THEORY OF HUMAN AGENCIES.
The only remaining theory of value is the one advocated by Professor Powell: that the phenomena are to be ascribed to the modification of the surface of the earth by the agency of man. The rise of the lake and the increase of streams have been observed since the settlement of the country by the white man, and the sage brush on the old storm line shows that they had not been carried to the same extent at any previous period in the century. They have coincided in time with the extension of the operations of civilization; and the settlers attach this idea to the facts in detail as well as in general. They have frequently told me that wherever and whenever a settlement was established, there followed in a few years an increase of the water supply, and these statements have been supported by such enumerations of details that they seem worthy of consideration. If they are well founded, the secret of the change will surely be found among the modifications incident to the operations of the settler.
Similar testimony was gathered by Prof. Cyrus Thomas in 1869 in regard to the increase of water supply at the western edge of the plains, and the following conclusion appears in his report to Dr. Hayden (page 237 of the reprint of Dr. Hayden’s reports for 1867, 1868, and 1869):
All this, it seems to me, must lead to the conclusion that since the territory [Colorado] has begun to be settled, towns and cities built up, farms cultivated, mines opened, and roads made and travelled, there has been a gradual increase of moisture. Be the cause what it may, unless it is assumed that there is a cycle of years through which there is an increase, and that there will be a corresponding decrease, the fact must be admitted upon this accumulated testimony. I therefore give it as my firm conviction that this increase is of a permanent nature, and not periodical, and that it has commenced within eight years past, and that it is in some way connected with the settlement of the country, and that as the population increases the moisture will increase.
Notwithstanding the confidence of Professor Thomas’s conclusions, he appears to have reached them by a leap, for he makes no attempt to analyze the influence of civilized man on nature to which he appeals. Before we accept his results, it will be necessary to inquire in what way the white man has modified the conditions by which the water supply is controlled.
To facilitate this inquiry, an attempt will be made to give a new and more convenient form to our expression of the amount of change for which it is necessary to account in the basin of Great Salt Lake.
The inflow of the lake is derived chiefly from three rivers, and is susceptible of very exact determination. Thorough measurement has not yet been made, but there has been a single determination of each river and minor stream, and a rough estimate can be based on them. The Bear and the Weber were measured in October, 1877, and I am led by the analogy of other streams and by the characters of the river channels to judge that the mean volume of the Bear for the year was twice its volume at the date of measurement, and that of the Weber four times. The mean flow of the Jordan can be estimated with more confidence, for reasons which will appear in a following chapter. The “supply from other sources” mentioned in the table includes all the creeks that flow from the Wasatch Mountains, between Draper and Hampden, together with the Malade River, Blue Creek, the creeks of Skull and Tooele Valleys, and the line of springs that encircles the lake.
| Rivers, etc. | Measured volume in feet per second. | Estimated mean volume in feet per second. |
|---|---|---|
| Bear River, measured October 4, 1877, at Hampden Bridge | 2,600 | 5,200 |
| Weber River, measured October 11, near Ogden | 500 | 2,000 |
| Jordan River, measured July 8, near Draper | 1,275 | 1,000 |
| Supply from other sources | — | 1,800 |
| Total | — | 10,000 |
| Deduct the water used in irrigation | — | 600 |
| Remainder | — | 9,400 |
The result expresses the mean inflow to the lake in 1877, and is probably not more than 25 per cent. in error. The total inflow for the year would suffice to cover the lake to a depth of 60 inches. In the same year (or from October, 1876, to October, 1877) the lake fell 6¹⁄₂ inches, showing that the loss by evaporation was by so much greater than the gain by inflow. The total annual evaporation of inflowing water may therefore be placed provisionally at 66¹⁄₂ inches. If we add to this the rain and snow which fall on the lake, we deduce a total annual evaporation of about 80 inches of water; but for the present purpose it will be more convenient to consider the former figure.
