FLOOD06826

• County: Statewide
• Basin: Statewide
• Title: National Economic Development Procedures Manual-Urban Flood Damage
• Date: 3/1/1988
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

secure the results of their observation and experience, is an inseparable

part of the procedure, Through the H&H studies, described above, and the
topographic studies necessary to outline the floodplain, there is a degree

of uncertainty as to where the limits of flooding would be for any

particular flood event. Some of that uncertainty can be overcome through

use of more detailed data and more precise procedures, Some of the

sources of uncertainty are unavoidable and can only be acknowledged, The

following conditions may be found to affect the limits and extent of

overflow areas and damages:

1) Duration of flooding;
2) Filling and scouring of stream channels, outlets, and confluences

during floods, to either increase or decrease channel capacity;

3) Observed or anticipated synchronization of flood peaks from

several tributary areas;

4) Effects of buildings, streets, embankments, other obstacles and

cuts on the course of flood flow;

5) Diversion of flood flows at various stages to other courses or

channels, and the probability of erratic or unpredictable paths;

6) Contribution of sediment, debris, ice, and other blockages;

7) Local aggravating circumstances affecting overflow, such as dams,

inadequate or clogged waterway openings, obstructions in

channels, pervious and impervious embankments, pervious
substratum, adequacy of local drainage and sewerage, inadequacy

of existing levees, and backwater conditions in channels; and,

6) A major stream or a tributary changing course, and causing the

flow of the water to take a different path.

V-20