RANGE WATERING PLACES IN THE SOUTHWEST oF 
upkeep item has already amounted to at least twice the original 
construction cost. : 
In repairing earthen dams, it is often very difficult to secure a 
water-tight bond between old and new work, especially where 
freshets have torn out an entire section. One such repair of a dam 
50 feet high was successfully made by a crescent-shaped “ plug,” 
which more than doubled the contact surfaces of old and new earth, 
‘although in general little advantage would seem to result from build- 
ing earth dams to bow upstream. In another case success 1n restor- 
ing a washed-out section was attained only after inserting a con- 
erete core 4 or 5 feet high lengthwise of the dam, extending across 
the gap and into the solid earth on either side. 
MASONRY AND CONCRETE DAMS 
There are many adequate storage basins in narrow canyons with 
exposed rock ledges (Pl. XVIII, fig. 2), where water development is 
‘desired for livestock. Such sites are more suitable for masonry or 
concrete than for earthen dams. Though the original cost is higher, 
floods are not so liable to damage such structures, and if they are 
‘properly constructed the cost of repairs is low. They are justified 
sin preference to earthen embankments, however, only where con- 
(struction material is close at hand, solid foundations at or near 
‘the surface, and silting a minor factor. Removal of silt from a 
«narrow rocky gorge is difficult. 
_ Dams of masonry or concrete sometimes bow upstream for greater 
resistance to the impounded water but ordinarily are built straight 
across the drainage. Special spillways may be made for such dams, 
but as a rule excess waters are allowed to overflow the entire length. 
|The unit cost of such dams is much higher than for earth and it is 
_advisable that the design and construction (6, pp. 13-14) (18) (27) 
be handled by men experienced in concrete and rock work, in order 
_to insure economy and serviceability. 
The cost of structures of this kind depends upon the distance 
‘supplies must be moved, availability of suitable building materials, 
vand prices of material and labor. The few cost averages available 
sare given in Table 8 (4). 
| 
TABLE 8.—Available cost averages 
Kind Num- | Average | Average | Average Dates 
ber length height cost built 
Feet Feet 
AUIETS OT Tay peprseeem nen Deciuea Siar te vine 8 icici 5 92 16 $2, 100 | 1912-1920 
TICE CL cme atm onan Gua wenn Venn Sue ioe 8 44 934 345 | 1913-1922 
GRAVEL OR SAND FILLED RESERVOIRS 
An unusual type of reservoir found in a few places in the South- 
west is located above a masonry or concrete dam and completely 
filled by fairly clean coarse sand, gravel, or cinders. The percentage 
of open pore space in clean, dry sands or gravels may range from 30 
to 50 (23). It will likely be somewhat less than 30 in actual flood- 
washed material, which, even under most favorable conditions, con- 