The extent of the Salt Lake basin is about 28,500 square miles. The western portion, amounting to 12,500 miles, sends no water to the lake, yielding all its rainfall to evaporation within its own limits. The remaining 16,000 miles includes both plains and mountains, and its tribute is unequal. To supply 66¹⁄₂ inches annually to the whole area of the lake, 2,125 miles, it must yield a sheet of water with an average thickness of 8.83 inches. In former times, when the lake had an area of only 1,820 miles, the yield of the same area was 7.43 inches. The advance from 7.43 to 8.83, or the addition of 1 inch and 4 tenths to the mean outflow of the district, is the phenomenon to be accounted for.
All the water that is precipitated within the district as rain or snow returns eventually to the air, but different portions are returned in different ways. Of the snow, a portion is melted and a portion is evaporated without melting. Of the melted snow and the rain, a part is absorbed by vegetation and soil, and is afterward reabsorbed by the air; another part runs from the surface in rills, and a third part sinks into the underlying formations and afterward emerges in springs. The streams which arise from springs and rills are again divided. Part of the water is evaporated from the surfaces of the streams and of fresh water lakes interrupting their courses. Another part enters the adjacent porous soils, and either meets in them the air by which it is slowly absorbed, or else so saturates them as to produce marshes from which evaporation progresses rapidly at the surface. The remainder flows to Great Salt Lake, and is in time evaporated from its surface. The lesser portion of the precipitation enters the lake; the greater is intercepted on the way and turned back to the air. Whatever man has done to clear the way for the flowing water has diminished local evaporation and helped to fill the lake. Whatever he has done to increase local evaporation has tended to empty the lake.
The white man has modified the conditions of drainage, first, by the cultivation of the soil; second, by the raising of herds; and, third, by the cutting of trees.
1. By plowing the earth the farmer has rendered it more porous and absorbent, so that a smaller percentage of the passing shower runs off. He has destroyed the native vegetation, and replaced it by another that may or may not increase the local evaporation; but this is of little moment, because his operations have been conducted on gentle slopes which in their natural condition contributed very little to the streams. It is of greater import that he has diverted water already accumulated in streams, and for the purposes of irrigation has spread it broadly upon the land, whence it is absorbed by the air. In this way he has diminished the inflow of the lake.
Incidental to the work of irrigation has been what is known as the “opening out” of springs. Small springs are apt to produce bogs from which much water is evaporated, and it has been found that by running ditches through them the water can be gathered into streams instead. The streams of water thus rescued from local dissipation are consumed in irrigation during a few months of the year, but for the remainder go to swell the rivers, and the general tendency of the work is to increase the inflow of the lake. A similar and probably greater result has been achieved by the cutting of beaver dams. In its natural condition every stream not subject to violent floods was ponded from end to end by the beaver. Its water surface was greatly expanded, and its flood plains were converted into marshes. The irrigator has destroyed the dams and drained the marshes.
There are a few localities where drainage has been resorted to for the reclamation of wet hay lands, and that work has the same influence on the discharge to the lake.
2. The area affected by grazing is far greater than that affected by farming. Cattle, horses, and sheep have ranged through all the valleys and upon all the mountains. Over large areas they have destroyed the native grasses, and they have everywhere reduced them. Where once the water from rain was entangled in a mesh of vegetation and restrained from gathering into rills, there is now only an open growth of bushes that offer no obstruction. Where once the snows of autumn were spread on a non-conducting mat of hay, and wasted by evaporation until the sunshine came to melt them, they now fall upon naked earth and are melted at once by its warmth.
The treading of many feet at the boggy springs compacts the spongy mold and renders it impervious. The water is no longer able to percolate, and runs away in streams. The porous beds of brooklets are in the same way tramped and puddled by the feet of cattle, and much water that formerly sank by the way is now carried forward.
In all these ways the herds tend to increase the inflow of the lake, and there is perhaps no way in which they have lessened it.
