Includes bibliographical references (p. 227-244).

Thesis--Wisconsin. / Includes bibliographical references (leaves 90-91).

No description available.

The model choice problem in Hydrology is illustrated by means of the optimum levee design for flat rivers along a confluence reach. Special attention is given to the selection of a probability distribution for the joint flood stages. The optimality criterion used is the minimization of construction plus expected flood damage costs. The main assumption in the mathematical model is that the levee profile is uniquely determined as a function of the levee heights at the extremes of the reach; thus the problem is reduced to the determination of the optimum pair of extreme levee heights. The selection of a probability distribution of flood stages, from a set of distributions estimated from the partial duration series, is performed using either one of two selection procedures: likelihood of the Chi -square statistic and sample likelihoods. A composite distribution, taking into account the model uncertainty, is also derived. The methodology presented is applied to the remodeling of the levee on the west bank of the Zagyva River, in Hungary. A sensitivity analysis is performed, using the best ranking distributions according to the two model choice procedures. The composite distribution appears to offer a reasonable choice.

An important fraction of the reservoirs in the Outer Continental Shelf of the Gulf of Mexico is comprised of thin-bedded deposits from channel-levee systems. These reservoirs are particularly difficult to describe. Not only is their architecture complex but the quality of the reservoir is determined by connection and length of beds below the resolution of usual reflection data. Improved characterization is needed to improve development and production of these reservoirs. This study presents an integrated approach to build a geologically consistent reservoir model, based on the 8 sand reservoir in Northern Green Canyon block 18. The underlying idea of the construction of this model is that reservoir quality is influenced more by the internal architecture than by the statistical values of petrophysical parameters. Seismic interpretation and attribute extraction provided the reservoir geometry and stratigraphy. The structural framework and the limits of the reservoir have been determined, showing the preeminent role of salt and faults in the constitution of this reservoir. Seismic attributes are calibrated to extract areal information on reservoir architecture. Gross thickness and net thickness maps have been estimated using geostatistical methods. Lateral variations in the quality of the 8 sand and the definition zones with different average properties were inferred from geostatistical results. Lithofacies characterization from core showed that 3 facies could be used to describe the internal variability. The fine-scale heterogeneity is described in each zone from vertical facies distribution determined from wells. A truncated Gaussian sequential simulation was performed to reflect both the regional trend and the internal variability on a 150*150*1 ft grid. The major contribution of this work is to show the efficiency of this approach to describe complex reservoirs where the impact of internal variability is a major control of flow efficiency. This is especially valuable when the well information is scarce or not uniformly distributed. This model will be used for flow simulation and sensitivity analysis to improve the field description.

Deep-marine levees are areally extensive features that border submarine channel systems. Compared to the adjacent channel, where episodes of erosion and bypass are commonplace, levees are mostly depositional features that experience little erosion, and therefore high preservation potential of individual beds, and presumably provide a nearly continuous depositional record of transport events down deep-marine slopes. Nevertheless, despite their size, volumetric prominence, and interpretive significance, deep-marine levees have received much less research attention compared to the adjacent channels. Accordingly, the spatial and temporal evolution of levee stratigraphy is much less well understood, in part because of the typically recessive nature of levee deposits exposed in outcrop in the ancient sedimentary record, and insufficient seismic resolution seismic in the modern. Also, although modern deep-marine levees have been shown to sequester a large proportion of the world’s total buried organic carbon, few studies have attempted to assess carbon deposition and preservation in ancient deep-marine levee deposits. In the Isaac Formation of the Windermere Supergroup (Neoproterozoic) of east-central British Columbia, Canada, well-exposed levee deposits display a systematic organization on several dimensional scales. Levee packages (decameter-scale) are interpreted to be due to cyclic changes in the granulometric makeup of sediment being supplied to the system, whereas bedsets (centimeter- to meter-scale) are interpreted to represent systematic and recurring pulses or surges during a single flow event. Furthermore, physical and geochemical characterization of levee strata at Castle Creek has shown that the unique depositional processes in levees can result in the concentration and enrichment of sedimentary marine organic matter (OM), which occurs mostly in banded, mud-rich sandstones deposited under oxic conditions. Organic carbon occurs primarily as nano-scale coatings on clay particles and uncommon sand-sized organomineralic aggregates and discrete sand-sized amorphous grains. The distribution of this OM in levee strata is controlled by a combination of primary productivity, sea level, and rates of continental runoff and detrital terrigenous influx, which collectively are principally controlled by climate. Understanding the stacking patterns, geochemistry, and organic content of ancient levee deposits is important for assessing sedimentation patterns, depositional processes, event frequency and magnitude, paleoenvironmental conditions, and the evolution of ancient ocean and climate systems.

