FOREST COVES IN PROTECTING RESERVOIRS 15 
An examination of the basin of a stream might show that prac- 
tically all of the erosion, including the heaviest portion of the solid 
burden which enters the reservoir, consisting of the large sand, the 
small sand, and the coarser silt, is derived from approximately 
6.000 acres of steep land now being cultivated annually to tilled crops. 
and that there are in addition 4.000 acres of land the erosion from 
which is less serious, but on which erosion should be checked within 
a period of not more than five years. 
It is ascertained that the 6.000 acres can be acquired at an average 
price of not more than 815 an acre and can be planted at a cost of 
not more than sS an acre. These lands, being hilly, are of low 
productivity in farm crops but are of good productivity in timber. 
In addition to expending 812.50 an acre, which represents the value 
of the land when planted for timber production, it would be finan- 
cially advantageous to expend a sum not exceeding the 8353.650 
mentioned above. 
An examination of the 4.000 acres on which erosion is less active 
might show that natural seeding from near-by old trees could be 
expected to restock this land in forest growth within a period of 
five years, and that consequently it would be unnecessary to resort 
-to the expense of planting, so that the purchase price of the land. 
allowing for natural restocking, would be within the investment 
value of the property in growing timber. 
SETTLING BASINS 
In addition to planting, it is possible and even desirable in some 
places to employ settling basins, within which much of the heaviest 
material at least may be left by natural elutriation. For this pur- 
pose, rough alluvial lands should be selected which have been injured 
by gullying during floods or upon which sand or gravel bars have 
been deposited. By means of low and inexpensive dams such lands 
can be flooded. The deposit from the slow-moving water will, in 
a few years — the period varying with the amount of sedimentation 
height of dam. and rapidity of current — reach the top of the dam. 
except in the stream channel. The dam will then have performed 
its function. Settling basins are therefore a temporary expedient. 
They may be employed with a view to preventing loss in storage 
capacity of the reservoir while a planting program is being worked 
out and executed. (PL 11.) 
Lands built up by means of a settling basin may be made valuable 
for farming purposes by the removal of a portion of the dam at 
one point so as to permit the stream again to seek its normal or 
former channel bed. Soils so deposited are free from stone and 
gravel and enriched by the sedimentation from the slack water. De- 
posits of this kind frequently fringe the entire upper margins of 
large reservoirs. Such, for example, are the deposits in the reservoir 
at the Muscle Shoals 15 development, which in places would now be 
suitable for agricultural use if the water table were lowered only a 
few feet. Artificially formed alluvials of this kind after the removal 
of a portion of the dam are level and would generally be above the 
15 See footnote 5, reference to p. 111. 
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