R-3 Repository :: Browsing by Author "Bedient, Philip B"

Browsing by Author "Bedient, Philip B"

Now showing 1 - 7 of 7

Assessing Land Use Change and Subsidence Impact on Inland Flooding
(2022-04-08) Bahnick, Raychel; Bedient, Philip B
The greater Houston Area has been exposed to tremendous flooding in recent history (e.g., Hurricane Harvey (2017), Tax Day Flood (2016), Memorial Day Flood (2015)). The destruction and economic loss associated with these major storms highlights the flooding challenges the region faces. These consequences can be further exacerbated by increased land subsidence and urbanization. As watersheds urbanize, the imperviousness increases the runoff volume and peak discharge. There has been limited research on how land subsidence impacts inland flooding at a watershed scale. The goal of the study is to provide decisionmakers with a greater understanding of how the Panther Branch watershed reacts to human induced subsidence and land use change to better inform policy to protect residents in The Woodlands, TX from flooding in the future. This is achieved using remote sensing techniques of local GPS monitoring stations and LiDAR digital elevation models (DEMs) to analyze land deformation due to subsidence. A two-dimensional hydrodynamic model of a projected urbanized watershed was created and calibrated to historical storms. Cumulative land subsidence is highly correlated with past population growth in The Woodlands. Subsidence was linearly extrapolated about 50 years into the future. This study found that projected subsidence in year 2070 lowered 100-year storm water surface elevation in the channel about 1.4 feet, proportional to the projected subsidence of the watershed (1-2 feet). Both drivers, subsidence and land use, had minimal impact (less than 5%) on floodplain extent. Land use change increased peak discharge in the downstream channel by 39-55%. Flood depths increased significantly outside the channel due to subsidence which cause increased inundation of major roadways and neighborhood streets. During 100-year storm, neighborhood streets experienced an increase of approximately 4-6 inches of flood depth and major roads were inundated by up to an additional 14 inches. Currently, the Woodlands is subsiding 0.2-0.7 inches per year and the threat of subsidence is projected to increase due to local groundwater pumping. Local population is projected to increase 42%, increasing development and water demand. This study provides valuable information for water managers and decisionmakers about the hazardous flood implications subsidence and urbanization can induce.
Development of a Framework to Simulate Storm Surge-Induced Aboveground Storage Tank Spills
(2019-04-19) Do, Connie; Bedient, Philip B
This thesis introduces a modeling framework for simulating the surface trajectory of aboveground storage tank (AST) spills caused by flotation failure during storm surge events. A single tank failure can be catastrophic for neighboring residents, businesses, and wildlife as observed in the Murphy Oil spill during Hurricane Katrina. Presently, no modeling framework is available that can predict and simulate the advection of AST spills in a computationally efficient manner. To address this need, a loosely-coupled system of models is introduced here, which consists of a hydrodynamic model (SWAN+ADCIRC), an AST fragility model, and a Lagrangian particle tracking algorithm, to track spills on the order of minutes in a high-performance computing environment. The framework is applied to simulate spills in Galveston Bay, Texas and to evaluate the impact of storm surge mitigation on spill potential/trajectory. Findings indicate that spill location and bay geometry have strong controls on spill evolution. Additionally, the framework is versatile and can be used to calculate a variety of impact metrics. Finally, recommendations are made for future improvements to the framework. The ability to rapidly predict spill trajectory and impact can be a useful tool for emergency response deployment and sustainable engineering design.
Distributed Hydrologic Modeling of Large Storm Events in the Houston-Galveston Region
(2013-03-04) Deitz, Roni; Bedient, Philip B; Duenas-Osorio, Leonardo; Raun, Loren
In conjunction with the SSPEED Center, large rainfall events in the upper Gulf of Mexico are being studied in an effort to help design a surge gate to protect the Houston Ship Channel during hurricane events. When hurricanes hit Galveston Bay, there is a funneling effect and, depending on the track of the hurricane, the storm surge can vary by as much as 5 to 10 feet. For instance, Hurricane Ike produced a surge of about 13 feet in the bay; however, other tracks and higher winds could bring a worst case scenario of 20 to 25 feet of storm surge. Since the Houston Ship Channel is only protected from flooding up to 14-15 feet, and is currently the world’s second largest petrochemical complex, it is critical to understand the linkage between rainfall and storm surge to better protect the region. In this effort, rainfall events in the Houston-Galveston area are being examined. Given the large size of the watersheds flowing from the north and west, statistical methodologies, such as the Probable Maximum Precipitation (PMP) and Precipitation Depth Duration Frequency (PDDF), were employed to better design and predict the