3. The cutting of trees for lumber and fence material and fuel has further increased the streams. By the removal of foliage, that share of the rain and snow which was formerly caught by it and thence evaporated, is now permitted to reach the ground, and some part of it is contributed to the streams. Snow beds that were once shaded are now exposed to the sun, and their melting is so accelerated that a comparatively small proportion of their contents is wasted by the wind. Moreover, that which is melted is melted more rapidly, and a larger share of it is formed into rills.
On the whole, it appears that the white man causes a greater percentage of the precipitation in snow to be melted and a less percentage to be evaporated directly. This follows from the destruction of trees and of grass. By reducing the amount of vegetation he gives a freer flow to the water from rain and melting snow and carries a greater percentage of it to streams, while a smaller percentage reaches the air by evaporation from the soil. By the treading of his cattle he diminishes the leakage of the smaller water channels, and conserves the streams gathered there. By the same means and by the digging of drains he dries the marshes and thereby enlarges the streams. In all these ways he increases the outflow of the land and the inflow of the lake. He diminishes the inflow in a notable degree only by irrigation.
The direct influence of irrigation upon the inflow is susceptible of quantitative statement. Four hundred square miles of land in Utah and Idaho are fertilized by water that would otherwise flow to the lake, and they dissipate annually a layer of about 20 inches. To supply these 20 inches the drainage district of 16,000 miles yields an average layer of 0.5 inch, and this yield is in addition to the 1.4 inches required to maintain the increase of lake surface. The total augmentation of the annual water supply is therefore represented by a sheet 1.9 inches in depth covering the entire district.
The indirect influence of irrigation, and the influences exerted by the grazier and the woodman, cannot be estimated from any existing data, but of their tendencies there can be no question. To some extent they diminish local evaporation, and induce a larger share of the rainfall to gather in the streams; and to one who has contrasted the district in question with similar districts in their virgin condition, there seems no extravagance in ascribing to them the whole of the observed change.
In the valley of the Mississippi and on the Atlantic coast, it has been observed that the floods of rivers are higher than formerly, and that the low stages are lower, and the change has been ascribed by Ellet and others to the destruction of the native vegetation. The removal of forests and of prairie grasses is believed to facilitate the rapid discharge from the land of the water from rain and melted snow, and to diminish the amount stored in the soil to maintain springs. In an arid country like Utah, where the thirst of the air is not satisfied by the entire rainfall, any influence that will increase the rapidity of the discharge must also increase the amount of the discharge. The moisture that lingers on the surface is lost.
On the whole, it may be most wise to hold the question an open one whether the water supply of the lake has been increased by a climatic change or by human agency. So far as we now know, neither theory is inconsistent with the facts, and it is possible that the truth includes both. The former appeals to a cause that may perhaps be adequate, but is not independently known to exist. The latter appeals to causes known to exist but quantitatively undetermined.
It is gratifying to turn to the economic bearings of the question, for the theories best sustained by facts are those most flattering to the agricultural future of the Arid Region. If the filling of the streams and the rise of the lake were due to a transient extreme of climate, that extreme would be followed by a return to a mean condition, or perhaps by an oscillation in the opposite direction, and a large share of the fields now productive would be stricken by drought and returned to the desert.
If the increase of water supply is due to a progressive change of climate forming part of a long cycle, it is practically permanent, and future changes are more likely to be in the same advantageous direction than in the opposite. The lands now reclaimed are assured for years to come, and there is every encouragement for the work of utilizing the existing streams to the utmost.
And finally, if the increase of water supply is due to the changes wrought by the industries of the white man, the prospect is even better. Not only is every gain of the present assured for the future, but future gain may be predicted. Not alone are the agricultural facilities of this district improving, but the facilities in the whole Rocky Mountain Region are improving and will improve. Not only does the settler incidentally and unconsciously enhance his natural privilege, but it is possible, by the aid of a careful study of the subject, to devise such systematic methods as shall render his work still more effectual.