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<br /> <br />Table I, cont.: Reducing Flood Losses in High Risk Areas. <br /> <br />Hazard <br /> <br />Special <br />Risk <br />Factors <br /> <br />Area of <br />Occurrence <br /> <br />Management Options <br /> <br />Ground <br />F ai/ure: <br />Subsidence <br /> <br />* Structural <br />damage and! <br />or collapse <br />* Permanent <br />inundation <br />* Increasing <br />flood <br />elevations <br />(over time) <br />* Damage to <br />buildings, <br />roads and <br />service <br />lines <br /> <br />Houston! <br />Galveston, <br />New Orleans, <br />Sacramento <br />Delta, and <br />many other <br />areas <br />(localized) <br /> <br />* Prepare maps showing mines, organic <br />soils, karst formations, areas subject <br />to hydrocompaction, etc. <br />* Conduct frequent site inspections <br />and restudies to determine currently <br />expected flood levels and revise 100- <br />year flood protection elevations. <br />* Require pre-development site <br />in vestiga tions. <br />* Prohibit development in high risk <br />areas; require adequate foundation <br />support through zoning or building <br />codes in other areas. <br />* Add freeboard to 100-year flood <br />eleva tions. <br />* Limit ground water, oil & gas <br />withdrawal where it is causing <br />subsidence; computer models can <br />predict subsidence related to amount <br />of withdrawal. <br />* Require reinjection of water <br />in oil & gas drilling operations. <br />* Purchase and relocate structures out <br />of high risk areas. <br /> <br />Ice Jam <br />Flooding <br /> <br />* Unexpected <br />flood levels <br />* Suddenness <br />* High velocity <br />* De bris <br />(ice floes) <br /> <br />Principally 35 <br />northern sta tes <br />including <br />Alaska; jams <br />occur most <br />often at <br />constriction <br />points in <br />river valleys <br /> <br />* Collect historical data on ice jam <br />floods; use it or engineering studies <br />to map ice jam inundation areas, <br />* Adopt setback lines. <br />* Require additional freeboard to <br />protect against ice. <br />* Adopt construction standards, esp- <br />ecially for floodproofing, that <br />consider ice damage. <br />* Acquire hazardous lands and relocate <br />structures that cannot be protected. <br />* Develop a warning system and <br />emergency action plan. <br />* Undertake remedial engineering <br />measures. <br /> <br />B-5 <br />