A Beginner's Guide to ASCE 7-05

Chapter 6 - F_a: Flood Loads

© 2007, T. Bartlett Quimby

Section 6.1

Overview

Last Revised: 11/04/2014

Flooding has caused substantial damage to structures throughout time.  As civilizations have become more developed, the cost of flood damage has escalated dramatically.

In the United States, flooding has resulted such significant loss that Federal Emergency Management Agency (FEMA) has funded work to define flood risk and flood design methods to minimize economic loss as the result of flooding.  This work has resulted in defining flood risk, the loads to be expected in flood zones, and the building practices that are permitted for the various flood hazard zones.  The main driving force behind implementation of this work is the National Flood Insurance program.  A key component of the Flood Insurance program are the Flood Insurance Rate Maps (FIRMs). 

A FIRM defines zones of risk in a community.  Many of the maps can be obtained online from FEMA.   If you cannot find one on-line, then contact the building official that has jurisdiction over your site. To develop a FRIM, a hydrological study must be conducted to determine flooding risks and characteristics of the flooding.  This information is used to develop the risk zones and such data as the design flood elevations.  This information is necessary for predicting the loads that floods exert on structures.

Flooding is generally divided into two types:  riverine and coastal.  Riverine flooding results from rain events upstream and coastal flooding is closely associated with storm (wind) and seismic (including Tsunami) events.  Riverine flooding can also result from loss of integrity of upstream water storage facilities (mostly dams - both man made and natural).  Many of the hydrostatic and hydrodynamic principles are the same for both types of flooding.

While ASCE 7-05 has the requirements for Flood Loading, FEMA's Coastal Construction Manual (particuarly parts 11.6 and 11.7) does a very good job showing how to compute and apply the forces.  Much of the information presented here comes from this manual.