Levee crest elevation profiles derived from airborne lidar-based high resolution digital elevation models in south Louisiana

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Abstract

This study explores the feasibility of using airborne lidar surveys to construct high-resolution digital elevation models (DEMs) and develop an automated procedure to extract levee longitudinal elevation profiles for both federal levees in Atchafalaya Basin and local levees in Lafourche Parish, south Lousiana. This approach can successfully accommodate a high degree of levee sinuosity and abrupt changes in levee orientation (direction) in planar coordinates, variations in levee geometries, and differing DEM resolutions. The federal levees investigated in Atchafalaya Basin have crest elevations between 5.3 and 12 m while the local counterparts in Lafourche Parish are between 0.76 and 2.3 m. The vertical uncertainty in the elevation data is considered when assessing federal crest elevation against the U.S. Army Corps of Engineers minimum height requirements to withstand the 100-year flood. Only approximately 5% of the crest points of the two federal levees investigated in the Atchafalaya Basin region met this requirement.

Introduction

Flood protection in south Louisiana is largely dependent on earthen levees. More than 2800 miles of levees (4500 km) protect over 19,000 square miles (49,210 square kilometers) of land in Louisiana (ASCE, 2012). The levees are managed by 35 levee districts, with more than half located in southern Louisiana. The majority of levees along the Mississippi River and around the Atchafalaya Basin are federal levees primarily designed for riverine flood control under the jurisdiction of the U.S. Army Corps of Engineers (USACE). Local levees are designed for protection from backwater flooding caused by riverine, storm-surge, or precipitation events and are maintained by the levee districts (Fig. 1). The minimum federal levee design standards are specified in the USACE 44 CFR 65.10 and EM 1110-2-1913 (USACE, 2000) documents. These standards specify the material of construction and compaction levels according to the levee type or location, maximum slope angle, minimum crown width, and minimum height of at least 3 ft (0.9 m) above the 100-year flood level.

Levees were formed naturally by the Mississippi Rivers’s fluvial processes and were later built up by the first settlers in this area in the beginning of the 18th century. Soon thereafter, levee building and maintenance were a mandatory requirement in order to maintain land ownership (NHRAIC, 1992). Piecemeal levee systems were developed and maintained by state-created levee districts and boards through the mid-19th century. The Civil War disrupted levee system maintenance and development through the late 1870s (Davis, 2000). Major floods during this period led to the formation of the Mississippi River Commission in 1879 to provide federal oversight of navigation and flood control on the Mississippi River. The increasing population and new settlements in the flood plains intensified the risk to property and life, and several devastating floods towards the end of the 19th century called for the federal government to take on the responsibility for flood mitigation. The damage caused by the Great Flood of 1927 led to the passage of the 1928 Flood Control Act, fostering the enlargement of existing levees and the construction of new ones (NHRAIC, 1992, Tobin, 1995). After Hurricane Betsy in 1968, the U.S. Congress directed and authorized the USACE to provide hurricane protection projects and in 1968 the National Flood Insurance Program (NFIP) was established. The Flood Disaster Protection Act of 1973 called for new expansions both vertically and horizontally of the existing levees. In 1986 USACE developed the standards of minimum federal levee design 44 CFR 65.10, subsequently updated in 2000 by USACE EM 1110-2-1913 (Fig. 2). The Federal Emergency Management Agency (FEMA) coastal NFIP levee system evaluation requirements state that the levee should provide protection against the base flood level, defined as a flood that has a one-percent chance of being equaled or exceeded in any given year (also referred to as the 100-year flood; USACE, 2010).

In comparison to federal levees, local levees are much smaller, they do not have an established design standard, and are managed by approximately 35 local levee districts in Louisiana. Local levees were first developed by European immigrants to provide protection from riverine flooding and improve agricultural drainage as settlement expanded along the natural levee ridges. A typical delta distributary is often bounded by large riverine flood protection levees adjacent to the channel and by smaller local levees located outside the delta, where arable lands grade to swamps and marsh. These lands were originally at swamp or marsh elevation when constructed. These crude early levees were insufficient to provide adequate riverine flooding protection, eventually leading to their enlargement by adding spoil material. This evolution was parallel with the development of the federal levees along the Mississippi River that ultimately interrupted the sediment nourishment of the deltaic areas that had naturally occurred during periodic floods. Localized subsidence increased from cessation of natural land aggrading floods and accelerated soil oxidation, increasing flooding risks. As a consequence, subsidence started to overtake sediment accretion rates and in turn necessitated the introduction of water pumps to decrease the water levels. Meanwhile, in some cases, the stability of the protective local levees on the banks of the channels became compromised due to erosion, sliding of the stability berm, steep sides, and insufficient levee crest elevation (Fig. 3).

