A flood occurs when a stream channel can no longer contain the water moving through it. Floods usually are local, short-lived events, others can be catastrophic, happening with little or no warning. Floods are most often caused by prolonged rainfall that saturates the ground causing surface runoff into nearby streams increasing their discharge. Flooding occurs when the water spills out of the channel and on to the adjacent terrain. Though viewed as a “natural hazard” to humans, flooding is a natural, rejuvenating process. It is a hazard to humans when we occupy flood-prone areas for living, recreation, or agriculture. To protect ourselves ,levees are constructed to restrict flow to the channel or a small portion of the natural floodplain. Levees can and do fail if not properly planned and constructed. Such was the case in New Orleans when it was hit by Hurricane Katrina. The catastrophic failure of the levee system has moved the United States government to undertake a survey of its existing levee system throughout the country.
When The Levees Fail
“The levee project is a comprehensive one, spanning four years and operating in three phases. In the first phase, researchers will identify potential technologies and procedures that can rapidly and affordably indicate problem locations along a levee, strengthen these existing areas, provide innovative designs for new levees, and repair any breaches. Subsequent phases will test and demonstrate the technologies and procedures. For instance, the U.S. Army Engineer Research and Development Center has developed the Levee Condition Assessment Technology, or LevCAT, which combines geophysical instrumentation with airborne and ground-based research to essentially “see” weak soil under levees.”
Image: Crevasse splay sand from levee break at Bryants Creek MO crossing floodplain of upper Mississippi River near mile 260. Photo by R.H. Meade, USGS (Source)