Details:

Creators:
Wood, Clinton M. ; Bernhardt, Michelle ; Moody, Tim ; Kouchaki, Behdad ; Rahimi, Salman
Wood, Clinton M. ; Bernhardt, Michelle ; Moody, Tim ; Kouchaki, Behdad ; Rahimi, Salman Less -
Corporate Creators:
University of Arkansas, Fayetteville
Corporate Contributors:
Maritime Transportation Research and Education Center ; United States. Dept. of Transportation
Maritime Transportation Research and Education Center ; United States. Dept. of Transportation Less -
Subject/TRT Terms:
[+]
Field Studies Geophysics Levees Research Hub Testing
Resource Type:
Tech Report
Geographical Coverage:
Arkansas ; United States
Arkansas ; United States Less -
Corporate Publisher:
University of Arkansas
Abstract:
Beginning with the first recorded levee construction in 1717 for the small village of New Orleans (Mitchell 1990), the United States levee system has been continuously adapted to respond to changing flood conditions and urban development. Although numerous flood related failures have occurred throughout history, prior to 2005, most of these failures were in low-risk rural areas where damages were mostly agricultural related. The first real failure to occur in an urban environment came in August of 2005 during Hurricane Katrina. The levees and floodwalls in and around New Orleans, Louisiana failed in over 50 locations, flooding more than 80% of the city, killing over 1,118 people, and resulting in an estimated $16.5 billion in damages (ASCE 2007). Considered the most costly US natural disaster on record, these events exposed the vulnerability and increased risk associated with levee systems surrounding growing urban developments. In 2007, Congress directed agencies to create a national levee database and in 2009 the American Society of Civil Engineers (ASCE) created a new category for levees in its report card for America’s infrastructure. Levees received a grade of D-, which was a less than poor rating, but it increased awareness of the issue, the limited funds available, and provided a general plan to address the deteriorating system. Before the next report card was released, two additional major flood related disasters occurred in the Midwest in 2008 ($538 million in estimated damages) and in 2011 where record water levels resulted in over $2 billion in damages and repairs (ASCE 2013). In the 2013 report card for America’s infrastructure, the American Society of Civil Engineers gave the levee system in the United States the same overall rating of D-, showing no change from the previous report. Although levee failures in the United States account for more economic impact than any Tech Report geo-related disasters, little improvement has been made to the overall levee system. This could prove to be a major problem in the coming decades, where continued deterioration, urban development, and an increase in extreme weather events will test these structures to and beyond their capacity and significantly increase the risk associated with their failure. The problem is twofold with the common link being a lack of monetary funds. Firstly, there is no single database documenting the existing levee systems and their conditions. The report card rating is based in part on information from the National Levee Database (NLD) which is comprised of approximately 14,700 miles of levees operated by the U.S. Army Corps of Engineers (USACE). The NLD only contains levees which are designed, maintained, and inspected by USACE and it currently neglects over an estimated 85% of the nation’s levees, which are locally owned and operated. It is estimated that approximately 100,000 miles of levees exist within the United States, affecting all 50 states and more than 43% of the population; however, the true extent is still unknown and gathering data from various owner entities is difficult. In fact, the Federal Emergency Management Agency (FEMA) manages the Midterm Levee Inventory (MLI) which contains roughly 35,600 miles of levees; however, the condition of many of these levees is unknown. Although the two agencies are working to combine the databases, limited funding is available to assess the condition of the levees. Without the condition and performance evaluation of a particular levee, there is no way to determine the risk associated with it. Typically, levees are evaluated based on a simple visual inspection program to identify critical or weak spots in the levee system (USACE 2014). This method can detect surface distress or erosion failures (post failure), but it cannot identify defects that exist within the inner core or foundation soil that could lead to a failure during an extreme event. This leads to a passive detection system that requires failures to occur before they are investigated and repaired. The methods currently used to proactively obtain this internal soil data are extremely time intensive, they require soil borings or 2 sampling which damages the levees, and they only provide a small discrete amount of data. With the limited funds available, it would be impossible to obtain the data needed to properly evaluate the condition of the nation’s levees using these invasive methods. Therefore, there is a need for a rapid, proactive, non-destructive assessment procedure that can quickly and cost effectively gather continuous data, so that the most accurate performance evaluation can be made before defects in the levee lead to catastrophic failures. The second issue is related to a lack of funding to rehabilitate or update the currently deficient levees. The levees in the NLD are more than 55 years old on average and were originally designed to protect farmland from flooding; however, due to urban sprawl and changes in land use, over 14 million people now live or work behind these structures. Unfortunately, only 8% of these levees are found to be in acceptable condition, while about 69% are minimally acceptable, and 22% are rated as unacceptable. ASCE estimates more than $100 billion is needed to repair and rehabilitate the US levee system; however, only a small portion of that money ($415 million per year) is currently allocated by the federal government for flood control. Therefore, the available money must be used to repair the most critical levees first. Unfortunately, there is no procedure in place currently which can quantitatively determine which repairs or which levees are critical. Therefore, there is a need for a framework which can quantitatively assess the extent and severity of detected defects and their influence on performance. The goal of this research is to address both of these issues in a cost effective manner through the development of a rapid, non-destructive geophysical testing program. A series of geophysical field trials were completed to determine the most efficient methods and the best parameters for detecting various features or defects. A laboratory testing program were completed to determine the correlation between different soil types and resistivity values. The ability to quickly identify critical areas within a levee system so that they may be monitored or repaired is crucial if the levee system is to be improved with such limited funds.
Format:
PDF
Funding:
DTRT13-G-UTC50
Collection(s):
US Transportation Collection University Transportation Centers
Main Document Checksum:
[+]
urn:sha256:967d914c19bb6f6a6cceeaa313121261945ec67ea17edfb96df31f901bb6e4ba
Download URL:
https://rosap.ntl.bts.gov/view/dot/32818/dot_32818_DS1.pdf
File Type:

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