shape, pattern, size, and intensity of large rainfall events. Using Hydrometeorological Report (HMR) 52, as well as local hydrologic reports, the 24 hour PMP storm event was created for the upper Gulf of Mexico. In addition, large historic storms, such as Hurricane Ike, and simulated rainfalls from Hurricanes Katrina and Rita, were modeled over the Houston-Galveston region in a hydrologic/hydraulic model with the use of radar and rain gauge data. VfloTM, a distributed hydrologic model was used to model the aforementioned storms. The region was first calibrated to USGS stream gauge data from Greens Bayou Brays Bayou and Peach Creek, and the modeled results accurately depict key features of observed hydrographs, including time to peak, discharge, and the double peak discharge phenomenon caused by double rain bursts. Once calibrated, VfloTM, is used to quantify the effect that storm size, intensity, and location has on timing and peak flows in the upper drainage area. Results indicate that there is a double peak phenomenon with flows from the west draining earlier than flows from the north. With storm surge typically lasting 36-48 hours, this indicates the flows from the west and north are interacting with storm surge, with flows from the west arriving before flows from the north downstream. Gate operations were optimized in the model to account for the relative timing of upland runoff and hurricane surge, as well as the capability of the gate structure to protect the Ship Channel industry was quantified.
Quantifying Flood Risk and Hazard in Highly Urbanized Coastal Watersheds
(2016-10-17) Sebastian, Antonia Geerke; Bedient, Philip B
Today, nearly half of the global population lives within 150 km of a coastline. As continued coastal development coincides with rising sea levels and more frequent and intense storms, the incidence, and cost of natural disasters is expected to rise. In the United States, recent studies have shown that current flood hazard estimates widely under-predict actual flood losses in coastal areas, resulting in billions of dollars of avoidable damage. However, historical data for tropical cyclones (especially storm surge and precipitation) is often limited or insufficient for analyzing or predicting tropical cyclone impacts. Furthermore, floodplains, which drive policy decisions regarding local planning, new development, flood insurance, and flood mitigation, often oversimplify the complex processes associated with flooding in the coastal zone. This dissertation aims to improve existing methods for predicting flood hazards and associated risk in highly urbanized coastal watersheds by integrating currently available models into a multi-hazard framework. The research is divided into three phases: (1) characterizing storm surge behavior in Galveston Bay, (2) establishing boundary conditions for floodplain modeling, and (3) flood hazard and risk analysis. In the first phase, the coupled Simulating WAves Nearshore and ADvanced CIRCulation (SWAN+ADCIRC) Model is used to simulate storm surge in Galveston Bay. The results demonstrate that storm surge in the bay is dominated by local wind direction and landfall location. Furthermore, counterclockwise rotating winds cause the highest storm surges to occur in the heavily populated evacuation zones on the north and west shores of Galveston Bay. Thus, subsequent research focused on the Clear Creek Watershed which encompasses much of the heavily urbanized west side of Galveston Bay. The second phase focuses on modeling probable combinations of surge and precipitation for Clear Creek, located on the west side of Galveston Bay. To do so, a Non-parametric Bayesian Network based on copulas is built and combined with a 1-D bay model to stochastically simulate a large number of synthetic storms in the Gulf of Mexico. The Bayesian Network is computationally inexpensive and takes into consideration five tropical cyclone characteristics at landfall: windspeed, angle of approach, distance to landfall, radius of maximum winds, and forward velocity. The resulting network is flexible and can be easily expanded to incorporate additional data as it becomes available. In the final phase of research, flood hazard and risk in the watershed are modeled using a distributed hydrologic modeling software, Vflo(R), in combination with the hydraulic model, HEC-RAS. The dissertation culminates with a longitudinal assessment of the evolution of flood risk since 1970 in an urbanizing coastal watershed. Utilizing the proposed framework, the impact of localized land use/land cover (LULC) change on the spatial extent of flooding in the watershed and the underlying flood hazard structure are quantified. The results demonstrate that increases in impervious cover substantially increase the spatial extent of the floodplain, as well as the depth and frequency of flooding in neighborhoods within the 1\% floodplain. Finally, the analysis provides evidence that by incorporating physics-based distributed hydrologic models into floodplain studies, floodplain maps can be easily updated to reflect the most recent LULC information available. The methods presented in this dissertation have important implications for the development of mitigation strategies in coastal areas, such as deterring future development in flood prone areas and directing flood mitigation efforts in already flood prone communities.
