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Potential impact of climate changes on the inundation risk levels in a dam break scenario

Potential impact of climate changes on the inundation risk levels in a dam break scenario

Sudha Yerramilli
Urban Planning, Jackson State University
December, 2009
 
Sudha Yerramilli, Ph.D., has over 10 years of GIS experience and is currently working as a GIS Specialist at National Center for Biodefense Communications. She has 7 years of experience in Environmental Planning and has conducted various environmental impact studies. Her areas of expertise are application of GIS and Remote Sensing for Planning, development of web based information tools for geospatial decision support systems using ArcGIS, ArcIMS and integration of hydrological models like HEC-RAS for flood risk assessment and disaster management research.
 

Abstract

The dynamic nature of urban planning requires the integration of multi- disciplinary information to facilitate the decision making and implementation processes. For efficient participation from all the stakeholders, dissemination of information plays a crucial role. Development of applications can act as information tools through which authorities as well as the public understand the current situation of their communities and contribute to the planning process with invaluable inputs and feedbacks. Analysis of spatial and statistical information in terms of forecasting, modeling and evaluation of present and future scenarios can assist planning with crucial information. This dissertation proposal focuses on developing a web application using Arc IMS, where the information about flood inundation risk levels at the downstream of the Ross Barnett Reservoir at various climatic events (different precipitation levels) will be made accessible to the decision making authorities and public.
The climatic changes, with increase in temperature and rainfall, have disastrous consequences that impact the physical systems, infrastructure and social organization in many ways. Floods/flash floods due to dam breaks can be categorized as the high-impact events as they involve multiple consequences. The damage can be far more severe and accumulative to the State of Mississippi with 277 high hazard dams, 67 significant hazard dams across the State, and with a prediction of 5-25% increase in rainfall from the last century. As flooding is associated with rainfall levels, this study
aims at assessing the potential impact of climate change on various precipitation events on the inundation risk levels in the Ross Barnett Reservoir dam break scenario. The impact of the failure of this high hazard dam (which is nearing its design life time of 50 years in 2010) may involve disastrous consequences with the Mississippi state capital (the City of Jackson) located in the immediate downstream region.
The average precipitation event calculated from100-years historical data is 5.39 inches. An increase of 10% and 25% on the average would be 5.929 and 6.7375 inches respectively. The PMP event has occurred in the month of April 1991 with a recorded rainfall of 16.75 inches. As the flood simulations using PMP event can capture the 10% and 25% increase on the average rainfall events, the study aims to simulate the worst case scenarios (that could happen due to climate change effects) and an increase of 50% and 100% on the PMP event is included.
For the purpose of the study, inundation maps are generated by simulating the dam break model HEC RAS/GEO-RAS for various scenarios and the output is integrated with the thematic layers of the study region by overlaying the inundation map using Arc GIS. The Ross Barnett Reservoir failure under the impact of climate changes affects the downstream region in terms of spatial extent and depth grids till the end of Hinds County. While the possible least scenario in an average rainfall event itself has tremendous impact on the downstream, the PMP rainfall event almost equals a 200-year flood magnitude. With the PMP event been already experienced by the study region (in April 1991), the scenario of the Ross Barnett Reservoir failure in this event bears high possibility and utmost significance.
As the developmental activities in the downstream region, including state capital, Jackson, are bound to NFIP generated 100-year flood maps, the impact of Ross Barnett Reservoir failure proves to be far more destructive. The flood maps (from average rainfall event to PMP+100% event) obtained from the simulations reveal the fact that the impact of Ross Barnett Reservoir failure on the cultural/historical, economical, social, infrastructural amenities can disturb the inter-connected functionalities of the state capital. As the downtown region is surrounded by flood waters in all the four rainfall scenarios, administrative and commercial functionalities can come to a stand still. The results reveal the fact that the basic intentions of planning or developmental strategies are to build safer communities by locating developments away from the hazard-prone areas. Identifying vulnerable areas under various possible scenarios plays an important role in the decision-making process. The increase in the vulnerability levels that might occur due to climate change affects in the downstream of Ross Barnett Reservoir can help the local government to improve the inclusive nature of environmental factors to their focus on achieving sustainable development.
Finally, the study developed an Arc IMS web application where the information about the inundation risk levels at various precipitation scenarios at the Ross Barnett Reservoir are made accessible so that the information can be interpreted and utilized quickly and easily by the decision making authorities and public.