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<br />~ <br /> <br />.--- <br /> <br />Average rainfall during April, May and June on the <br />Western Slope varies from 2 to 4 inches; on the Eastern <br />Slope rainfall averages run as high as 6 to 8 inches during <br />the 3 months. When this rainfall is concentrated during the <br />run off period, flooding is likely. <br /> <br />. <br /> <br />Earthquakes <br /> <br />Earthquakes are caused by faul t movements wi thin the <br />earth that produce a sudden motion or shaking of the earth's <br />surface. In the 120 years that modern man has occupied <br />Colorado, hundreds of earthquakes have been noted. In the <br />early years there were "felt" reports, but more recently <br />seismographic instruments have been used to detect and <br />locate earthquakes. Geolog ists recognize that many of the <br />State's mountain ranges and bas ins are youthful and that <br />faults associated with them continue to move and have the <br />potential for generating earthquakes. Analyzing both the <br />potential for movement of these faults and past earthquake <br />history indicates the potential for damaging earthquakes has <br />been underestimated in the past and that a potential exists <br />for greater damage then expected. <br /> <br />"'--' <br /> <br />Large earthquakes and even moderate-sized events can <br />damage or destroy the works of man by severe ground shaking, <br />ground rupture, or displacement near the fault zone or by <br />ground failure from landslides, soil settlement, soil <br />liquefaction, and ground cracking. Additional damage and <br />health hazards can be caused by earthquake induced dam <br />failure, ruptured gas lines, water and sewage disposal <br />facilities, and electrical power lines. Many critical <br />structures (dams, hospitals, schools) have not been ade- <br />quately designed for larger sized earthquakes that now <br />appear possible in Colorado. Another area for attention is <br />related to the fact that most local building codes continue <br />to show a low risk seismic zonation which does not appear <br />adequate for much of the State of Colorado in view of the <br />emerging better understanding of our earthquake hazard <br />(Colorado Geological Survey). <br /> <br />. <br /> <br />Dam Failure Flooding <br /> <br />Approximately 2,249 dams exist in Colorado that exceed <br />10 feet in height. Many of these pose considerable threat <br />to population who live downstream from them. These dams are <br />a particular threat when flash flooding occurs in the <br />vicinity of the dam, causing a sudden flow of water over <br />the spillway of the dam or over the dam. Some of the dams <br />in question are old and are subject to failure under extreme <br />flooding conditions. Many dams were built to store water <br /> <br />'- <br /> <br />6 <br /> <br />. <br />