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Show PART III CURRENT WATERSHED CONDITIONS AND PROBLEMS, AND EFFECTS OF PROBLEMS Wind erosion damage on cropland is mainly limited to sandy surface soils that are dry farmed. These soils are of minor extent in the region and are intermingled with other soils less subject to erosion. Damages consist of soil loss and injury to crops. Often stands are destroyed on exposed ridges. Soil drifts along fence lines and roads interfere with farming operations and increase production costs. Wind erosion on irrigated cropland is restricted to small local areas where highly erodible soils have been tilled and a crop has not been estab- lished. Erosion damage on Indian land is widespread in many small fields located adjacent to intermittent streams. These tracts are usually too small for modern economic methods of agriculture. Primitive irrigation methods, especially in isolated areas of Indian country, prevent adequate control of water diverted from sporadic, high-intensity runoff. Manage- ment difficulties resulting from poorly designed water control structures, lack of maintenance and insufficient farm equipment intensify the erosion problem. These cultivated lands generally lack protective cover between growing seasons and are subject to wind erosion. Some fields are not farmed regularly and are left exposed to wind action throughout the year. Irrigated soils with a high gypsum content present difficult manage- ment problems. Under irrigation the gypsum tends to dissolve and there is soil subsidence and piping. This produces eroding channels through fields and damages water distribution structures. Some of these severely eroded Indian lands are abandoned without stabilization treatment resulting in continued erosion and land loss. Erosion on urban and other land There is an estimated 929,000 acres of urban, buildup, rights-of- way, and transportation land within the region. Erosion is a problem on approximately 286,000 acres. Erosion within urban areas, farmsteads, and along highway and railroad rights-of-way varies from slight to locally severe. The larger centers of urban population are located in valleys where there are deep friable, alluvial soils that are susceptible to water erosion. Normal runoff patterns are drastically altered on urban land resulting in large flows in some drainageways. There is also an increased rate of runoff due to roofing and paving. These factors increase the erosion hazard. Accelerated water erosion resulting in rilling and gullying is of greatest economic consequence. Gullying and streambank cutting endanger fences, telephone and electric lines, roadways, culverts, and bridges. Replacements often must be made due to undercutting of established struc- tures. Urban housing developments are often subject to damage during the 31 |