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<br />11 <br /> <br />also what State and local govenrrnental agencies may have in their <br />statutes, regulations, ordinances, maps, etc., by going into investigation <br />of data sourCeS further than was done under Guideline 1. <br /> <br />Also, before adopting either approach, the agency should consider <br />its own resourCeS and whether it would be better to make its own <br />evaluation, or whether assistance should be requested from one of <br />the agencies named in Section 3 of Executive Order 11296 or other <br />appropriate source. <br /> <br />(3)..... USE THE FOLLOWING TO IDENTIFY AND EVALUATE <br />THE FLOOD HAZARD: <br /> <br />(3A.)..... THE 100- YEAR FLOOD AS THE BASIC FLOOD: <br /> <br />(3B. ). . . .. THE FLOOD HAZARD ZONE, DEFINED AS THE <br />AREA INUNDATED BY THE BASIC FLOOD: <br /> <br />(3C 1)..... IN THE PLAN APPROACH A FLOODWA Y, <br />DEFINED AS THE PORTION OF A RIVERINE FLOODPLAIN NEEDED <br />TO CONVEY A BASIC FLOOD, WITH NOT MORE THAN ONE <br />FOOT RISE IN FLOODWATER ELEVATION; OR <br /> <br />(3C 2).... .IN THE CASE APPROACH A PROCEDURE TO <br />ASSURE THAT ANY ENCROACHMENT ON THE FLOODPLAIN WILL <br />PERMIT CONVEYANCE OF THE BASIC FLOOD WITHOUT INCREASING <br />FLOOD HEIGHTS OR VELOCITIES TO AN EXTENT WHICH WOULD <br />CAUSE SIGNIFICANT UPSTREAM OR DOWNSTREAM DAMAGE TO <br />EXISTI~G OR REASONABLY ANTICIPATED FUTURE DEVELOPMENT. <br /> <br />(3D. ). . . . . FLOODS GREA TER OR LESS THAN THE BASIC <br />FLOOD AS APPROPRIA TE. <br /> <br />Basic Flood. The 100-year flood has a magnitude that may be equaled <br />or exceeded once every hundred years, on the average. It is also <br />called the IOO-year frequency flood, or the 1 percent chance flood <br />(it has 1 chance in 100 of being equaled or exceeded in any given year), <br />or else it is said to have a 100-year recurrence interval. Other floods <br />having a designated frequency should be similarly treated. In all <br />cases, all of the conditions affecting flows should be a part of the <br /> <br />~ <br />~ <br />