The wetlands of Louisiana have provided protection against floods and storms for thousands of years. With the construction of the Mississippi River levees and increased urbanization the wetlands are quickly disappearing, thus leaving the area vulnerable to hurricane storm surge. Since Hurricane Katrina, levees have been showcased as the only way of fully protecting southeast Louisiana from floods and storms; however, this is also being accompanied by a push for more funding for coastal restoration. There is evidence that hurricane protection levees and coastal restoration are incompatible. This research examines the implications of levees on the wetlands both directly and indirectly. Furthermore, a survey was conducted to discover public perception about the impacts of levees in southeast Louisiana by residents most as risk for flooding from hurricane storm surge.

A new method for assessing the potential for unsatisfactory levee performance due to underseepage is presented. Specifically, the method assesses the potential for the initiation of piping (the internal backward erosion of the foundation or embankment caused by seepage). Current assessment methods consist of deterministic seepage analyses and simplified reliability methods. Deterministic methods produce either a maximum hydraulic exit gradient or a Factor of Safety against piping but they do not account for high levels of uncertainty in soil properties and subsurface geometry that are inherent to many levee analyses. The most common simplified reliability approaches that are currently being used to analyze levees with regard to underseepage apply the First Order Second Moment (FOSM) Taylor Series method using the US Army Corps of Engineers "Blanket Theory" equation as the performance function. These methods take into account the uncertainty of the soil properties but are limited to simplified subsurface geometries and often do not model the actual mechanism responsible for levee failure due to underseepage piping. The proposed new method uses a Monte Carlo simulation to calculate the probability of unsatisfactory levee profile performance and can take into account complexities in subsurface geometry that cannot be assessed using the simplified reliability methods. The relationships between uncertainty of the soil parameters, the subsurface geometry, and the Factor of Safety against piping are defined through parametric variation analyses of a finite-element seepage model. The results of the parametric analyses are used to develop a series of equations that define the relationship between the various input parameters and the factor of safety. Using these equations, probability density functions for the various input parameters, and the computer program @Risk which interfaces with Excel, a Monte Carlo analysis is performed to calculate the probability of unsatisfactory performance which represents the probability of initiating erosion given a river flood level. The results of the analysis represent a single node of the event tree. In order to assess failure potential, other points in the event tree will need to be assessed with calculations or judgment since it is only the first phase that is currently considered to be in the process of piping. The new method is demonstrated using actual data of levee profiles from the Natomas Basin in Sacramento, California as a case study. The case study highlights the benefits of reliability-based analyses over the Factor of Safety and demonstrates the importance of subsurface geometry in reliability calculations.

This study combined flood-frequency analysis, 1-D (one-dimensional) hydraulic modeling using HEC-RAS, and flood-loss modeling using FEMA's Hazus-MH (Hazards U.S. Multi-Hazard) in order to: 1) quantify how different flood-frequency methodologies affect flood-risk assessments, and 2) quantify the impacts of different floodplain-management scenarios along the Middle Mississippi River (MMR). The nine scenarios tested here included various combinations of flood-frequency methodology, buyouts, and levee configurations. The levee configurations analyzed included: 1) current levee configuration, 2) no levees, 3) a 1500 m levee setback, 4) a 1000 m levee setback, and 5) a customized levee setback designed to maximize protection around existing infrastructure. Two study reaches were chosen: (1) an Urban Study Reach within St. Clair and northern Monroe Counties, IL, with levees designed to withstand the 500-year flood and (2) an Agricultural Study Reach within Union and Jackson Counties, IL, with <100-year levees. A flood-frequency analysis was completed for the St. Louis, MO gauging station, and detailed building inventories were used to estimate flood losses on a structure-by-structure basis (Hazus-MH UDF analysis) for an array of floods ranging from the 2- to the 500-year events. These flood-loss estimates were combined with a stochastic levee-failure model. Finally, estimated flood damages from Hazus-MH were integrated across the full range of flood recurrences in order to calculate expected annual damage (EAD). This study's flood-frequency analysis and corresponding flood-loss assessment demonstrate how differences in flood-frequency methodology can significantly impact flood-risk assessments. EAD based on the UMRSFFS (Upper Mississippi River System Flow Frequency Study) flood frequencies was 68% ($45.4 million) lower than EAD based on this study's flood frequencies. This decrease in EAD demonstrates that the UMRSFFS flood frequencies and corresponding stages may significantly underestimate flood risk within the Urban Study Reach. The 100-year discharge in the UMRSFFS appears to be underestimated by an estimated 17% (187,000 cfs), resulting in a 10% (1.6 m) underestimation of the 100-year flood level. Given the magnitude of the EAD, discharge, and stage differences documented here, a reanalysis of the MMR flood frequencies, flood profiles, and flood maps should be considered. The hydraulic modeling completed here showed that levee setbacks and levee removal successfully reduce stages for all recurrence intervals. For the 100-year flood, average reductions ranged from 0.20 m for a 1000 m levee setback to 1.61 m with levees removed. In general, stage reductions increased with increasing discharge and with increasing setback distance. The flood-level reductions are attributed to increased floodwater storage and conveyance across the reconnected floodplain. Compared to the current conditions, the levee setback and levee removal scenarios tested here reduced flood losses for large, infrequent flooding events but increased flood losses for smaller, more frequent flood events. When combined with buyouts of unprotected structures, levee setbacks reduced flood losses for all recurrence intervals. The 1000 m and 1500 m levee setbacks required buyouts in order to reduce EAD; however, a levee setback carefully planned around existing high-value structures reduced EAD with or without buyouts. The planned levee setback configuration combined with buyouts resulted in the largest decreases in EAD: a $16.8 million (55%) decrease in the Urban Study Reach and an $8.3 million (93%) decrease in the Agricultural Study Reach. Overall, this project showed that levee setbacks in combination with buyouts are an economically viable approach for flood-risk reduction along the study reaches and likely elsewhere where levees are widely employed for flood control. Designing a levee setback around existing high-value infrastructure can maximize the benefit of the setback while simultaneously minimizing the costs. Potentially, this type of planned levee configuration could be used as a template for the replacement of aging or failing levee systems.

