Pluvial flooding is caused by rainfall events that overwhelm drainage systems and do not allow excess water to be absorbed by soils or water infrastructure. This type of flooding occurs frequently in urban systems and leads to public inconveniences and infrastructure deterioration, which could cost more than fluvial flooding over time. Increased rainfall intensity, which is projected to increase with climate change, could result in increased pluvial flooding. This study aims to examine the vulnerability of pluvial flooding in Portland, OR (2010-2017) by incorporating an interdisciplinary framework that examines the physical and socioeconomic vulnerability of flooding through citizen-reported flooding data. We use a spatially dense network of 5-minute interval rainfall measurement to examine 3-day storm events associated with flooding reports to correlate storm size with the frequency of reports. Additionally, we use a Topographic Wetness Index (TWI) to identify the hotspots of pluvial flooding over space and characterize the sociodemographic and building characteristics of hotspots by performing a spatial analysis using census tract and tax lot level data. We investigate how individual neighborhood characteristics (i.e. ethnicity, education, gender, age, income) and building characteristics (i.e. building type, building age) contribute to reported flooding. This research seeks to identify where pluvial flooding occurs across the city, and how flood management planning can better address flood vulnerability through the biophysical and socioeconomic characteristics that exists amongst communities in Portland.

The development of a high-resolution coupled one-dimensional/two-dimensional hydrodynamic model of Charles City, Iowa is presented in this study as part of a larger Iowa Flood Center initiative to create a library of steady inundation maps for communities in Iowa which have a high risk of flooding. Channel geometry from bathymetric surveys and surface topography from LiDAR were combined to create the digital elevation model (DEM) used in numerical simulations. Coupled one- and two-dimensional models were used to simulate flood events; the river channel and structures were modeled one-dimensionally, and the floodplain was modeled two-dimensionally. Spatially distributed roughness parameters were estimated using the 2001 National Land Cover Dataset. Simulations were performed at a number of mesh resolutions, and the results were used to investigate the effectiveness of re-sampling simulation results using higher- resolution DEMs. The effect of removing buildings from the computational mesh was also investigated. During 2011, the stream channel geometry is being changed as part of a recreational park in downtown Charles City. After incorporating the planned changes to the stream channel, the model was used to create a library of steady inundation maps which are available on the Iowa Flood Center website.

Coastal areas are often important to economic, social, and environmental processes throughout the world. With changing climate and growing populations in these areas, coastal communities have become increasingly vulnerable to extreme flooding events, such as tsunami, storm surges, and flash floods. Within this new paradigm, there has been an effort to improve upon current methods of hazard assessment, particularly for tsunami. Recently, the American Society of Civil Engineers (ASCE) released the ASCE 7 Chapter 6 which was the world’s first standard, written in mandatory language, that addressed tsunami resilient design in a probabilistic manner for several of its prescriptions. While often the focus tends to be on mapping the hazards related to hydraulic loading conditions, post-tsunami field surveys from disaster-stricken coastal communities have also shown the importance of also considering the loads exerted by solid objects entrained within the inundating flows, commonly referred to as debris loading. Limited research has addressed debris hazard assessment in a comprehensive manner. Debris loading can be generally divided into two categories: impact and damming. Debris impact loads are caused by the rapid strike of solid objects against a structure. Debris damming loads are the result of the accumulation of debris at the face of or around a structure, causing thus an obstruction to the flow. The primary difference between these loads is the time period over which they act. The rapid loading due to debris impacts requires structural properties be considered in assessing the associated loads whereas debris damming loads are generally considered in a quasi-static manner. In assessing the hazard associated with both impact and damming loading conditions, methodologies must be developed to consider the likelihood of the load occurring and the magnitude of that load. The primary objective of this thesis was to develop a probabilistic framework for assessing debris hazards in extreme coastal flooding events. To achieve this objective, the components of the framework were split into three general categories: debris transport, debris damming, and debris impact. Several physical experimental studies were performed to address each of these components, representing the most comprehensive assessment of debris hazards in extreme flooding events to date. Debris transport was addressed to estimate the likelihood of debris loading occurring on a structure. The studies presented herein examine the different parameters that must be considered in assessing the motion of debris with the flow. The studies showed that the initial configuration of the debris and hydrodynamic conditions were critical in determining the motion of the debris. The stochastic properties of the debris motion were also assessed. It was shown that the lateral displacement of the debris could be approximated by a Gaussian distribution and the debris velocity by a Kumaraswamy (1980) distribution. The study of debris impact was further used to develop the current models used in estimating the impact force. The rigid body impact model was compared to models where the structural response was considered. The analysis showed that the effective stiffness model proposed by Haehnel and Daly (2004) was best suited to provide a conservative estimation of the impact force. Additionally, the impact geometry was taken into consideration examining the influence of various parameters on the impact force. Furthermore, debris damming was examined for the first time in transient loading conditions. This particular study examined the influence of the transient wave condition on the debris dam formation as well as the influence of different debris geometries. The influence of the debris dam geometry was correlated to increases in loading and overtopping conditions at structures. The assessment of debris hazards is critical in the development of accurate design conditions. The probabilistic framework presented within this thesis is expected to provide a basis for estimating debris hazards and inform future studies in the development of hazard assessment models.

