8 - Flooding


In this unit we will define a flood as being the temporary overflow of a river onto adjacent lands not normally covered by water. Inundation by the sea is another type of flood but we already discussed this in the unit on coastal disasters (Unit 6) so we will focus on river flooding here.  Throughout history humans have lived along rivers mostly because they are sources of water for drinking, irrigation, fishing and industry. Rivers also provide transportation routes, energy, and a means of waste disposal. Add to this, the fact that river valleys often have flat land suitable for agriculture and flooding in these environments is one of the more common and costly types of natural disasters.

Learning Objectives

Upon completion of this unit you should be able to:

1. Describe the water cycle and all of it's major components.
2. Explain what the "discharge" and "gradient" of a river mean.
3. Explain the major differences between upland rivers and those flowing in lowland areas.
4. Define "lag-time" and how this is important for flood danger in various areas.
5. List the important primary and secondary effects of river flooding
6. Describe what "competency" means and how this relates to the type and amount of sediment a river carries.
7. Describe the important features of a flash flood.
8. List several different ways in which flash floods can be generated and be able to describe some of the case histories of flash floods.
9.  Recognize geological environments where large dams should not be built and why.
10. Describe the important features of a regional flood.
11. List the main cause of regional flooding as well as some things that can make the problem worse
12. Describe the unique problems related to flooding on the Huang He in China as well as some possible solutions?
13. Describe the way in which water flow in the lower Mississippi River is controlled and some of the problems that would result if these control measures fail.
14. Predict river flooding in any given location. Is it likely to happen or not?
15. Analyze the urban landscape and determine whether downstream flooding is likely to increase as a result of development.
16. List various ways in which flood hazard can be reduced by channel modifications.
17. List various ways in which we can protect ourselves from flood danger using regulation.

Required Readings

Abbott, P.L., 2014. Natural Disasters, Ninth Edition:

Readings From the Old Book

Abbott, P.L., 2012. Natural Disasters, Eighth Edition:

Glossary Terms

Arched Structure Monsoon Rain
Avulsion Natural Levee
Central Himalayan Seismic Gap Old River Control Structure
Competency Plastic (Clay)
Constructed Levee Rapids
Cross-Sectional Area Red River
Delta Regolith
Discharge Reinforced Concrete
Distributary Richter Magnitude 
Gradient Runoff
Himalaya South Fork Dam
Huang He Storm Sewer
Ice Jam Suspended Sediment
Lag Time Topography
Loess Tributary
Log Jam Vaiont Dam
Low Sill Structure