological 
data. The installation of additional observation and recording 
stations during recent years and the accumulation of records 
covering longer periods will pay off in terms of more accurate 
planning of engineering structures. Recent improvements in 
methods for computing maximum probable large and small floods, 
together with more precise hydrological data, provide a firmer 
basis for saving water. 
More accurate estimates of water yield from snow cover will 
result in improved operation of irrigation projects. The precision 
of flood control operations can be enhanced by better estimates of 
the rate of runoff from snow melt. An illustration of the benefits 
of better data lies in the research completed and underway at Lake 
Hefner, Lake Mead, and the Bruning Air Base which is providing 
more precise methods for estimating evaporation and transpira- 
tion. These are aids toward more exact use of reservoir capacity, 
irrigation, and operating methods. 
Evaporation is a major waster of water, but is not first in this 
unenviable distinction. Evaporation consumes an estimated 15 
