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<br />e <br /> <br />e <br /> <br />e <br /> <br />1998. &O/11,ado Flood Hazard Mitigation Plan (409) <br /> <br />The causes of floods relate directly to the accumula- <br />tion of water from precipitation or the failure of man- <br />made structures ~uch as dams or levees. Floods <br />caused by precipitation are further classified as com- <br />ing from: <br /> <br />. Rain in a general stwm system <br /> <br />. Rain in a IocaOzed intense thunderstorm <br /> <br />. Melting snow <br /> <br />. Rain on melting snow <br /> <br />. Ice jams <br /> <br />Rainfall and melting snow in the mountains feed four <br />major river systems with headwaters in Colorado. <br />These are the, Missouri, Arkansas, Rio Grande, and <br />Colorado River basins. These basins encompass <br />many small streams and rivers as shown in Figure <br />2.2. <br /> <br />Precipitation in each basin is related to the seasons <br />and !\No major sources of moisture. Summer showers <br />and thunderstorms that occur from June through <br /> <br />September primarily are caused by moisture from the <br />Gulf of Mexico or the Pacific Ocean. During the fall, <br />occasional general rainstorms and thunderstorms 0c- <br />cur from wet and warm cyclonic air masses, which <br />move in from the southem Pacific Ocean. Winter and <br />spring rain and snow storms are generally a result of <br />moist air masses which originate in the cooler northern <br />Pacific Ocean and move inland across the Pacific <br />Northwest <br /> <br />Floods caused by failure of man made structures are a <br />result of: <br /> <br />. Hydrologic deficiencies <br /> <br />. structural deficiencies <br /> <br />. lmproper Operation or Sabotage (1 case in CO) <br /> <br />Each of these causes results in floods, which hal/e <br />distinct characteristics relative to rate of rise, volume, <br />duration, and flood season. <br /> <br />'09" <br />41 -r-" <br />I <br /> <br />uS' 107- <br /> <br />106' tW loe. 103- <br /> <br />--- ..--- ----- <br /> <br />II' <br /> <br /> <br />l1' <br /> <br />109" <br /> <br />106" <br /> <br />.".u__--'.-.._ . .....<__~~_ _~=,_.....;:.;.__'__:..: '.-;"",,~~_'~_'.:......:..:..----:. <br /> <br />.-.:.~--~.'.,;:.-:....,.:.:.....,,"::.;;~:;':'~~':'- <br /> <br />106" <br /> <br />lor <br /> <br />FiIe~.2.pufJ <br /> <br />102" <br /> <br />.... <br /> <br />39' <br /> <br />38' <br /> <br />-..-- --- <br /> <br />I <br />, <br />I <br />I <br />I <br />I <br />,. <br />102" <br /> <br />105' <br /> <br />104" 1(J,~ <br />FigIIIe 2-2 <br /> <br />Chapter 2 . 2 <br /> <br />11Z11116:14 AM <br />