From the Susquehanna River in eastern Pennsylvania, through the Missouri and Mississippi River basins, to the American and Sacramento Rivers in California, and places in between, this nation faces a flood management problem. In particular, extreme weather events the last few years – including heavy snow, multiple 100-year-plus storm events, and tropical storms – have highlighted the inadequacy of dams, reservoirs, and levee systems, and the consequences of years of floodplain development.
According to an Associated Press report, the U.S. Corps of Engineers currently needs more than $2 billion to repair levees, floodwalls, and river banks damaged just this year, not including recent flood damage caused by Hurricane Irene and Tropical Storm Lee. Record rainfall in the Upper Midwest this spring, combined with already full flood-protection reservoirs, led to record high water levels and levee overtopping (or intentional breaching) along the Missouri and Mississippi Rivers. Much more money is needed to upgrade flood-protection structures across the county to withstand a 100-year or greater storm (see “Corps conundrum,” CE News, June 2011, page 8).
According to a 2010 nationwide survey by HNTB Corporation, 40 percent of Americans think that state governments should have the primary responsibility for managing flood system improvements; 23 percent want the federal government to shoulder this responsibility, and only 10 percent think private owners should take responsibility. Fifty-one percent of survey respondents said that city and state money should fund these improvements.
But such a piecemeal approach – city and state management – could complicate the delicate balance of upstream and downstream impacts from levees built along one stretch of a river to protect a large urban area. “We need a balanced, systematic approach that prioritizes risk and strikes a balance between flood control, protecting the environment, and reviving our economy,” said Rob Vining, national director for HNTB’s water resources practice.
Of course, even with funding, civil engineers also face local challenges in building or improving levees. For example, efforts to improve critical levees along the American and Sacramento Rivers in Sacramento, Calif., have encountered landowner opposition, endangered species habitats, and technical issues such as hydrologic and hydraulic modeling to determine proper levee height and finding sufficient amounts of adequate soil, according to Paul Enneking, PLS, vice president, director of surveying and mapping at Psomas and project director for surveying and right-of-way services for the Sacramento Area Flood Control Agency (see “Special Report: Protecting urban areas from flooding” on page 50).
Remarkably, one problem, at least in California, is the lack of public awareness about how much the state has become dependent on its levee systems. According to a 2011 HNTB survey, 37 percent of the state’s residents think that there are no levees in California, when in fact, the Sacramento-San Joaquin Delta has 1,600 miles of levees that have experienced at least 162 failures, HNTB said.
“Failure of the earthen levees in the Sacramento-San Joaquin Delta alone would not only cause overwhelming devastation to homes and businesses in the region; it also could result in the loss of the state’s biggest source of fresh water for at least a year and a half,” Vining said.
According to HNTB’s 2010 nationwide survey, 68 percent of Americans do not recognize that flooding is the biggest natural threat to their home or property. Unfortunately, it’s likely to take continued extreme snow and rain events and consequent flooding across the country, or flood zone remapping by the Federal Emergency Management Agency and consequent jumps in flood insurance rates and deflated property values to get the public’s attention.