Scott C. Worland

Source, transport, and evolution of saline groundwater in a shallow Holocene aquifer on the tidal deltaplain of southwest Bangladesh

Deltaic groundwater resources are often vulnerable to degradation from seawater intrusion or through interaction with saline paleowaters. The Ganges-Brahmaputra-Meghna River delta, in Bangladesh and West Bengal, India, is a particularly vulnerable area with an estimated 20 million coastal inhabitants directly affected by saline drinking water. The shallow groundwater of the coastal regions is primarily brackish with pockets of fresher water. A small-scale hydrologic investigation of groundwater salinity beneath an embanked tidal channel island was undertaken to explore possible hydrogeological explanations of the distribution of water salinities in the shallow aquifer. This study employs a combination of 3H and 14C dating, electromagnetic subsurface mapping, and a 2-D solute transport model. The authors conclude that the shallow groundwater salinity can best be explained by the slow infiltration of meteoric water into paleo-brackish estuarine water that was deposited during the early-mid Holocene.

Measuring Urban Water Conservation Policies: Toward a Comprehensive Index

This article (1) discusses existing efforts to measure water conservation policies (WCPs) in the United States (U.S.); (2) suggests general methodological guidelines for creating robust water conservation indices (WCIs); (3) presents a comprehensive template for coding WCPs; (4) introduces a summary index, the Vanderbilt Water Conservation Index (VWCI), which is derived from 79 WCP observations for 197 cities for the year 2015; and (5) compares the VWCI to WCP data extracted from the 2010 American Water Works Association (AWWA) Water and Wastewater Rates survey. Existing approaches to measuring urban WCPs in U.S. cities are limited because they consider only a portion of WCPs or they are restricted geographically. The VWCI consists of a more comprehensive set of 79 observations classified as residential, commercial/industrial, billing structure, drought plan, or general. Our comparison of the VWCI and AWWA survey responses indicate reasonable agreement (ρxa0=xa00.76) between the two WCIs for 98 cities where the data overlap. The correlation suggests the AWWA survey responses can provide fairly robust longitudinal WCP information, but we argue the measurement of WCPs is still in its infancy, and our approach suggests strategies for improving existing methods.

Improving predictions of hydrological low-flow indices in ungaged basins using machine learning

Abstract We compare the ability of eight machine-learning models (elastic net, gradient boosting, kernel-k-nearest neighbors, two variants of support vector machines, M5-cubist, random forest, and a meta-learning ensemble M5-cubist model) and four baseline models (ordinary kriging, a unit area discharge model, and two variants of censored regression) to generate estimates of the annual minimum 7-day mean streamflow with an annual exceedance probability of 90% (7Q10) at 224 unregulated sites in South Carolina, Georgia, and Alabama, USA. The machine-learning models produced substantially lower cross validation errors compared to the baseline models. The meta-learning M5-cubist model had the lowest root-mean-squared-error of 26.72 cubic feet per second. Partial dependence plots show that 7Q10s are likely moderated by late summer and early fall precipitation and the infiltration capacity of basin soils.

Urban Water Conservation Policies in the United States

Urban water supply systems in the United States are increasingly stressed as economic and population growth confront limited water resources. Demand management, through conservation and improved efficiency, has long been promoted as a practical alternative to building Promethean energy-intensive water-supply infrastructure. Some cities are making great progress at managing their demand, but study of conservation policies has been limited and often regionally focused. We present a hierarchical Bayesian analysis of a new measure of urban water conservation policy, the Vanderbilt Water Conservation Index (VWCI), for 195 cities in 45 states in the contiguous United States. This study does not attempt to establish causal relationships, but does observe that cities in states with arid climates tend to adopt more conservation measures. Within a state, cities with more Democratic-leaning voting preferences and large and rapidly growing populations tend to adopt more conservation measures. Economic factors and climatic differences between cities do not correlate with the number of measures adopted, but they do correlate with the character of the measures, with arid cities favoring mandatory conservation actions and cities in states with lower real personal income favoring rebates for voluntary actions. Understanding relationships between environmental and societal factors and cities’ support for water conservation measures can help planners and policy-makers identify obstacles and opportunities to increase the role of conservation and efficiency in making urban water supply systems sustainable.