The Eternal Battle

The Eternal Battle of Man

STREAMS in Arizona dump millions of tons of soil into the Colorado River each year. During floor stages erosion is so great that some of the main streams carry as much as 60 per cent silt. The cutting power is so great that earth banks disappear suddenly.

To protect highways against such power, revertments, levees, reflectors and jetties are used. Experience has taught us that deflectors made of rigid construction have a tendency to fight the water and its power, which results in destruction below or at the end of the deflectors. It is therefore reason-able to assume that the deflectors should be made of material that will allow the water to pass but check the current, thereby reducing the velocity and its cutting power.

The swifter a stream is, the heavier fragments it will carry in suspension. If the velocity is checked to one-half the previous velocity i's carrying power is reduced 64 times. If the velocity is checked to one-third the previous velocity, its carrying power is reduced 729 times. A current of 20 miles an hour will carry rocks weighing 100 tons; ten miles an hour or 15 feet per second, one and a half tons; five feet per sec-ond, about three and a half pounds.

The new method for checking velocity, building up new ground, deflecting the course of flood from bridge approaches, straightening channels, re-ducing destructive cutting power, is as follows: Railroad rails driven solidly in the ground from five to eight feet centers, a line of woven wire fence or welded wire fence, placed on the line of rails. The size of the openings in the fence, the gauge of the wire, floor mats, size of rail used, is governed by the carrying power of the stream.

Arizona is using in the major streams 62½ pound rails, driven with a pile driver eight to ten feet into the ground, center rails six feet, the line is straight at an angle of 45 degrees with the stream flow above. The line is long enough to turn away the swift flow entirely from the bank. On the rail is placed 58 inches 12½ gage woven wire fence, V mesh type, single, doubled or tripled, three to four-inch openings, securely tied to rails. One roll of wire is matted on the upstream floor and tied to the fence to prevent scour.

The cost of this operation includes rails at $15.00 per ton, 40c per foot and fence 20c (3 ply); labor 20c; miscellaneous cost, 10c, or a total of 90c per lineal foot installed. Where smaller

and Water Arizona Highway Department Develops Unique and Economical Deflectors

pile driver is used (600 pound hammer) 30 rails average for one day, 8 to 10 feet in the ground and 180 feet of fence complete.

Floods this year have occurred oftener and more severely than in the past five years. The velocity checks described in this article were used only after the damage to the banks near the highway was done. The checks were used to prevent further damage. In these places the checks have turned the stream to its original channels and built up ground in front and back of the line of fence. In the future this system will be used to prevent cutting in places that are subject to channel change and where the banks are liable to cutting.

Since the Highway Department's experiments with this type of deflector the Soil Erosion service and the South-ern Pacific Railroad Company, whose problems are similar to the Highway Department, are using this device to change channels and their currents, build up new ground, straighten streams and plugging gaps in newly made arroyas. They are more than satisfied with the results and we predict that in a very short time this system will be iversally used.