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<br />. <br /> <br />. <br /> <br />. <br /> <br />8. Flood Damaqes. <br /> <br />. <br /> <br />Plate 2 also shows the without-project 100- and 500-year <br />flood plains for the area within the study reach prone to <br />flooding by the Colorado River. Because the floods would be <br />relatively shallow with fairly low velocities, the risk of loss <br />of life as a direct result of a flood would be low. However, <br />damages to structures and their contents in the flood plain would <br />be a problem. <br /> <br />Major flood damages historically have been limited to <br />erosion. Emergency flood fighting efforts have successfully <br />forestalled significant inundation damages. Under existing <br />conditions, inundation damages would consist mainly of damages to <br />176 structures. An estimated l09 structures, including 106 <br />residential and 3 non-residentia~ are within the 100-year flood <br />plain on the north side of the river (Riverside), and 67 <br />residences are on the south side of the river (Rosevale). <br /> <br />Damage to residences would consist of structure and content <br />damage. outside landscaping, outbuildings, and vehicles could <br />also be damaged to a lesser extent. Cleanup of debris and <br />sediment would also be a cost on both private and public grounds. <br />utilities and street pavements could also be affected. Other <br />costs associated with a flood would include floodfighting, <br />traffic routing, police protection, evacuation, and temporary <br />sheltering. Annual costs associated with flood plain occupancy <br />include flood insurance premiums. <br /> <br />Flood damages were developed individually for each side of <br />the river. This was done in recognition of the differences in <br />community infrastructure and differences in potential for flood <br />control solutions for the separate communities. <br /> <br />It is estimated that flood damages begin at about a 10-year <br />frequency event. Flood damages were computed for the 10-, 50-, <br />lOO-, and 500-year floods. Flood damages for other frequencies <br />were then interpolated, and the resulting curve was used to <br />determine average annual damages by the use of standard <br />integration techniques. The computations were based on 1990 <br />price levels. Mesa County is currently experiencing a very mild <br />economic recovery from the bottoming of the oil shale industry- <br />related economic boom of the early 1980's. Housing prices, <br />either residential or commercial-industrial, are rising at only a <br />very modest pace; hence, estimated values for structure costs <br />will not significantly change in a period of a year or two. <br /> <br />Historical damages have not been estimated. Floodfighting <br />costs, damages, and cleanup were not recorded separately for the <br />study reach and in most cases are not complete. The public works <br />superintendent for Grand Junction stated that generally the bulk <br />of flood-related costs are incurred after the flood event, and <br /> <br />7 <br />