Report on the lands of the arid region of the United States, with a more detailed account of the lands of Utah

by John Wesley Powell; Willis Drummond; Clarence E. Dutton; Grove Karl Gilbert; A. H. Thompson

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.