Levees and levee evaluation The Dutch and US practice compared Msc. Thesis Fugro Ingenieursbureau BV Delft University of Technology P.R.M. Ammerlaan 2007 Picture front page: Levees along the San Joaquin River California at Reclamation District 17; 01-29-2007 P.R.M. Ammerlaan ii Levees and levee evaluation The Dutch and US practice compared Msc. Thesis P.R.M. Ammerlaan Student number: 1017446 August 2007 Committee: Prof. drs. ir. J.K. Vrijling (TU Delft, Hydraulic Engineering dep.) Ir. M.T. van der Meer (Fugro Ingenieursbureau BV / TU Delft, Geo Engineering dep.) Dr. ir. P.H.A.J.M. van Gelder (TU Delft, Hydraulic Engineering dep.) Ir. J. Nijman (Fugro Ingenieursbureau BV) Delft University of Technology Fugro Ingenieursbureau BV Delft, the Netherlands Leidschendam/Nieuwegein, the Netherlands Preface This report is the final version of my master thesis for Hydraulic Engineering at Delft University of Technology with the title: “Levees and levee evaluation, the Dutch and US practice compared”. An immediate question that will rise is probably: “What is a levee?” In the Netherlands we are familiar with the word dike as a translation of the Dutch ‘dijk’. The word dike is sometimes used in the US, but in California as well as Louisiana levees is the preferred word, derived from the French word levée and introduced in New Orleans by the French in the 17 th century. I will therefore only speak of levees in this report and will not use the word dike. This levee subject was suggested to me by Fugro Ingenieursbureau BV in the Netherlands and they supported me during this thesis and offered me the chance to learn about levees and levee evaluation in the US. I have spent 9 weeks in the Fugro West inc. office in Oakland, California and have been to Houston, Baton Rouge and New Orleans as well to talk about and see levees. The final result of the past 10 months is a report which is not only theoretical (chapter 7 is a theoretical/empirical study of the mechanism piping), but is also a very broad introduction to levees and levee evaluation in the Netherlands as well as in the US, especially California and gives an overview of the differences and similarities. I hope that for that reason people who are interested in an exchange of knowledge between the US and the Dutch levees will use my report as a first start. The more theoretical part of this thesis is hopefully triggering people to study the mechanism piping more closely and critically look at the current design and evaluation criteria in the Netherlands as well as the USA. I would like to thank the people who supported me during my thesis: Professor Han Vrijling and Pieter van Gelder from my university for their comments and support, Martin van der Meer from Fugro for giving directions and critical comments and Job Nijman from Fugro for his support before and during my visit to the US. Patricia Ammerlaan August, 2007 v Summary The Central Valley and Sacramento-San Joaquin Delta in California are identified as extremely vulnerable to major flood disasters of the size as the 2005 New Orleans flood. With its low-lying polders and rivers flowing into a delta this part of California shows some remarkable similarities with the Netherlands. The first goal of this report was to identify the vulnerabilities of the Central Valley and Delta flood protection system and to compare them to the Dutch water defense system. A second goal was then to focus on important weaknesses or differences, try to find out their background and/or come up with recommendations on how to improve them. This Central Valley receives runoff from the Sierra Nevada Mountains, which is drained mainly in the Sacramento River and the San Joaquin River, passing densely populated areas with the cities Stockton and Sacramento. These rivers drain in the Delta, which is the center of a large north- south water delivery system More than 22 million people (2/3 of the Californian population) partly rely on drinking water and irrigation water from the Delta. More than 3,800 km of levees protect the Central Valley and Delta, against floods. The Central Valley and Delta levees are supposed to provide a 100-year flood protection and in current evaluation program this is raised to a 200-year level. There is no federal flood protection standard. This 100-year protection is a requirement from the Federal Emergency Management Agency (FEMA), who carries out the National Flood Insurance Program (NFIP). The River levees in the Central Valley are subject to seasonal floods in spring, when melting snow in the Sierra Nevada increases runoff, while the Delta levees hold back water the entire year. Although the Delta is situated in a relatively protected area, sheltered from the ocean, tidal influences and wind wave actions