Even with all the recent focus on issues with the Delta, I would expect a large majority of people living in California have no idea how levees impact their lives. Most may understand that levees are typically engineered and designed to provide flood protection for homes, businesses, and agriculture, but they may not realize they can also be used to convey or store water for domestic use, recharge, treatment, etc. In some cases, such as in the Delta, they play a pivotal role in securing a reliable supply of water by protecting the water from possible contamination (such as salt water intrusion).
A key aspect to levees is, once constructed, they are relied upon for land planning, become part of the natural landscape, and are very difficult to remove without significant impacts. There are more than 13,000 miles of levees in California that are designed and constructed to provide flood protection against a designated level of flooding, but they do not protect against all flooding. Levees can therefore provide a false sense of security that properties behind levees are “flood-proof”.
Risk associated with levee failure is a function of both the probability of a failure occurring and the consequences of that failure. Even if the probability of failure of a levee or levee system is lowered through rehabilitation or reconstruction, the overall risk may not be substantially reduced if the rehabilitation results in the construction of additional homes or businesses in the protected area. The probability of exceeding a levee’s design flood frequency is cumulative with time. For instance, over a 30 year period a levee that is designed for a flood that has a one percent annual exceedance probability (i.e., a “100-year flood”), has a 26 percent probability of experiencing a flood larger than the design flood.
A large part of the 13,000 miles of levees in California, particularly those in the Delta, suffer from poor maintenance, and have not been upgraded to account for current hydrology or changes in design criteria, let alone potential impacts associated with climate change. The damage caused by failure of a levee system can be catastrophic and could include loss of life, personal property, and prime agricultural land, and in the case of the Delta, could temporarily or permanently impact the security and reliability of much of California’s potable water supply.
Whether you live behind a levee or not, levee construction and rehabilitation are key components to providing a safe, reliable supply of water to meet California’s growing needs, as well as means to protect our citizens, personal property, and prime agricultural lands from the effects of floods. In order to maintain and enhance this protection, we need the following:
- Development of a National Levee Safety Program that includes all of the recommendations of the National Committee on Levee Safety;
- Incorporation of risk into the basis of design for levees and levee rehabilitation projects;
- Revision of the current USACE standards for levee vegetation to consider the potential benefits of levee vegetation, especially with respect to CEQA and NEPA compliance;
- Usage of the most recent guidance documents from DWR and USACE as a minimum standard for the evaluation, design, and construction of levees until such time as National and/or State standards are available;
- Action by Congress to address the growing potential for public and private liability for future damages resulting from levee failures.
The proper design, construction, maintenance and rehabilitation of levees is critical to providing protection to our homes, business, agricultural and recreation areas, as well as the water supply for over 25 million people (two-thirds of all Californians) and 3 million acres of farmland in California (supporting the production of 45% of all fruits and vegetables in the US).
For more information on California’s water crisis, read ACEC California’s latest issues of Engineering and Surveying Business Review at the link below. You will find articles about the severe drought that continues to impact the entire state and ACEC California members offer potential solutions to our state’s water woes.