Earthen levees deteriorate over time, with erosion, scouring, compaction, and subsidence reducing their mass or height. Overtopping of levees, which occurs when high water levels exceed the elevation of the levee crest, is one of the primary modes of levee failure. Other types of failure mechanisms in earthen levees include seepage, erosion, slump/spread, bearing (loss of soil strength), and sliding (Moss and Eller, 2007). Areas along levees where crest heights differ or where there is an opening in a levee are typical locations for seepage, overtopping, and erosion to occur (Moss and Eller, 2007). In south Louisiana, high rates of subsidence can cause the levee crest elevations to continually diminish unless new material is added to maintain the height of the levee structure. South Louisiana has the highest rates of relative sea level rise in the United States due to land subsidence (Zervas, 2009). Because coastal flooding will become more frequent as sea level rises (Bindoff et al., 2007, Rahmstorf, 2007), the risk of levee failure will become an even greater threat in the future. Therefore, systematic, comprehensive monitoring of levees in south Louisiana is needed to identify degraded levee segments before a disaster such as levee overtopping or breaching occurs.

Generally, the use of traditional manual surveying methods to map levees is a costly and time consuming process that typically produces cross-levee profiles every few hundred meters, at best. The purpose of our paper is to describe and test methods for extracting levee crest elevations in an efficient, comprehensive manner using high resolution lidar. We present methods to automate the extraction of levee crest heights at 1-m intervals using commonly available GIS software, or R open-source software. In addition, the vertical uncertainty in the elevation data and its effect on the resultant estimate of levee crest heights is addressed in an assessment of whether the federal levees in our study meet the USACE minimum height design criteria.

The 2012 Coastal Master Plan for Louisiana identified the need for flood risk reduction and the promotion of new land building or sustaining existing land as major decision drivers. These drivers are prominently supported by citizens and local leaders (CPRA, 2012). Current and accurate elevation information is crucial to adequately develop landscape models to help advance the main objectives of the 2012 Coastal Master Plan, particularly in southern Louisiana where elevation data is outdated (the current regional digital elevation model (DEM) is derived from 2001 to 2002 lidar data) and incomplete. Since 2010 there has been a concerted effort by federal and state government agencies and other partners to acquire high resolution lidar data in the coastal zone of southern Louisiana (Fig. 4).

Section snippets

Study areas

The study area covers over 30 linear kilometers of levees in southern Louisiana; two federal levees in the Atchafalaya Basin region, and two local levees in Lafourche Parish. The lidar data for Atchafalaya basin were collected in December 2010 when water levels were low, covered 981 square miles (2540.78 square kilometers), and used the Optech’s Gemini ALTM 213 airborne lidar sensor with a nominal point spacing of 1 m. These parameters supported a nominal swath width of 930 m and an average point

Methodology

Because the levee system in Lafourche Parish is so extensive (approximately 340 linear km of levees), hand digitizing the levee crest and margins was deemed to be too labor-intensive. Levee slope analysis techniques developed for California levees (Casas et al., 2012) were tested, but were not successful in defining the levee margins or crown due to the very small size and low topographic relief of the local levees. Therefore, techniques for extracting somewhat similar geomorphic features from

Comparison of least cost path and matched points transect methods

The matched points transect method was selected as the best among the three methods developed in R, because it is the most parsimonious and straightforward and does not necessitate any post-processing of the crest result. Besides, this method generates the levee margins as well that not need to be post-processed unless the levee morphology is very complex and changes along the levee. The matched points transect method and the least cost path results were compared only for the longest federal

Conclusions

Southern Louisiana has a long history of flood control through levees. The federal levees evolved from the flood control levees along Mississippi River and Atchafalaya Basin, have a strict standard of construction, and are under the jurisdiction of the USACE. In comparison, the local levee system is generally the result of land drainage for agriculture purposes, is much lower in height, does not have a standard of construction, can have very sharp changes in direction and is maintained by the

Disclaimer

This draft manuscript is distributed solely for purposes of scientific peer review. Its content is deliberative and predecisional, so it must not be disclosed or released by reviewers. Because the manuscript has not yet been approved for publication by the U.S. Geological Survey (USGS), it does not represent any official USGS finding or policy.

Acknowledgments

We thank Dwayne Bourgeois, Executive Director, North Lafourche Conservation Levee and Drainage District, and Maurice Wolcott, Coastal GIS Specialist, Louisiana Sea Grant and Louisiana State University for their assistance in explaining the history and development of the local levee system in southern Louisiana. The funding of this project was provided by the Coastal and Marine Geology Program, U.S. Geological Survey through the Northern Gulf of Mexico project. Any use of trade, product, or firm

References (29)

  • Environmental Systems Research Institute (ESRI), 2013. ArcGIS 10.1....
  • D.B. Gesch

    Analysis of lidar elevation data for improved identification and delineation of lands vulnerable to sea-level rise

    J. Coast. Res., Special Issue

    (2009)
  • Hapke, C., Reid, D., Borrelli, M., 2008. The National Assessment of Shoreline Change: A GIS Compilation of Vector Cliff...
  • Hijmans, R.J., van Etten, J., 2012. Raster: Geographic analysis and modeling with raster data. R package version...
  • Cited by (0)

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