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Show PART III CURRENT WATERSHED CONDITIONS AND PROBLEMS, AND EFFECTS OF PROBLEMS early stages of construction. Earth moving operations connected with site preparation and excavations for basements disturb the land surface and leave it bare. Runoff from storms can then cause severe erosion. Water erosion damage of urban land along highways and roads is greater in the foothills and mountainous parts of the region due to steep slopes and higher precipitation. Construction activities also disturb a larger surface area than in the lower valleys. Wind erosion on urban land is significant only in the arid and more sparsely populated parts of the region. Wind-blown sand and silt damages landscaping, buildings, and vehicles. The local residents must also endure the physical discomfort and health hazards accompanying dust storms. Flood and Sediment General conditions and effects Flood damage is closely interrelated with erosion damage and sedi- mentation damage. Large flows of water during spring runoff and from high intensity summer rains carry soil particles and debris downstream where they are deposited and cause damage. Flood waters can also cause damage to vegetation, structures, injuring or killing animal and human life, and by disrupting transportation and communication facilities. Many economic losses are caused by sediment. Sediment deposited on flood plains damages crops, clogs irrigation and drainage ditches, impairs surface drainage, affects soil productivity and makes land leveling or other repair operations necessary. Storage capacity of reservoirs is depleted due to filling and mechanical equipment such as pumps and generators are damaged. Sediment destroys fish habitats and the aesthetic values of water and shore lines thus impairing recreational opportunities. A more detailed discussion of the detri- mental effects of sediment on water quality is contained in Appendix XV - Water Quality, Pollution Control, and Health Factors. |