Mr. Le Conte. 
330 DISCUSSION : FORESTS, RESERVOIRS, AND STREAM FLOW 
passed through 40 miles of continuous and unbroken wheat field. In 
places the wheat stood 42 in. high, was well headed, and, when harvested, 
frequently averaged 60 bushels to the acre. The surveying party 
began work early every morning without exception, and every member, 
the chainmen especially, was drenched with the heavy dew on the 
wheat, and never got dried out until noon each day. This continued 
for five days while passing through this mammoth wheat field. Of 
course, the popular phrase “dewfall” is a misnomer. The phenomenon 
is purely one of condensation; nevertheless, it is a very important and 
material element in the daily precipitation in the open, and should 
not be overlooked. In the forests, of course, this is nil. 
Another most interesting feature about these plains is the effect 
of cultivation on the surface run-off. Experience everywhere shows 
that plowing the surface soil reduces the surface run-off enormously. 
The reason for this is easily understood when the physical facts 
are known. In the natural state the surface soil is generally sun- 
baked and hard. When the rains come, this surface crust sheds 
water like the roof of a house. On the contrary, when this land is 
plowed up into deep furrows, after the first rains have softened the 
ground, all the rainfall thereafter sinks in, and the run-off is practi- 
cally nothing. More than that, the top soil, being broken up and porous, 
stops subsequent surface evaporation enormously, and holds the ground- 
waters for the subsequent useful purposes of agriculture. 
Of course, later in the season, when very heavy and prolonged 
rains come, the surface wash from the plowed lands is more heavily - 
charged with sediment than it would have been before the lands were 
plowed. It should be remembered, however, that this run-off lasts for 
a much shorter time, and, therefore, it is an open question whether, 
considering the entire year, cultivation materially increases the total 
solids transported to the streams. The effect of cultivation, therefore, 
is to store the rain-waters in the soil, reduce surface evaporation, and 
enlarge and equalize the flow of ground-waters to the streams. These 
functions are certainly in keeping with the requirements of conserva- 
tion, and tend to increase the percentage of annual run-off to rainfall. 
At all events, observations on lakes and artificial reservoirs certainly 
fail to show any noticeable increase in silting up due to cultivation 
of the soil. 
The author’s remarks about the relative efficiency of storage reser- 
voirs in controlling the flood-water flow of rivers are exceedingly 
timely and strictly to the point. If these reservoirs are to be used 
for power or irrigation purposes, all efforts at flood control must be 
abandoned. The all-powerful interests of water-power and irrigation 
are diametrically opposed to storage capacity for the accommodation 
of great storm-waters, as these generally come at the end of the wet 
season. These two interests can never be reconciled, but will always 