from the San Francisco Bay can still harm the area. From none of the 162 delta levee breaches of last century an indication was found that it was caused by a seismic event. However, there are people that believe that one of the most important threats to the delta is an earthquake, especially in combination with high water levels. If the levees fail, or maybe better: when the levees fail in the Delta and/or along the rivers, the consequences are enormous. River levee failures will mainly be destructive to urban areas. Sacramento alone has already more than 450,000 inhabitants. When levees in the Delta fail, salt water will be drawn into the area. Not only people, species and infrastructure within the Delta will be harmed by the salt water, but also the people that rely on drinking and irrigation water from the Delta. The levees are degrading from erosion and subsidence. The changing climate and growing population will ask more from those already vulnerable levees. Plans are developed to improve the flood protection in the Central Valley and Delta. Most of these plans are now gathered under “FloodSAFE California”, an initiative of the DWR (Department of Water Resources) of California. Evaluation of the urban levees is a currently running initiative financed with state bond debts. 25% of the Netherlands is situated below mean sea level. And in total 60% of the Dutch land area would be flooded daily without levees, dunes and barriers. Most of the economic activity and urbanization is in this part of the country. The Dutch water defenses are divided in primary water defenses and regional water defenses. The water levels against those primary water defenses, protecting 53 dike ring areas, are influenced by the tide, waves, storm surges and/or river discharges from the North Sea and the Rivers Meuse and Rhine. They have to be able to resist a water level with an occurrence of 1:10,000 per year to 1:1,250 per year, depending on economic vii consequences within the dike ring area. Regional water defenses lie within these dike ring areas and often encircle polders with a regulated water level. Water levels at the regional levees are kept relatively constant. Large infrastructure works have been built to protect the Dutch polders. Storm surge barriers as in the Western Scheldt and the Nieuwe Waterweg are examples of this. Another example is the closure dam between the Wadden Sea and Lake IJssel, which was built to protect people living along the former Zuyder Sea against storm surges. But the climate is changing and floods seem to occur more often than they did before. Main drivers of an increased flood risk are the changing climate, which leads to sea level rise, increasing river discharges and increasing wet and dry periods. As in the rest of the world population growth and economic growth make that the damage floods cause is increasing. One of the initiatives to deal with flood risks in the future is the FLORIS project, Flood Risks and Safety in the Netherlands (or in Dutch: VNK). It intends to get more insight in the chances of flooding and the consequences of a flood. Another initiative is the Room for the River project, established after the 1993 and 1995 extreme river water levels; goal is to find new solutions for a better protection against the water from the large rivers. In the Flood Protection Act is stated that each 5 years levee authorities have to report on the conditions of the primary water defenses following the prescriptions from the ministry, the ‘Voorschift toetsen op veiligheid’ (VTV). There is no legislation (yet) on the regional water defenses. How a levee is evaluated in the Netherlands depends on the expected failure mechanisms in an area. Macro instability of the levee, piping, overtopping and micro instability are the main mechanisms considered in a levee evaluation. Other mechanisms, which are evaluated depending on the local levee conditions, are instability of the foreland, instability of the revetment, instability by infiltration and erosion at overtopping, heave and horizontal sliding at foundation. For each of the mechanisms a process from simple to advanced is used, based on a ground model and evaluation methods. From the basic soil research that is prescribed, borings combined with soundings and lab tests, a ground model is developed and the levee is divided into sections with equal characteristics. When a levee section is expected to be vulnerable to a certain failure mechanism with a simple evaluation, more extensive soil research on the specific location and more detailed or advanced models are used. When after several steps a levee still seems vulnerable, that levee section is rejected. Improvements are necessary. The levee is then evaluated under normative conditions.