Development of a Numerical Multi-Layered Groundwater Model to Simulate Inter-Aquifer Water Exchange in Shelby County, Tennessee

Inter-aquifer water exchange between the shallow and Memphis aquifers in Shelby County, Tennessee may pose a contamination threat due to the downward migration of younger, poor quality groundwater into deeper, more pristine aquifer. Discontinuities (breaches) in the upper Claiborne confining unit (UCCU) allow for leakage into the Memphis aquifer, a sand-dominated aquifer that provides about 95% of the groundwater used in the Memphis area. This study created a multi-layered 3D groundwater model for Shelby County using the United States Geological Survey’s MODFLOW-NWT program to evaluate water exchange for a simulation period from January 2005 to December 2016. Results indicate an overall leakage through the UCCU of 61 m3/min into the Memphis aquifer in Shelby County, accounting for 10% of its water budget inflow, with localized areas experiencing as much as 20% water exchange. As young water tends to stay in the upper part of the Memphis aquifer, water budget assessment for the upper 60 m of the Memphis aquifer revealed leakage representing 29% of the zone inflow, and as much as 53% in certain areas. More localized studies must be conducted to understand the location, characteristics, and orientation of the confining unit breaches, as well as the inter-aquifer water exchange.

Congestion and observability across interdependent power and telecommunication networks under seismic hazard

This article quantifies the seismic performance of interdependent electric power and telecommunication systems, while also identifying variables with the highest impact on design. We introduce interdependent power and telecommunication models, which probabilistically simulate the physical dependency of telecommunication systems on power via interdependent adjacency and coupling strength, while a topology observability analysis quantifies the cyber dependency of the power system on telecommunications. We also use new functionality-based performance measures, including data congestion in telecommunications and partial observability in power systems, given communication demands upsurging after earthquakes. As an application, our methodology assesses the performance of stylized power and telecommunication systems in Shelby County, TN. Results show that neglecting retrials, congestion, and power interdependency lead to significant overestimation of the performance of telecommunication systems, particularly at low-to-medium hazard levels. Sensitivity results also reveal that decreasing the strength of coupling across systems is one of the most effective ways to improve the seismic performance of evolving cyber-physical systems, particularly when increasing observability in the power system through telecommunication end offices with richer data flow pathways.

Editor’s Corner

Last year I published an editorial about voting during the pandemic, contrasting states trying to make voting more accessible, with states that were fighting efforts to enable ways citizens could vote safely. Unfortunately greater voting access is under more attack now. The Brennan Center for Justice noted as of March 24th, “361 bills with restrictive provisions in 47 states. That’s 108 more than the 253 restrictive bills tallied as of February 19, 2021—a 43 percent increase in little more than a month.” This is very disappointing, and once again my home state of Texas is restricting access, trying to ban methods of voting that local officials allowed during the pandemic in last year’s general election. The Texas Senate recently passed Senate Bill 7, which would limit extended early voting hours, prohibit drive-thru voting, and make it illegal for local election officials to proactively send applications to vote by mail. Here’s hoping the Texas House will stand up to the Texas Senate and not restrict the ways citizens of Texas can vote. I think it also demonstrates that the U.S. Supreme Court was premature in its 2013 Shelby County v. Holder ruling removing the requirement that states with a history of racial discrimination in voting get pre-clearance from the Justice Department before making changes in voting procedures. With so many states trying to restrict voting, and limit the powers of election officials, the U.S House has passed H.R. 1, For the People Act of 2021, in early March. This bill addresses voter access, election integrity and security, and more. Hopefully this will pass the U.S. Senate and allow the citizens of the United States the right to vote without undue burdens.

Community vulnerability perspective on robust protection planning in interdependent infrastructure networks

Critical infrastructure networks, including water, power, communication, and transportation, among others, are necessary to society’s functionality. In recent years, the threat of different types of disruptions to such infrastructure networks has become an increasingly important problem to address. Due to existing interdependencies, damage to a small area of one of the networks could have far-reaching effects on the ability to meet demand across the entire system. Common disruption scenarios include, among others, intentional malevolent attacks, natural disasters, and random failures. Similar works have focused on only one type of scenario, but combining a variety of disruptions may lead to more realistic results. Additionally, the concept of social vulnerability, which describes an area’s ability to prepare for and respond to a disruption, must be included. This should promote not only the protection of the most at-risk components but also ensure that socially vulnerable communities are given adequate resources. This work provides a decision making framework to determine the allocation of defensive resources that accounts for all these factors. Accordingly, we propose a multi-objective mathematical model with the objectives of: (i) minimizing the vulnerability of a system of interdependent infrastructure networks, and (ii) minimizing the total cost of the resource allocation strategy. Moreover, to account for uncertainty in the proposed model, this paper incorporates a means to address robustness in finding the most adaptable network protection plan to reduce the vulnerability of the system of interdependent networks to a variety of disruption scenarios. The proposed work is illustrated with an application to social vulnerability and interdependent power, gas, and water networks in Shelby County, Tennessee.