Flooding is the most commonly experienced natural hazard. Although we cannot prevent floods from happening, individuals can be better prepared. Table 8.2 summarizes what individuals can do to prepare for a flood as well as what not to do.
8.11 Perception of Flooding
At the institutional level—that is, at the government and flood-control agency level—perception and understanding of flooding are adequate for planning pur-poses. On the individual level, however, the situation is not as clear. People are tremendously variable in their knowledge of flooding, anticipation of future flooding, and willingness to accept adjustments caused by the hazard.
Progress at the institutional level includes mapping of flood-prone areas (thousands of maps have been prepared), of areas with a flash-flood potential downstream from dams, and areas where urbanization is likely to cause prob-lems in the near future. In addition, the federal government has encouraged states and local communities to adopt floodplain management plans.8Still, plan-ning to avoid the flood hazard by not developing on floodplains or by relocating
Perception of Flooding 281 Typical zoning map before and after the addition of flood regulations.(From Water Resources Council. 1971. Regulation of flood hazard areas, vol. 1)
P R E L I M I N A R Y P R O O F S Unpublished Work © 2008 by Pearson Education, Inc.
From the forthcoming book Introduction to Environmental Geology, Fourth Edition, by Edward A. Keller, ISBN 9780132251501. To be published by Pearson Prentice Hall, Pearson Education, Inc., Upper Saddle River, New Jersey. All rights
TABLE 8.2 What to Do and What Not to Do before and after a Flood
Preparing for a Flood
• Check with your local flood control agency to see if your property is at risk from flooding.
• If your property is at risk, purchase flood insurance if you can and be sure that you know how to file a claim.
• Buy sandbags or flood boards to block doors.
• Make up a Flood Kit, including a flashlight, blankets, raingear, battery-powered radio, first-aid kit, rubber gloves, and key personal documents. Keep it upstairs if possible.
• Find out where to turn off your gas and electricity. If you are not sure, ask the person who checks your meter when he or she next visits.
• Talk about possible flooding with your family or housemates. Consider writing a Flood Plan, and store these notes with your Flood Kit.
• Underestimate the damage a flood can do.
When You Learn a Flood Warning Has Been Issued
• Be prepared to evacuate.
• Observe water levels and stay tuned to radio and television news and weather reports.
• Move people, pets, and valuables upstairs or to higher ground.
• Move your car to higher ground. It takes only 0.6 m (2 ft) of fast-flowing water to wash your car away.
• Check on your neighbors. Do they need help? They may not be able to escape upstairs or may need help moving furniture.
• Do as much as you can in daylight. If the electricity fails, it will be hard to do anything.
• Keep warm and dry. A flood can last longer than you think, and it can get cold. Take warm clothes, blankets, a Thermos, and food supplies.
• Walk in floodwater above knee level: it can easily knock you off your feet. Manholes, road works, and other hazards may be hidden beneath the water.
After a Flood
• Check house for damage; photograph any damage.
• If insured, file a claim for damages.
• Obtain professional help in removing or drying carpets and furniture as well as cleaning walls and floors.
• Contact gas, electricity, and water companies. You will need to have your supplies checked before you turn them back on.
• Open doors and windows to ventilate your home.
• Wash water taps and run them for a few minutes before use. Your water supply may be contaminated; check with your water supplier if you are concerned.
• Touch items that have been in contact with the water. Floodwater may be contaminated and could contain sewage. Disinfect and clean thoroughly everything that got wet.
Source: Modified after Environment Agency, United Kingdom. Floodline accessed 11/1/00 at www.environment_agency.gov.uk/flood/press_2.htm What Not to DoWhat to DoWhat Not to DoWhat to DoWhat Not to DoWhat to Do
present development to locations off the floodplain needs further consideration and education to be accepted by the general population. This was tragically shown by the 2006 floods in the Mid-Atlantic United States, when severe river flooding impacted the region from Virginia to New York (Figure 8.34). Over 200,000 floodplain residents were evacuated in Pennsylvania alone and damages exceeding $100 million were incurred. About 16 people lost their lives as cars were swept away by floodwaters and people drowned in flood-swollen creeks and rivers. About 70 people were rescued from rooftops. As a people we need to just “say no” to future development on floodplains. That is the most cost-effective way to reduce chronic flooding.
