The Provo next follows a narrow rock bound valley for 7 miles, being skirted by bottom lands that admit of some farming. It then enters Provo Valley, an opening about as large as the last, and favored by a warm climate that permits the growth of breadstuffs. Thence to Utah Valley it follows a deep, close cañon.
The volume of the Provo is sufficient to water about 100 square miles. If it be permitted to serve 28 miles in Kamas Prairie and 40 miles in Provo Valley and its adjuncts, there will remain for Utah Valley the quota for 32 miles. The minor streams of the valley, American Fork, Spanish Fork, Hobble Creek, Payson Creek, etc., will irrigate 120 miles, making a total of 152 square miles supplied with water. The total land of the valley which might be irrigated if the water were sufficient amounts to no less than 225 miles.
Thus it appears that if all available lands on the upper Provo are reclaimed, one-third of Utah Valley must go unwatered, while if none of them are irrigated, nearly the whole of the valley will be supplied. A middle course would appear most wise, and will undoubtedly be followed. A gradual extension of the canals, as the demands and means of the communities dictate and permit, will bring lands successively into use in the order of their value and convenience, and when the limit is reached and title has been acquired to all the water, the most available lands in each of the three valleys traversed by the Provo will have been reclaimed. The residents of Kamas Prairie will probably have increased their meadows so as to furnish winter hay for herds sufficient to stock the summer pastures of the vicinity; Provo Valley, having a less favorable climate than Utah Valley, will have irrigated only its choicest soils; and the major part of the river will belong to Utah Valley. The apportionment may be roughly estimated as—Kamas Prairie, 10 miles; Provo Valley and Waldsburg, 20 miles, and Utah Valley, 70 miles.
Below Utah Lake there is little inequality of volume dependent on season. The lake is a natural reservoir 127 square miles in extent, and so far equalizes the outflow through the Jordan that the volume of that stream is less affected by the mean level of the lake than by the influence of northerly and southerly winds. With suitable head works its volume can be completely controlled, and, if desirable, the entire discharge of the lake can be concentrated in the season of irrigation.
The highest stage of the lake is in July, and the lowest in March or April; and the natural volume of its outlet has of course a corresponding change. In July I found that volume to be 1,275 feet per second, and I am informed by residents that the stream carried more than one-half as much water in its low stage; 1,000 feet is perhaps not far from the mean volume. When all possible use is made of Provo River and other tributaries the annual inflow of the lake will be diminished by about one-eighth, and the outflow by a greater fraction, which we will assume to be one-quarter. (This postulates that the evaporation is at the rate of 90 inches per year for the whole lake surface.) The remaining perennial outflow of 750 feet per second, if concentrated into four months, would irrigate for that period 350 square miles. It will be practicable to include under canals from the Jordan only about 160 square miles of farming land, and I think it safe to assume that the supply of water will be greatly in excess of the demand.
At the present time the Jordan is little used, the chief irrigation of Salt Lake Valley being performed by the large creeks that flow from the mountains at the east. It will not be long, however, before large canals are constructed to carry the Jordan water to all parts of the valley that lie below the level of Utah Lake. They will include 120 square miles of farming land.
The mountain streams, being no longer needed in the lower parts of the valley, will be carried to higher land and made to serve the benches at the base of the mountains. By these means the total agricultural area of the valley will be increased to 192 square miles. Eventually, the western canal will be carried about the north end of the Oquirrh range and made to irrigate the northern third of Tooele Valley. It will pass above the farming lands of E. T. City and Grantsville, and enable the streams which irrigate the latter town to be used upon the higher slopes. The service of the Jordan will amount to no less than 40 miles and the agricultural area of the valley will be increased to about 45 square miles.
Including Tooele Valley and Kamas Prairie with the drainage basin of the Jordan, its agricultural resources sum up as follows:
| Tracts. | Square miles— | ||
|---|---|---|---|
| Cultivated in 1877. | Cultivable. | ||
| Kamas Prairie | 4.0 | 10.0 | |
| Hailstone Ranche and vicinity | 2.0 | 2.0 | |
| Provo Valley | 6.0 | 16.0 | |
| Waldsburg | 2.0 | 2.0 | |
| Utah Valley | 59.0 | 190.0 | |
| Goshen | Salt Creek | 14.0 | 16.0 |
| Mona | |||
| Nephi | |||
| Salt Lake Valley (including Bountiful and Centerville) | 89.8 | 192.0 | |
| Tooele Valley | 5.4 | 45.0 | |
| Total | 182.2 | 473.0 | |
The drainage district has an area of 4,010 miles; 4¹⁄₂ per cent. are cultivated, and 11³⁄₄ per cent. may be cultivated.