Dae, ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
water shortages and destructive floods. Although enormous sums 
have been spent on flood control, complete protection from floods is 
difficult and often prohibitively costly, and in only a few places has 
it been accomplished. 
Whatever conclusions are reached with regard to the economics of 
flood control by storage reservoirs, from the standpoint of conservation 
of water supply it is advantageous to salvage as much of the floodwater 
as possible. In certain areas where water supply is now inadequate, 
as it is in many places west of the 100th meridian, much of the water 
from precipitation escapes to the sea during floods. In Los Angeles 
County, Calif., much of the floodwater is retained in surface reservoirs 
from which it is later discharged into specially prepared recharge 
basins and seeps into the underground aquifers. Some of the flood- 
water is caught in seepage reservoirs designed to promote infiltration 
into the ground-water basins, and some of it escapes to the sea, but 
essentially all the floodwater in the Los Angeles area will be put to 
beneficial use when the projects now under consideration are com- 
pleted. Plans for similar flood control in other parts of the country 
are in various stages of execution. 
Ground water and surface water are so intimately related that for 
proper solution of the over-all problems of water supply, control, and 
conservation it is now necessary to have all the facts regarding both. 
Precipitation, which is the source of both, is partly lost, largely through 
evaporation. Especially during the growing season, a large part 
enters the ground and is transpired by plants. The remainder per- 
colates downward below the plant roots to become ground water, or 
runs off directly as surface flow. The ground water, returning to the 
surface as seeps or springs, provides the base flow of the streams which 
prevails through periods of low precipitation, On the other hand, 
especially in the West, many streams lose water by seepage in certain 
stretches and thus recharge the ground-water reservoirs. 
Many of the basic ground-water investigations in the United States 
are carried on cooperatively by the United States Geological Survey 
and State or local agencies, including State geological surveys, State 
engineers, counties, and municipalities. In Illinois ground-water 
investigations are made by the State Geological Survey and the State 
Water Survey; and in Missouri investigations are made by the State 
Geological Survey. In California a large staff of engineers in the 
State Division of Water Resources for many years has been investi- 
gating overdraft of ground-water supplies. Recently arrangements 
were made whereby the United States Geological Survey, in addition 
to its investigations in Los Angeles, Orange, and Santa Barbara 
Counties, will assist the Division of Water Resources in the geological 
phases of a State-wide inventory of the water resources of California. 