This study utilized a new database of levee failures along 685 km of the Middle and Lower Mississippi River from St. Louis, MO to Memphis, TN during the past 120 years. The goals of this investigation were to: 1) identify the relative importance of geologic and geomorphic factors that have led to levee failures through the past century along the Mississippi River and 2) measure levee crest elevations to determine if they have increased or decreased between 1998 and 2007 and if they are built to the proper design grade elevation. Logistic regression analysis was utilized to examine selected site characteristics at each levee failure location. These site characteristics (levee failure parameters) included: 1) levee underlain by previous channel fill, 2) presence/absence of borrow pit, 3) location of failure on a meander bend, 4) width of channel, 5) width of floodway, 6) constriction-over-time factor, 7) land-cover type, 8) width of vegetative buffer, 9) sinuosity of channel, 10) intensity of dredging, and 11) presence/absence of bank revetment. Each of these parameters was evaluated using geologic maps, soil survey data, Digital Elevation Models (DEMs), historic river maps, and dredging reports (Winkley, 1977; Pinter et al., 2004). Two models were created for each river reach. The first model for both reaches used a 95% significance threshold, while the second model for the MMR used a 80% significance threshold, and the second model for the LMR used a 90% significance threshold. The first model for the Middle Mississippi River (MMR) identified only the presence/absence of channel fills to predict levee failure as significant, had an R² value of 0.178, a p-value of 0.002, and a percentage accuracy of 68.6%. The second model for the MMR identified the following variables as significant: presence/absence of channel fills to predict levee failure, location of failure on a meander bend, channel width, land-cover type, and intensity of dredging. This model had an R2 value of 0.408, p-value of 0.002, and a percentage accuracy of 74.3%. The 95% model for the Lower Mississippi River (LMR) identified location of failure on a meander bend, land-cover type, constriction-over-time factor, and sinuosity of the channel as significant. This model had an R2 value of 0.326, p-value of 0.003, and a percentage accuracy of 69.5%. The 90% LMR model identified the following variables as significant: the presence/absence of borrow pits, location of failure on meander bend, channel width, land-cover type, constriction-over-time factor, vegetative buffer width, channel sinuosity, and presence/absence of bank revetment. This model had an R2 value of 0.385, p-value of 0.006, and a percentage accuracy of 72.0%. The MMR and LMR models with the 95% significance threshold had no predictors in common because of differences between the two river reaches or possibly because of the small sample size. However, the expanded MMR and LMR models shared three predictors (i.e., meander location, channel width, and land cover type). The second portion of this project used post-processed dual-frequency GPS surveying to measure levee elevations between St. Louis, MO and Cairo, IL. These elevations were compared to the 50-year design flood grade elevations and to a 1998 DEM to identify areas of levee heightening, levee degradation and/or subsidence, and locations of past levee crevasses. This surveying revealed areas that, between 1998 and 2007, were raised up to ~1.5 meters and other areas that degraded or subsided up to ~1.0 meter. Also, the locations of five recent levee crevasses were investigated, showing local increases or decreases at those points. The importance of levee road construction type was identified through many sharp increases or decreases at the transition between road types. Overall, this project showed promising implications for the determination of levee failure susceptibility and proper levee elevation heights using logistic regression analysis and kinematic GPS surveying. The logistic regression models predicted the potential for levee failure based on local site characteristics of levees between St. Louis, MO and Memphis, TN. The high-precision kinematic GPS surveying illustrated levee elevations along the MMR to a high degree of accuracy, allowing for the rapid and efficient identification of areas that do not correspond to the proper design flood grade elevation.