IMMEDIATE RELEASE Glynn Harvey, News Editor
ASPHALT SEEN HOPE FOR HALTING WATER WASTE IN WESTERN STATES
More than 134,000 miles of canals and laterals in the United States carry 95,441,491 acre-feet of precious water annually from storage basins to point of irrigation in our 17 western states.
This serves to irrigate 24,270,566 acres of range and farmland---an area larger than the entire state of Indiana.
But seepage losses of water in transit through these canals cost these semi-arid states more than 18 million acre-feet each year. This is three times the volume of water used each year for all irrigation purposes in the state of Utah where, in 1847, modern irrigation was begun by the Mormons who diverted
the waters of City Creek in Salt Lake City.
This tabulation of annual water waste, presented by George P. South of the Bureau of Reclamation at Salt Lake City, highlighted the First Western Conference on Asphalt in Hydraulics, held at the University of Utah under the co-sponsorship of the University of Utah, The Asphalt Institute and the Utah Water Users Association. The proceedings of that trail-blazing conference have just been published by the University of Utah Press.
The discussion by a panel of 19 engineers covered a wide range of asphalt uses from reservoir lining to asphalt groins for beach stabilization.
Primary attention, however, was focused on the problem of low-cost canal lining to conserve the vast quantities of sorely needed water now being lost through seepage.
Keynoting the conference, B. A. Vallerga, Managing Engineer for The Asphalt Institute at San Francisco, declared:
"In the field of water conservation, minimizing losses due to seepage and leakage is a consideration of highest priority. Ideally, all water storage and carrier systems, such as reservoirs, canals and irrigation ditches should be watertight. Besides decreasing water losses, such a dition would actually increase the efficiency of water con-veyance and would preclude the waterlogging of adjacent property with its undesirable and sometimes costly effects.
"To accomplish this objective, the search for durable lining materials resistant to the passage of water is con-tinuing through sound engineering programs of research and development by many interested groups. Because of the enormous areas of linings needed, however, the factor of economy is one of paramount importance, challenging the ingenuity and resources of the engineer to the utmost ..• "
Principal work in this field has been done by the Bureau of Reclamation which, in 1946, expanded its research facilities to explore the use of asphalt
for low-cost canal lining. Ten years later the Bureau has 84 asphaltic structures in 15 states, 15 of these located in California and 14 in Wyoming.
Reviewing asphalt construction in the West, L. M. Ellsperman of the Bureau of Reclamation at Denver told the conferees the Bureau's first installation of asphalt membrane lining was made on the Klamath Project, in California, in 1947. Since that date, said Ellsperman, more than seven million square yards of this type of lining have been placed by the Bureau. Largest single installation was the two million square yards placed on the Columbia River Project in
Washington.
An asphalt membrane is a tough, pliable lining of from 1/4 to 3/8 inches built up by spraying high softening point asphalt at high temperature
-more-directly on the prepared subgrade. This membrane then is covered with layers of earth or gravel to hold it in place and protect it against weathering and livestock damage.
Average cost of this type of lining, said Ellsperman, was 80 cents per square yard with a maximum cost of $1.50 per square yard where special problems are encountered.
11In addition to being low in cost,11 said Ellsperman, "this type of lining_ can-be satisfactorily installed under nearly any subgrade condition, and in cold and wet weather such as is frequently encountered in northern latitudes
during the non-irrigation season. Late fall and winter is
frequently the most convenient time for installing lining in operating systems, but freezing temperatures and wet subgrade conditions are prohibitive for more conventional types of lining.
"Asphalt membrane may be satisfactorily placed over frozen subgrades and sometimes, though it is not recommended,
over light coverings of snow. Factors contributing to the low
cost obtained on many membrane constructions are that membrane linings may be constructed with equipment ordinarily in
possession of the average highway contractor and may be placed during an otherwise slack season.11
Ellsperman said originally it was thought that a membrane thickness of about 3/16 of an inch, the equivalent of about one gallon per square yard,
would be adequate. Experience has proven, however, that thickness of 1/4 to
5/16 of an inch, or about 1.5 gallons per square yard, gives the membrane longer "life" and greater protection against damage.
"Buried asphalt membrane," said Ellsperman, 11has proved to be an efficient and durable, yet low-cost, means of seepage
control under many difficult conditions of use. Maximum
benefit is obtained from this type of construction by the use of an adequate quantity of the proper type of asphalt care-fully applied to avoid holidays and to secure uniform thickness and by the use and maintenance of adequate protective cover. The type and thickness of cover material required to with-stand high water velocities constitute the major problem of
buried membrane design. Asphalt and emulsion macadams are
now being considered as alternatives to very thick earth or a heavy gravel blanket. 11
Another application of asphalt in canal lining, said Ellsperman, has been the development of prefabricated linings. Manufactured in panels or rolls, these linings can be constructed easily and quickly with unskilled farm or
ranch labor. These are particularly useful in lining small canals and laterals. In recent years an exposed type prefabricated lining, manufactured in sheets three feet wide and ranging in length from eight to fourteen feet, has been introduced. These half-inch thick panels of a~phalt-saturated felts with filler cores handle easily, conform nicely to the contour of the soil at
temperatures as low as 20 degrees Fahrenheit, and promise to find increasingly wide acceptance.
According to Ellsperman, there is an increasing interest in asphaltic concrete lining of which more than 300,000 square yards have been placed by the Bureau of Reclamation since 1946.
11Probably the most important immediate factor
affect-ing the future development and use of asphaltic concrete for both canal liniogs and dam facings is the design and development of equipment for placing such mixtures," said Ellsperman. ''As yet, no completely satisfactory placing equipment has been built, though some have closely
approached the goal.
"Existing machines for lining canals are usually so l0ng as to be awkward to operate around curves~ ~This necessitates hand finishing in curved areas, or lt creates
thin lining areas which may require future maintenance ••• "
The primary function of the asphalt lining was defined clearly by Jewell R. Benson, credited with much of the early experimental work in this field while he was associated with the Bureau of Reclamation. Benson is now a consulting engineer in Denver.
"When competing types of construction are available," said Benson in his opening remarks, "the final selection of the type to be used in any particular installation will probably be based either upon the ability of a certain type
-more-to perform outstandingly in that use, without particular regard to the cost, or to perform equally or acceptably at appreciably lower initial cost.
"The uses of asphaltic ,naterials in hydraulics may fall into either of these classifications and sometimes with outstanding performance while still retaining low
cost, but in general, the conditions most highly stressed are good performance at low cost.,,"
Benson said early laboratory studies were made to find a solution to
the weed control problem. Under certain c-0nditions, where a soil steri-1-ant
is not used on the subgrade, asphalt linings are plagued by tule and cat-tail weeds which find ideal germinating conditions beneath these asphalt covers and, growing, pierce the lining. Benson said it was learned that a medium hard cutback asphalt, compacted to a reasonably high density, could withstand weed pressures.
An asphalt of similar consistency, he added, also proved highly
resistant to mud-curl, another lining hazard. Mud-curl occurs where there is
a daily cycle of wetting and drying with deposits of mud. As the mud dries,
it has a tendency to curl, bringing with it small quantities of asphalt surface. Benson said other tests developed that certain aggregates used in
asphaltic concrete mixes were hydrophilic (water-loving) and tended to attract
and retain water. This, he said, rendered the lining less impermeable,
destroying or reducing the efficiency of the waterproof liner.
Speakers included Baron van Asbeck of the Shell Petroleum Co, Ltd., London, who delivered a paper describing the developments in the use of asphalt for hydraulic structures in Europe, mainly seawall and jetty grouting.
