It is probable that a portion of the Virgin River can be used to advantage below the Beaver Dam Mountains in Nevada, and that a sufficient amount to irrigate 25 square miles can be used to good advantage in Utah.
The time when the volume of available water furnished by any stream bears the least ratio to the demands of the growing crops is the most critical period in the cultivation of the soil where artificial irrigation is a necessity. This time, depending as it does upon the crops cultivated, the character of the soil, and the source of the water supply, whether from springs or from melting snows, differs in different localities. In the valley of the Virgin it occurs in June.
At this time the river, though not at flood height, which occurs in April, carries a large volume of water, and, by reason of the source of this supply being in the rapidly melting snows of the Colob Plateau, is decreasing but slowly, and thus the amount available at this critical period bears a greater ratio to the flood of the stream than is usual in Utah. But little information has been obtained concerning the amount of water necessary to irrigate an acre. It is thought, however, to be much greater than in any other portion of Utah.
KANAB CREEK.
Kanab Creek rises in springs bursting from underneath the cliffs forming the southern boundary of the Pauns-a-gunt Plateau, and flows southward until it joins the Colorado River in Arizona. Small areas of arable land are found along its course after it has descended to an altitude of 7,500 feet, and thence until it passes beyond the boundaries of Utah. The largest area in one body is in Kanab Valley, at the foot of the Vermilion Cliffs. It is greatly in excess of the water supply, is at an altitude of about 5,000 feet, has a fertile soil, and requires but comparatively a small amount of irrigation. The amount actually under cultivation in 1877 is placed by the best information attainable at 700 acres. The critical period in the cultivation of this area occurs in June. At that time the stream is falling rapidly, and crops have sometimes been seriously damaged. Estimates of the volume of water in the stream, made at different seasons and in different years, give 15 cubic feet per second as the flow in June. Some desultory attempts have been made to increase the supply by ponding, the cañon through the Vermilion Cliffs above the arable lands affording many opportunities. When this improvement is made on some well considered and well executed plan, and the waterways flumed through some bad sandy ground that now absorbs much water, the amount available at the critical period can be at least doubled.
Some years ago a settlement was established at the foot of the Pink Cliffs, on the headwaters of the Kanab, but the town site was eventually abandoned because of the deep snows of winter and the frosts of summer.
THE PARIA RIVER.
The Paria River rises under the eastern escarpment of the Pauns-a-gunt Plateau, at about the same altitude as Kanab Creek, and flows in a southwesterly course for 100 miles, joining the Colorado in Arizona. Through the greater part of its course the river flows in a deep cañon, but near its head, and at an altitude of 6,000 feet, the cañon expands into a valley. Lower in its course, and at an altitude of 4,500 feet, the cañon again widens into a smaller valley. These are the only areas of arable lands within its drainage basin in Utah. The larger contains 15 and the smaller 10 square miles. In August, 1874, this stream flowed 30 cubic feet per second in the upper valley. The flow in the lower would be one-third greater. High water occurs in April or early in May. At this time the volume is three times greater than in August. Settlements have been made in both valleys, and quite a large area is under cultivation. The soil is excellent.
The critical period in irrigation is the latter part of June or early in July. At this time the stream probably carries 40 feet per second. The land in the lower valley is much subject to flooding from heavy showers that, falling on the table lands and mesas in the upper portion of the drainage basin, pour a torrent often beyond the capacity of the channel to convey through the lower valley. So great was the damage done by these floods in sweeping away dams, breaking through ditches, and inundating the growing crops at the site first selected for settlement, that it was abandoned after three years’ occupation, and other parts, where these sudden rushes could be controlled, selected. Considerable difficulty has been experienced in the lower valley from the vast amount of argillaceous sediment deposited on it. So great during the floods is this deposit from the water used in irrigation that the ground becomes completely coated with an impervious layer, and growing crops, especially of small grains, suffer from the inability of the soil to absorb the water conducted on it. The irrigating capacity of this stream during the critical period could be greatly increased by the construction of reservoirs in which to store the great surplus of water that flows earlier in the season. The cañons above the valleys offer very favorable opportunities for building the necessary dams and embankments.