Changes in runoff and sediment yield caused by changing sagebrush cover to grass cover were studied at four small watersheds in western Colorado during a 9-year period. Measurements of runoff and sediment yield from four watersheds were made for 3 years, at which time two watersheds were plowed and seeded to beardless bluebunch wheatgrass. The same measurements were then continued for an additional 6 years.
Measurements indicated that conversion to grass caused a reduction in runoff from summer rainstorms of about 75 percent. Runoff from spring snowmelt increased about 12 percent and annual runoff from treated watersheds decreased about 20 percent when compared to control watersheds. Sediment yield from the seeded watersheds was reduced by about 80 percent. Most of this reduction is related to the decrease in runoff from summer rainstorms.
The size of barren interspaces between plants was reduced on the converted watersheds to about 30 percent of those on the untreated watersheds. Linear regression analysis indicates that a reduction of 38 percent in the amount of bare soil resulting from planting grass would result in a decrease of 73 percent in sediment concentration.
