99 BULLETIN 1358, U. S. DEPARTMENT OF AGRICULTURE 
SO that concentration, overgrazing, and erosion in any one sector — 
will be reduced to a minimum and silting thereby retarded. It 
is also worth while to consider the possibilities of satisfactory loca- 
tion below the reservoir of troughs, corrals, and other handling — 
facilities. Dirt for the embankment should be near at hand. [ 
Promising sites should be examined closely to ascertain the pos- 
sibility of locating the spillway near the upper end of the body of 
water rather than the lower, which has been the practice in most’ 
regions. This can often be done without extra cost if planned for > 
before construction work begins, although fewer sites meeting this 
requirement will be found. cy 
Tissured ledges or rock outcrops, particularly in limestone lo- © 
calities, should be avoided, unless to do so means sacrificing very — 
desirable features which can not be duplicated elsewhere. An earth hd 
embankment should never abut against an overhanging ledge, since 
the settling of the dirt mass will open crevices “underneath the | 
rock roof. | 
Ordinarily sites immediately above steep slopes or break of any @ 
kind should be avoided because of the greater risk from rapid seep- 
age; however, occasional small storage basins have proved water- — 
ticht even when placed within 100 feet of the rims of deep canyons. 
“A suitable location may otten be found on a flat or mesa, espe-— 
cially if the reservoir is to be filled from a ditch tapping a near-by | 
stream. Shallow natural depressions which hold water for only ~ 
short periods each year may often be cheaply developed into worth- ~ 
while watering places through the construction of diversion ditches, — 
and, if needed, a small retaining dam. From the erosion-control | 
standpoint, the development of watering places away from stream ~ 
channels is desirable. 
SIZE OF RESERVOIR 
The size of the reservoir needed will depend on the water require- — 
ments of the livestock to be watered, together with the period of de-— 
pendence, frequency of filling, loss from seepage and evaporation, 
and danger of reduction in capacity from siltmg. Additional al- — 
lowances should then be made because all reservoirs will not fill _ 
every year. le 
The period of use is extremely important. If the watering place ~ 
is to be used only temporarily to reduce grazing about a more per- ~ 
manent development, a small reservoir which will fill from heavy © 
rains and hold sufficient water to meet the needs of the livestock — 
for a few weeks or months thereafter will suffice. Where reservoirs © 
are expected to furnish water throughout the year, however, and © 
especially during protracted droughts such as occur in the Southwest | 
periodically, liberal size allowance must be made. | 
All available information should be obtained on the frequency of | 
filing to be expected. If reservoirs are filled from streams which | 
flow for several months or from washes where frequent flows occur 
year after year, a much smaller basin can be made to serve than 
in cases where the feeder drainages flow only for short periods dur- 
ing the spring thaws or summer rains. 