P R E L I M I N A R Y P R O O F S Unpublished Work © 2008 by Pearson Education, Inc.
From the forthcoming book Introduction to Environmental Geology, Fourth Edition, by Edward A. Keller, ISBN 9780132251501. To be published by Pearson Prentice Hall, Pearson Education, Inc., Upper Saddle River, New Jersey. All rights reserved. This publication is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic,
Figure 8.34 Mid-Atlantic floods of June–July 2006 (a) Map of major and minor flooding.(Modified from New York Times with data from National Weather Service)(b) Collecting mail from a flooded home in Wilkes-Barre, Pennsylvania.(AP/Wide World Photos)
major flooding minor flooding TOTAL RAINFALL JUNE 24–28, 2006
NEW YORK
PENNSYLVANIA
Delaware River
MARYLAND NEW
JERSEY
Trenton
DEL.
VIRGINIA W. VA.
0 25 50 mi 0 40 80 km
RIVER CONDITIONS (43 cm) 17”
(25 cm) 10”
(13 cm) 5”
(5 cm) 2”
Binghamton
Wilkes-Barre Susquehanna
River N
(a)
(b)
P R E L I M I N A R Y P R O O F S Unpublished Work © 2008 by Pearson Education, Inc.
From the forthcoming book Introduction to Environmental Geology, Fourth Edition, by Edward A. Keller, ISBN 9780132251501. To be published by Pearson Prentice Hall, Pearson Education, Inc., Upper Saddle River, New Jersey. All rights
SUMMARY
Streams and rivers form a basic transport system of the rock cycle and are a primary erosion agent shaping the land-scape. The region drained by a stream system is called a drainage basin.
Sediments deposited by lateral migration of meanders in a stream and by periodic overflow of the stream banks form a floodplain. The magnitude and frequency of flooding are inversely related and are functions of the intensity and distri-bution of precipitation, the rate of infiltration of water into the soil and rock, and topography. Flash floods are produced by intense, brief rainfall over a small area. Downstream floods in major rivers are produced by storms of long duration over a large area that saturate the soil, causing increased runoff from thousands of tributary basins. Urbanization has increased flooding in small drainage basins by covering much of the ground with impermeable surfaces, such as buildings and roads, that increase the runoff of stormwater.
River flooding is the most universally experienced natural hazard. Loss of life is relatively low in developed countries that have adequate monitoring and warning systems, but property damage is much greater than in prein-dustrial societies because floodplains are often extensively developed. Factors that control damage caused by flooding include land use on the floodplain; the magnitude and frequency of flooding; the rate of rise and duration of the flooding; the season; the amount of sediment deposited; and the effectiveness of forecasting, warning, and emergency systems.
Environmentally, the best solution to minimizing flood damage is floodplain regulation, but it will remain necessary to use engineering structures to protect existing development in highly urbanized areas. These include physical barriers such as levees and floodwalls and structures that regulate the release of water, such as reservoirs. The realistic solution to minimizing flood damage involves a combination of flood-plain regulation and engineering techniques. The inclusion of floodplain regulation is critical because engineered structures tend to encourage further development of floodplains by pro-ducing a false sense of security. The first step in floodplain regulation is mapping the flood hazards, which can be diffi-cult and expensive. Planners can then use the maps to zone a flood-prone area for appropriate uses. In some cases, homes in flood-prone areas have been purchased and demolished by the government and people relocated to safe ground.
Channelization is the straightening, deepening, widening, cleaning, or lining of existing streams. The most commonly cited objectives of channelization are flood control and drainage improvement. Channelization has often caused environ-mental degradation, so new projects are closely evaluated.
New approaches to channel modification using natural processes are being practiced, and in some cases channelized streams are being restored.
An adequate perception of flood hazards exists at the institutional level. On the individual level, however, more public-awareness programs are needed to help people clearly perceive the hazard of living in flood-prone areas.