273


more water than the drained system; therefore the potential

for fluctuation is greater.

 Shown in Table 32 is the sum of simulated runoff and

simulated ET each year under predrainage and postdrainage

conditions. Except in dry years the total water loss is

greater under drained conditions than under undrained

conditions. In dry years, however, total water loss from

the system under primitive conditions exceeds water loss

under present conditions. This occurs because, in the

undrained system, water received during wet years is

carried over into dry years and becomes subject to ET a

year or more after it falls.

 Table 33 compares simulated total annual runoff and

simulated total annual ET under drained and undrained

conditions. Runoff is presented as percent of total annual

rainfall. ET is presented as percent of total annual

rainfall and also in inches. The carry-over of water from

wet years into dry years in the undrained system allows

simulated total annual ET to exceed total annual rainfall

in 1950-51, 1954-55, 1963-64, 1964-65, 1966-67, 1970-71,

and 1973-74. Total annual ET exceeds total annual rainfall

only in 1970-71 in simulations under drained conditions.

According to the simulations, runoff removes an average of

25% of yearly rainfall under present conditions, whereas

runoff is only 13% of yearly rainfall under primitive

conditions. ET is 77% of rainfall under present conditions

and 90% of rainfall under primitive conditions.