DEPENDENCE OF IRRIGATION UPON FORESTRY.
GUY E. MITCHELL,
* * * In the western half of the United States the destruction of the forests has an intimate bearing upon the capacity of the State to sustain population, for population results from irrigation, irrigation depends upon water supplies, and the water supply is furnished from the melting snows caught and held by the forest clothing the great mountain chains of the Sierras and the Rockies.
What is needed to-day is vastly more strength to the arm of American forestry for the vigorous prosecution of its carefully outlined plan to save what we now possess. The two greatest problems before this country to-day are forestry and irrigation, For can anything be of greater import than the creation of an empire within our midst which will support a population as great as that of the entire country to-day?
F. H. NEWELL,
The Government, through the operation of the reclamation act of June 17, 1902, is building large irrigation works throughout the West. The fund for that purpose now amounts to about 25 million dollars. These works, national in character, are being built as rapidly as possible. The protection of these works, their future use, their stability through all time, are very largely dependent upon the proper treatment of the forests which lie upon the mountains above the reservoirs. In fact there is hardly a project now under consideration whose future success is not closely joined with the questions of the best use and preservation of the forests, and, to a less degree, of the grazing land immediately adjacent. These works are being built to last for all time, and if they are to be preserved in their best condition it can only be after we have solved this question of the protection and best use of the forests.
* * * Take Arizona, for instance. Here the Reclamation Service is building a storage dam at Roosevelt costing probably 3 million dollars. When built it will enable the creation of homes for many thousands of people and render productive a large area now desert. For the protection of the Arizona reservoir a forest reserve must be had above the reservoir, in order to prevent, as far as possible, the washing of soil, which follows upon the destruction of tree growth. In Colorado is the Gunnison tunnel 30,000 feet in length, to take water from the Gunnison River into the Uncompahgre Valleya broad, fertile, but arid plain. The headwaters of that river must be protected in part by the forests as well as by reservoirs. In Idaho the same is true.
This matter of the development of the West is not a State question, but is interstate. We must build reservoirs in Wyoming; we must conserve forests in Wyoming to benefit the arid plains of Idaho. In western Kansas there is the greatest interest in irrigation, and although there are no forests the rivers that come into Kansas, as the Arkansas, depend partly for the continuity of their flow on the proper treatment of the woodlands on the mountains in the central part of Colorado. In Montana and Nebraska are similar conditions. In Nevada is under construction one of the largest irrigation works in the world. The integrity of that great system, which will cost at least 3 million, and possibly 5 million dollars when it is completed, will depend largely on the conservation of the forest growth in the State of California.
J. B. LIPPINCOTT,
* * * A striking example of the output of a barren, treeless drainage basin is shown in the case of Queen Creek, Arizona. This stream discharges only in violent freshets, recurring usually as great flood waves, subsiding almost as rapidly as they arise. During the larger part of the year the channel is almost dry. The area of the drainage basin is 143 square miles.
In contrast with Queen Creek is Cedar Creek, in Washington. The drainage area is the same as that of Queen Creek. It is heavily timbered, and in addition the ground is covered with a heavy growth of ferns and moss. The total annual rainfall in the Cedar Creek basin in 1896 was about eight times that in the Queen Creek basin, yet the maximum flood discharge per second is only 3,600 cubic feet for the former, while the maximum for the latter was 9,000 cubic feet per second. The mean discharge for Queen Creek was 15 cubic feet per second, and for Cedar Creek 1,089 cubic feet per second. These two streams represent extreme types. The radical difference in their character is believed to be largely due to the difference in forest cover.
ARTHUR P. DAVIS,
* * * Although the tendency of modern construction is to the use of the more permanent materials, less subject than wood to destruction and decay, the requirements of irrigation works are very great for piling and subaqueous structures to which wood is well adapted, and for buildings and the large class of temporary structures required. No satisfactory substitute has yet been found for timber in tunnels, and every structure of concrete requires wooden frames. It is not too much to say that the feasibility of some important irrigation works depends upon the proximity of ample timber supplies.
The development of irrigation will in the future lead to the rapid opening and development of timbered areas which are now merely in their natural state. This fact emphasizes the necessity of placing the forests at once under the rigid scientific supervision of trained Government experts. If left to the manipulation of selfish interests as in the past, the result will be lavish and wasteful use and probably destruction of the forest.
Last Updated: 01-Apr-2008