IOWA ACArrEMY OF SCIENCE 
153 
related to the control of river flows and flood plain reclamation. Im- 
agine observing from a balloon, Nature would show us an area, with 
many ponds and lakes, which catch and hold the rainfall within the 
water-shed. Only the overflow, and that which falls within the immed- 
iate water-shed of the river, contributes to the increase of river flood 
flow. In the times of the prairie, before the plow had broken the sur- 
face, rendering it more penetrable by the rain, floods were common, as 
evidenced by the deposits on the river flats and the meandering courses 
of these rivers. Deposits of soil eroded from the water-shed were, in 
these earlier days, comparatively small. Many of the rivers had clear 
water and pebbly bottoms. Since cultivation, conditions are so changed 
that more of the rainfall is absorbed directly by the soil. Floods have 
not been so frequent because the run-off is reduced, but those which do 
occur have been more destructive in their nature, carrying the loosened 
soil, to fill the channels and obstruct the flow, driving it out over the 
river flats. 
The part played by these upland ponds and by the lakes, marshes and 
swamps, has been to catch and hold back much of the rainfall from 
causing floods in the river. Destructive floods, caused by rainfall alone, 
have been infrequent until within the past ten years, excepting within 
special sections. An illustration of these floods may be found in the 
year 1906. If dates are not mixed, the month of April was peculiarly 
dry. In May the rains early became excessive, lasting on until about 
the 10th of June. During the early part of May, it was frequently re- 
marked by farmers and other observant men, that the ground took 
care of all the rainfall in excellent manner, the roads remaining good 
and drying rapidly within a few days. These conditions continued until 
the first week in June, when it was observed that ponds were beginning 
to fill, and the roads would no longer dry. During the first ten days of 
June, of almost continuous rainfall, all of the ponds and every depres- 
sion rapidly filled to overflowing, and when, at last, one general rain 
came over the whole Des Moines River valley, these ponds, which were 
already filled to their utmost capacity, overflowed, flooding the river flat 
for miles in width, forest trees were drowned, bridges destroyed, crops 
inundated, heavy deposits of silt formed and everything growing was 
made profitless, except the late crop of hay, which practically formed 
after the flood. Let us still consider that we are in a balloon, watching 
the whole preceding. Had we been able, with our fingers, to trace some 
channels to conduct water from these depressions to the main river chan- 
nel, enabling them to carry, from the water-shed, excess waters and thus 
prevent the great accumulation which finally overloaded the whole river 