It has been stressed within social sciences that risk management has focused too much on technical solutions and in order to decrease the risks also social factors have to be taken into account, namely the way people perceive risk. Risk perception is an important research field working on these issues. The aim of the study was in the light of the diverging views between the two paradigms to understand which of the psychometric or the cultural theory paradigm that can to a larger extent explain the flood risk perception of people living in the Tisza River basin. Furthermore the aim was to understand how the gap between experts’ and the public’s view on flood risk communication can be understood as well as how the risk communication could be improved. Data was collected through a survey and interviews. The results show that risk perception can partly be explained by either paradigm. To better understand people’s risk perception studies need to be more empirically based, not treat people’s perception as something too abstract and understand the interaction between individuals, society and the environment. The gap between the public’s and experts’ views is not as large as expected. In order to improve flood risk communication, decision makers need a better understanding of citizens’ perceptions and the motivation to include public perception in flood risk management need to be based on the view that the public could have an important input into risk management.

A regional synthesis of paleoflood chronologies on rivers in Arizona and southern Utah reveals that the largest floods over the last 5000 years cluster into distinct time periods that are related to regional and global climatic fluctuations. The fine-grained flood deposits used to reconstruct these flood histories selectively preserve evidence of only the largest events. Large floods were frequent on rivers throughout the region from 4.8-3.6 ka (¹⁴C yrs). In contrast, the period from 3.4-2.2 ka is marked by a significant decrease in the number of large floods on virtually all of the rivers. The frequency of large floods increased after about 2.2 ka, with particularly prominent peaks around 1 ka and after 500 yrs BP, separated by a sharp decrease between 600 and 800 yrs BP. The storms that generate large floods (≥ 10-year) in this region fall into three general categories: 1) winter North Pacific extratropical storms, 2) late-summer and fall storms that draw on moisture from recurved Pacific tropical cyclones, and 3) summer storms, mainly convective thunderstorms. Winter storms and tropical cyclones are associated with the very largest floods on the rivers with paleoflood records, and are the most probable causes of the late-Holocene paleofloods. Floods from both winter storms and tropical cyclones occur when deep mid-latitude troughs steer storm systems into the region. Composite anomaly maps of daily 700-mb heights and monthly sea-level pressure indicate that the winter floods are associated with a low-pressure anomaly off the California coast and a high-pressure anomaly over the Aleutians or Gulf of Alaska. Shifts in the locations of the low- and high-pressure anomalies over the North Pacific appear to control which subregions of the southwestern U.S. experience floods. Composite 700-mb anomalies during tropical cyclone floods show a similar pattern, with a variation to a blocking high-pressure anomaly in the central North Pacific and a low-pressure anomaly over the western U.S. There is a strong connection between the negative phase of the Southern Oscillation Index and the large floods associated with winter storms and tropical cyclones. Over the last 5000 years, the episodes of more frequent large floods coincide with cool, wet, neoglacial periods. Warm periods are times of dramatic decreases in the number of paleofloods. Although the floods record individual extreme storms, they cluster in times of generally moister conditions in the region. A clear positive relationship exists between floods and low-frequency variations in El Niño over the last 1000 years. Warm coastal sea-surface temperatures indicative of El Niño-like conditions are associated with more frequent large floods over at least the last 2000 years. The paleoflood records demonstrate centennial-scale variations in the conditions conducive to the occurrence of large floods in this region.

