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TABLE OF CONTENTS Page I. INTRODUCTION . . . . . . . . . . . . . . . . . . . I-1 II. NATIONAL FLOOD INSURANCE PROGRAM BACKGROUND II-1 III. APPLICABLE NATIONAL FLOOD INSURANCE PROGRAM FLOODPLAIN MANAGEMENT REQUIREMENTS IN APPROXIMATE ZONE A AREAS . III-1 Requirements for obtaining Base (lOO-year) Flood Elevation Data . . . . . . 0 .. . III-1 Requirements for Developing Base (lOo-year) Plood Elevation Data . . 0 0 . 0 0 0 .. III-2 Use of Draft or preliminary Plood Insurance Study Data . . 0 . . . . . 0 0 0 0 . . 0 0 0 III-7 Advantages of Developing Base (lOo-year) Flood Elevation Data . . . . . . 0 . . . . . 0 0 III-8 IV. OBTAINING EXISTING BASE (lOO-YEAR) FLOOD Federal Emergency Management Agency . Other Federal Agencies . . . . . . . Other State and Local Agencies . . . ELEVATIONS IV-1 IV-1 IV-3 IV-4 V. DEVELOPING BASE (lOO-YEAR) FLOOD ELEVATIONS Simplified Methods . . . Contour Interpolation .... Data Extrapolation . . . . . . V-1 o 0 0 V-1 o 0 0 V-2 o 0 0 V-7 Detailed Methods 0 0 . 0 . . 0 0 0 0 0 . 0 V-11 Topography 0 O. .. 0 0 . 0 0 0 V-ll Existing Topographic Maps 0 V-ll Datum Requirements for Field Surveys 0.. V-12 Number of Cross Sections Required 0 0 . V-13 Proper Location of Cross Sections . 0 0 V-13 Hydrology 0 0 . 0 . 0 . 0 0 0 0 0 0 0 0 0 . 0 0 0 V-15 DiSCharge-Drainage Area Relationships 0 0 0 V-16 Regression Equations . 0 0 .. 0 0 0 0 0 V-19 TR- 5 5 . . . 0 0 0 0 . O. 0 0 . 0 0 V - 20 Rational Formula . 0 0 0 0 0 0 0 0 0 0 0 0 0 V-20 Other Hydrograph Methods 0 0 0 0 0 0 0 0 0 0 V-21 Hydraulics 0 0 0 . . 0 . 0 0 0 0 0 0 . 0 0 0 0 0 V-22 Normal Depth . 0 . 0 0 . . . 0 0 0 0 0 00 V-23 Critical Depth . . 0 0 0 0 . . . 0 0 0 0 0 0 V-26 Step-BaCkwater Analysis . . . . 0 0 0 . . 0 V-28 Hydraulic Structures O. 0 . . 0 0 0 . V-28 VI. OBTAINING LETTERS OF MAP CHANGE . . . . . . . . . VI-l ii