« PreviousContinue »
of the supply invariably rises. A study of the water supply of this valley leaves little room for apprehension. The water-bearing stratum, composed of sand and gravel, is in effect a large storage reservoir. Considering the fact that the river, which naturally flows in the lowest part of the valley, acts as a drain to carry off surplus ground water, it is evident that this reservoir must be full to overflowing whenever there is running water in the river. No one would expect to use water from an ordinary storage reservoir without lowering the water surface, and the mere fact that the ground-water elevation drops during the irrigation season is no cause for alarm. The real test is whether or not the water supply of the valley is sufficient to fill the subterranean reservoir each year during the nonirrigating season. It not only does this, but each year more than a million acre feet of water flows out of this valley on its way to the ocean.
PAWNEE AND WALNUT VALLEYS. There are approximately 2,700 acres irrigated in the valleys of the Pawnee river and Walnut creek. The larger part of this, 2,300 acres, is along the Pawnee.
While most of the irrigation in this district is in the Pawnee valley, the two are much alike as regards physical features, rainfall, and water supply. Both streams have deep channels eroded down through heavy alluvial soil, and both flow through nearly level valleys, which vary in width from one to three or four miles. The banks of these streams have been built up by overflowing flood water until in many places the immediate bank is higher than the adjacent land. This building up has been so great in some instances that water released at the river bank will flow for a distance of nearly two miles in a direction at right angles to the stream. On a most every quarter section of land through which the stream passes, a point can be found along the bank from which water will flow over practically the entire quarter.
The normal flow of these streams is not indicative of the amount of water they will supply for irrigation. The dry-weather flow of these streams is two or three cubic feet per second, and it is seldom more than ten second feet unless flood water is present. Any extensive irrigation from these streams would be impossible without orage, but the deep channels offer most favorable conditions for the building of dams and the storage of water. A number of such have been built, and their use for storing water and developing a water supply for the valley has been proven highly successful. In a channel which has a slope, as the Pawnee has, of only from one to two feet per mile the building of a dam ten or twelve feet high creates a reservoir several miles long and stores a large vo'ume of water, but the invisible storage due to these reservoirs appears to be even greater than the visible storage. Soon after a dam is built, freshets coming down the channel fill the reservoir full to overflowing and raise the surface of the water in the channel by an amount equal to the height of the dam. This water, some of which gradually seeps out under the adjacent land, gradually raises the water table until within a few years the ground-water e'evation in the surrounding valley is as high as the top of the dam. Water for irrigation is pumped from these reservoirs. During the first few days of pumping the surface of the water in the reservoir drops several feet, but a point is soon reached where the inflow of the surrounding ground water so nearly equals the amount pumped out that even a continued period of pumping has but little effect in further lowering the water in the channel.
The increasing of the amount of water available for pumping from reservoirs has not been the only beneficial result of the raising of the ground-water elevation. In many places the water table has been raised close enough to the surface to subirrigate growing crops. Several striking examples of this are afforded by alfalfa fields, which in former years often suffered from drought. but which since the raising of the water table are productive throughout the summer, and regularly yield almost as much as surface irrigated fields.
Some of the dams on the Pawnee have been in use for more than ten years. Their value as a means of storing and conserving the surface run-off of these drainages has been so well demonstrated that it is evident, if dams were built at distances of four or five miles apart throughout the courses of these streams, enough water could be stored to irrigate all of the adjacent bottom land.
The typical irrigation plant in the Pawnee valley consists of a dam in the river channel and a pumping plant on the adjacent bank to pump water from the reservoir thus formed. There are a few irrigation plants throughout the valley pumping from wells, but the underground strata are not favorable for extensive irrigation from that source.
Crops grown here are for the most part general farm crops, such as alfalfa, corn, kafir, etc. There is a small acreage of sugar beets raised each year and shipped to the beet sugar factory at Garden City.
Irrigation in Scott county is noteworthy in that there is a well-developed irrigation agriculture remote from any river valley. About 5,000 acres are irrigated with a water supply obtained wholly from wells.
An abundance of water can generally be found almost anywhere in the central or southwestern part of the county at depths ranging from twenty to sixty feet below the surface. In some places this water-bearing formation is of such a nature that single wells have produced a yield as great as 2,000 gallons per minute. Most wells will yield at least enough to supply a quarter section of land.
Pumping plants, for the most part, consist of a single well (usually about twenty-four inches in diameter), a type of centrifugal pump comme
monly known as a deep-well turbine pump, and either an internal-combustion engine or an electric motor for power. Many of the pumping plants are using an engine for power, but a transmission line extends from Garden City to this district and electric energy is available for all who wish to use it. A notable project here is on the Lough ranch, where Mr. Lough has built a central power station and is operating a number of pumping plants on various parts of his ranch with the electricity generated at this central station. A large oil engine, burning lowgrade fuel oil, is used for power.
The principal crop in this district is alfalfa. Both the soil and the climate are well adapted to this crop. Some of the finest alfalfa fields in the state are here, and remarkable yields have been obtained from them. Yields of from five to seven tons per acre are common, and some as high as nine tons per