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This study uses multiple isotopic (2H, 18O, 13C, 15NNO3, 18ONO3, 87Sr/86Sr) and age tracers (3H, 14C, CFCs), in conjunction with elemental chemistry, to address the following research question: How have present day anthropogenic activities (i.e. surface water irrigation and fertilizer application) and past climatic events (i.e. cataclysmic flooding from glacial Lake Missoula and other modes of discharge from Cordilleran Ice Sheet) impacted the hydrology and geochemistry of the Columbia River Basalt Aquifers (CRBAs) in central Washington? Large-scale irrigated agriculture over the past ~60 years has resulted in the transport of high NO3- irrigation waters moving downward in the oxic CRBAs at rates of several meters per decade with a lack of denitrification. Deeper pristine regional groundwater in the CRBAs is Late Pleistocene in age and likely remnant Cordilleran Ice Sheet-related recharge waters (i.e. glacial Lake Missoula floodwaters).

Tne main purpose of this paper was to apply statistical methods for extreme events and to estimate probabilities of exceedance of the highest water level recorded and return period of a very large inundated area. Since Nemunas River water levels follow each other time-wise, they were examined in time series context.

In unsteady flows, dune dimensions may vary considerably from fully-developed dimensions produced from a flat bed under a steady and uniform flow. Specifically, dune height and length are observed to lag discharge when the flow is non-steady, resulting in dimensions that are out of phase with the prevailing flow. This research attempts to provide some insight into the behaviour of dunes when the flow is suddenly changed, as well as the time-scale of the related dune changes. Nineteen experimental runs were carried out in the 21-m long, 0.76-m wide Sediment Transport Flume at Queen’s University. In ten of these runs the flow depth, h, was suddenly increased (h2/h1 > 1) and in nine runs the flow depth was suddenly decreased (h2/h1 < 1). In all runs, the slope of free surface was kept equal to the slope of the bed such that the change in flow rate is represented by the change in the flow depth. Seven ratios of the two flow depths, h2/h1 (varying between 0.49 and 2.29), were performed for three slopes (S = 1/792, 1/534, 1/341). The bed material was a coarse, poorly-graded silica sand (D50 = 1.0 mm). Longitudinal bed profiles were taken along the centreline of the flume approximately every 6–8 minutes to determine the transient dune dimensions and the time at which the dunes acquired their new equilibrium dimensions. This time is termed the duration of dune development, Td. Through dimensional and physical considerations, Bielenberg (2006) established that the dimensionless counterpart of Td should be a function of the material number, relative flow depth, relative flow intensity, and ratio of the flow depths h2/h1. The present experiments were carried out to investigate the influence of the relative flow intensity and h2/h1 on the duration of dune development. Results indicate that equilibrium dune dimensions do not depend on the initial shape of the bed. After the period Td, the dunes tend to be similar to those produced from a flat bed. It is found that Td is strongly dependent on h2/h1, and weakly dependent on the flow intensity. All other determining variables remaining the same, Td decreases with increasing values of flow intensity. Semi-empirical relations for the dimensionless duration of dune development are presented. / Thesis (Master, Civil Engineering) -- Queen's University, 2007-09-24 09:45:13.624

No description available.