Managed Aquifer Recharge as a Tool to Enhance Sustainable Groundwater Management in California

A growing population and an increased demand for water resources have resulted in a global trend of groundwater depletion. Arid and semi-arid climates are particularly susceptible, often relying on groundwater to support large population centers or irrigated agriculture in the absence of sufficient surface water resources. In an effort to increase the security of groundwater resources, managed aquifer recharge (MAR) programs have been developed and implemented globally. MAR is the approach of intentionally harvesting and infiltrating water to recharge depleted aquifer storage. California is a prime example of this growing problem, with three cities that have over a million residents and an agricultural industry that was valued at 47 billion dollars in 2015. The present-day groundwater overdraft of over 100 km3 (since 1962) indicates a clear disparity between surface water supply and water demand within the state. In the face of groundwater overdraft and the anticipated effects of climate change, many new MAR projects are being constructed or investigated throughout California, adding to those that have existed for decades. Some common MAR types utilized in California include injection wells, infiltration basins (also known as spreading basins, percolation basins, or recharge basins), and low-impact development. An emerging MAR type that is actively being investigated is the winter flooding of agricultural fields using existing irrigation infrastructure and excess surface water resources, known as agricultural MAR. California therefore provides an excellent case study to look at the historical use and performance of MAR, ongoing and emerging challenges, novel MAR applications, and the potential for expansion of MAR. Effective MAR projects are an essential tool for increasing groundwater security, both in California and on a global scale. This chapter aims to provide an overview of the most common MAR types and applications within the State of California and neighboring semi-arid regions

Electrical characterization of cadmium zinc telluride nanowires for use as a gamma radiation detector: Modeling and experimentation

Cadmium Zinc Telluride (CZT) is a universal single crystal room temperature ternary compound semiconductor used for radiation detection. These semiconductor detectors are limited to a size of 2mm wafers and the cost to create low defect density samples is very high. The purpose of this thesis is to measure the electrical characteristics of CZT nanowires electrodeposited onto a titanium dioxide (TiO2) nanotubular template grown from titanium (Ti) substrate. Voltage-current (V-I) characteristics were measured to test the feasibility of using this material as a detector of gamma radiation. First the measurements were conducted on single CZT nanowire samples, and then on stacked arrays of multiple samples connected in series. The experiments used two low energy radiation sources, Americium-241, a source of 60keV, 4μCurie gamma radiation and Iodine-129 a source of 30keV, 0.1μCurie x ray radiation. These sources are calibration tools obtained from the National Institute of Standards and Technology (NIST). The experiments show that the stacked arrays of CZT nanowire samples are good candidates for detecting low energy gamma radiation at room temperature. Unexplained oscillations in the V-I characteristics were thought to be related to defects in the material or due to possible penetration of the silver (Ag) epoxy that was used for making electrical contact with the gold (Au) sputtered electrodes. This possibility was numerically modeled by software Maxwell 3D® (Ansoft Co., Canonsburg, PA, version 11.1). In addition to the V-I characteristic measurements, an attempt was made to incorporate the CZT nanowire array detector array into a spectrometer setup. Preliminary measurements did not show any response from the CZT nanowire array to gamma radiation. Suggestions are made in the thesis for improving the detector design that would potentially lead to a response to gamma radiation