2014 CRC PhD Student Poster Session
33. Managing Water and Wastewater Infrastructure in Shrinking Cities Kasey Faust (faustk@purdue.edu), Advisor: Dr. Dulcy Abraham Purdue University The research presented in this poster highlights select water and wastewater infrastructure management challenges in shrinking cities, proposes management options to address these challenges, and evaluates the feasibility of a decommissioning, one of the management options. Major economic downturns in once vibrant industrial cities have resulted in the loss of significant populations and tax bases. This phenomenon, termed as shrinking cities, introduces enormous challenges to managing major infrastructure systems. When cities experience catastrophic economic conditions, consequentially causing extreme population loss, maintaining critical infrastructure at original levels of operation becomes unsustainable. While this study focuses on water and wastewater infrastructure, other forms of infrastructure (e.g., power and gas utilities) are equally susceptible. A key challenge affecting shrinking cities is the fixed costs of operations (approximately 75-80 percent of total cost) in spite of significantly declining populations and tax bases. As population continues to decline, the per capita cost for service increases. Decommissioning the excess, underutilized water infrastructure has the potential to reduce or stabilize these per capita service costs. A separate challenge impacting the wastewater system is reducing the quantity of runoff entering the combined sewer systems that are present in many shrinking cities. The quantity runoff may be reduced through decommissioning impervious surfaces and allowing the water to infiltrate the ground. Cities experiencing drastic urban shrinkage have the potential to shift land uses and selectively transition excess land from impervious to pervious surfaces to aid in meeting local, state, and federal regulations. The viability of decommissioning infrastructure components is examined for water infrastructure and wastewater infrastructure. EPANET, SWMM, L-THIA, and GIS are the primary tools used for analyses. A network analysis was performed using EPANET to examine how altering the topology of and changing demands within the network impacts the system’s performance using the metrics of adequate system pressures and fire flow capabilities. SWMM and L-THIA were used to evaluate the impact of decommissioning surfaces that contribute to runoff based on the percentage change in runoff from the status quo. The results yielded in SWMM and L-THIA were compared to estimate the differences in runoff quantities across different tools and assumptions. The metrics used and comparison of two tools allows for insight into decommissioning implications on system performance. Data incorporated in the models are gathered from city GIS databases and published literature. One Midwestern shrinking city that has experienced a loss of more than 40% of its population is used to demonstrate the feasibility of implementing the alternatives. The models were verified and validated by subject matter experts from Indiana and Michigan with backgrounds on issues inherent to shrinking cities, and water and wastewater infrastructure management or modeling experience. The results of the feasibility analysis for decommissioning water distribution pipelines and impervious surfaces illustrate the viability of proactively managing infrastructure, while providing adequate service levels, assisting in meeting regulations, improving aesthetics of the city, and potentially reducing or stabilizing service costs. By identifying issues inherent to shrinking cities and management options, city officials and decision makers are provided with insight that can be used to ensure effective and efficient long-term operation and management of water and wastewater infrastructure. Examining this new paradigm within cities of urban decline, aids in moving towards flexible infrastructure planning to accommodate future population trends, whether shrinking, static, or growing.
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