Remapping Flood Hazard in Houston Using Stochastic Storm Transposition and Probabilistic Flood Modeling
(2023-04-20) Wyderka, Allison Michelle; Bedient, Philip B
This thesis proposes an alternative for mapping flood risk and applies the methodology to the Houston area, where recent storm events and subsequent flood damages have highlighted the need for improved flood risk mapping. Houston’s flat slopes, intense rain, and high urbanization cause significant flooding that is not captured in official floodplain maps. These floodplain maps form the basis of flood insurance requirements, so it is critical that they accurately represent the properties that are at risk of flooding. This thesis proposes the use of stochastic storm transposition, which is able to create artificial rainfall records on the order of hundreds of years while maintaining storm structure. This method is then used in conjunction with probabilistic modeling to account for uncertainty in rain events. While many studies have explored the use of probabilistic flood modeling to better map flood hazard, few studies have captured the range of uncertainty in the rainfall input due to spatiotemporal variation, duration, and intensity of rain events. Additionally, 2D hydraulic modeling is used to capture local flooding in addition to riverine flooding. The resulting flood hazard maps more reliably capture flood hazard than official FEMA floodplains maps, demonstrating that the methodology presented here in this thesis should be further explored and considered as an alternative to the current official floodplain maps.
Transformation and morphological impact of low-frequency waves during hurricane attack
(2019-06-05) Anarde, Katherine Alyse; Bedient, Philip B
Field measurements of wave, current, and sediment dynamics in the nearshore environment during extreme events are scarce due to energetic waves and rapid bed level changes that can damage or shift instrumentation. Overestimation of storm processes in many morphodynamic models highlight a need for high-resolution field data during extreme storm events to improve and validate model forecasts of coastal storm hazards and impacts. To address this data and knowledge gap, this thesis offers insights into the physical processes that contribute to coastal flooding and drive morphological change during storms by providing new field data, methodological frameworks, and detailed analysis of water levels, currents, and sediment transport on two mild-sloping beaches along the Texas Gulf coast (U.S.A) during Hurricane Harvey (2017). Measurements of storm hydrodynamics are linked to post-storm changes to coastal landforms using sedimentological data, beach profile surveys, and topographic maps derived from imagery collected by unmanned aerial vehicles. The comprehensive data set acquired during Hurricane Harvey is evaluated in multiple studies to examine the role of low-frequency surface ocean waves in driving coastal change and inland flooding during hurricane impact. Herein, "low-frequency waves" collectively refers to waves with frequencies spanning the infragravity (IG) band (0.003-0.04 Hz) and just below the IG band (~0.4-3 mHz), termed very low frequency (VLF) waves. Key findings include 1) IG wave growth and energy loss in the very nearshore and into the back-barrier bay during island overwash is frequency-dependent; 2) VLF variability in nearshore water levels can be classified as small-amplitude meteotsunamis, that when amplified, may present a flood hazard in this region; 3) the morphological evolution of barrier-island cuts during hurricane impact is influenced by competing wave-driven and back-barrier processes; and 4) sequential far-field storms may aid in the recovery of barrier beaches. The results obtained in this thesis will be used to inform validation studies to improve numerical simulations of the transformation and morphological impact of low-frequency waves toward better prediction of coastal hazards.
Watershed-scale Distributed Hydrologic Modeling and Assessment of Low Impact Development Features in White Oak Bayou, Houston, TX
(2015-01-27) Hughes, Christina M.; Bedient, Philip B; Li, Qilin; Nittrouer, Jeffery A; Vieux, Baxter E
This thesis proposes a method for modeling urban site-scale Low Impact Development (LID) features at the watershed-scale to evaluate the as-yet unknown performance of LID in a high intensity rainfall region. Increased impervious cover from urban development causes increased peak flows and shorter peak timing at the watershed outlet during rainfall events. Although LID features have been constructed across the U.S. to address these issues, their performance has not been evaluated in a high-intensity rainfall region or cumulatively throughout a large watershed. Using a fully-distributed Vflo® hydrologic model of the White Oak Bayou Watershed in Houston, TX, as opposed to conventional lumped-area models, two common urban retrofit LID features were modeled (rain gardens and green roofs) using a simple parameter-averaging method for various size storms. Findings indicate that although unable to significantly control the 100-year storm event, a combination of LID features can effectively reduce outlet discharges during smaller storms when fully implemented across a large watershed.

Browsing by Author "Bedient, Philip B"

Results Per Page

Sort Options