(a) Flood Losses Resulting From Periodic Inundation. The flood hazard areas of the City are subject to inundation which results in loss of life, property and health, safety hazards, disruption of commerce and governmental services, extraordinary public expenditures for flood protection and relief, and impairment of the tax base, all of which adversely affect the public health, safety and general welfare.
(b) General Causes of Flood Losses. Such flood losses are caused by the cumulative effect of obstruction in floodways causing increases in flood heights and velocities and the occupancy of flood hazard areas by uses vulnerable to floods or hazardous to others, which areas are inadequately elevated or otherwise protected from flood damage.
(c) Methods Used to Analyze Flood Hazards. This chapter uses a reasonable method of analyzing flood hazards, which method consists of a series of the following interrelated steps:
(1) Selection of a base flood which is based upon engineering calculations which permit a consideration of such flood factors as expected frequency of occurrence, the area inundated and the depth of inundation. The base flood selected for this chapter is representative of a large flood which is reasonably characteristic of what can be expected to occur on the particular streams subject to this chapter. Such base flood is in the general order of a flood which could be expected to have a one percent chance of occurrence in any one year, as delineated in the official Flood Plain Study and illustrative materials dated September 16, 1980, as amended, which Study is hereby incorporated by reference in this section.
(2) Calculation of water surface profiles based upon a hydraulic engineering analysis of the capacity of the stream channel and overbank areas to convey the base flood;
(3) Computation of the floodway required to convey this flood without increasing flood heights more than one foot at any point;
(4) Delineation of floodway encroachment lines within which no obstruction is permitted which would cause any increase in flood height; and
(5) Delineation of floodway fringe, i.e. that area which is outside the floodway encroachment lines but still subject to inundation by the base flood.
(Ord. 1114. Passed 2-23-88.)