• Canada
• 020701 environmental engineering close

Electrical resistivity imaging has been successfully used to monitor near-surface hydrologic processes but use of standard measurement arrays may not provide the greatest data sensitivity to the imaged region. We present a method of experimental design based on the concept of informed imaging for creating an electrical resistivity imaging experiment to monitor flow beneath a recharge pond. Informed imaging is the integration of all available data about a site into the acquisition, inversion and interpretation of electrical resistivity data. Informed experimental design uses all available information to develop an a priori model of the subsurface conductivity structure that guides the selection of measurement arrays for an electrical resistivity imaging experiment given spatial and temporal constraints on the acquisition. Selection of arrays focuses on maximizing the amount of unique information acquired with each source pair. We apply the method to the selection of arrays for imaging the top 5 m of the subsurface beneath a recharge pond in Northern California, which is part of an aquifer storage and recovery project. Decreasing infiltration rates over time reduce the effectiveness of the recharge pond. We seek to monitor infiltration processes at the contact between a fines-rich sand layer and coarser sand layer in an effort to understand the hydrologic controls on infiltration. The performance of the arrays selected using informed experimental design relative to two standard arrays (Wenner and dipole-dipole) is validated on two synthetic subsurface conductivity models, which are representative of conductivity structures that may arise during an infiltration event. Performance is evaluated in terms of a singular value decomposition of the sensitivity matrix produced by the three types of arrays, as well as a measure of the region of investigation. Results demonstrate that arrays selected using informed experimental design provide independent information about the imaged region and are robust in the presence of noise, improving the ability to image changes in a conductivity structure that result from infiltration processes.

Summarization: An assessment of the impact of global climate change on the water resources status of the island of Crete, for a range of 24 different scenarios of projected hydro-climatological regime is presented. Three “state of the art” Global Climate Models (GCMs) and an ensemble of Regional Climate Models (RCMs) under emission scenarios B1, A2 and A1B provide future precipitation (P) and temperature (T) estimates that are bias adjusted against observations. The ensemble of RCMs for the A1B scenario project a higher P reduction compared to GCMs projections under A2 and B1 scenarios. Among GCMs model results, the ECHAM model projects a higher P reduction compared to IPSL and CNCM. Water availability for the whole island at basin scale until 2100 is estimated using the SAC-SMA rainfall–runoff model And a set of demand and infrastructure scenarios are adopted to simulate potential water use. While predicted reduction of water availability under the B1 emission scenario can be handled with water demand stabilized at present values and full implementation of planned infrastructure, other scenarios require additional measures and a robust signal of water insufficiency is projected. Despite inherent uncertainties, the quantitative impact of the projected changes on water availability indicates that climate change plays an important role to water use and management in controlling future water status in a Mediterranean island like Crete. The results of the study reinforce the necessity to improve and update local water management planning and adaptation strategies in order to attain future water security. Presented on: Journal of Hydrology

Recent evidence shows that the variability of meridional overturning circulation (MOC) in the Indian and Pacific Oceans (PMOC) is characterized by a prominent deep cross-equatorial cell (CEC) spanning the tropics between 20S and 20N, but the mechanism responsible for this CEC is not understood. Using version 4.2 of the Estimating the Circulation and Climate of the Ocean (ECCO) state estimate, our investigation shows the mechanism responsible for CEC can be conceptualized by following mechanistic chain: 1) Anomalous winds produce equatorially antisymmetric anomalies of zonal mean sea surface temperature (SST) in the Pacific Ocean, 2) These temperature anomalies generate equatorially antisymmetric anomalies of sea surface height (SSH), 3) The SSH anomalies generate a cross-equatorial flow in the upper Pacific Ocean, and 4) This anomalous cross-equatorial flow in the upper layers drives compensating circulation in the deep Pacific.

Abstract. We calculated dimensional change for 33 glaciers in the Cariboo Mountains of British Columbia for the latter half of the twentieth century. All glaciers receded during the period 1952–2005; area retreat averaged −0.19 ± 0.05% a−1. From 1952 to 1985, nine glaciers advanced. Following 1985, retreat rates accelerated to −0.41 ± 0.12% a−1. Thinning rates likewise accelerated, from −0.14 ± 0.04 m w.e. a−1 (1952–1985) to −0.50 ± 0.07 m w.e. a−1 for the period 1985–2005. Temperatures increased from the earlier to the latter period for the ablation (+0.38 °C) and accumulation (+0.87 °C) seasons, and average precipitation decreased, particularly in the accumulation season (−32 \\unit{mm}, −3.2%). Our comparison of surface area change with glacier morphometry corroborates previous studies that show primary relations between extent change and surface area. We also find, however, that the strength and sign of these relations varied for different epochs.

Abstract Developing strategies to identify the origins of contaminants in watersheds is crucial for source water protection. The use of multiple tracers improves the ability to identify contamination events originating from various land use activities. The objective of this study was to evaluate the use of acesulfame and chloride as co-tracers to represent the impact of pollution originating from wastewater and road de-icing on water quality in a municipal drinking water source. The study included a two-year sampling and water quality analysis program in numerous locations within a drinking water reservoir comprising a lake (upstream) and a river (downstream) which supply raw water to a municipal water treatment plant. Results showed that the spatial variability of acesulfame and chloride within the watershed of the lake-river systems depends on the location of contaminant sources, mainly municipal wastewater and septic tank discharges (for acesulfame) and the presence of small tributaries of the lake and river (for chloride). Temporal variability of the tracers under study differed according to the sampling location and was mainly affected by seasonal conditions. Correlation analyses between the two tracers in lake and river waters (in terms of concentrations and loads) made it possible to pinpoint the probable origins of contamination. The assessment of the spatio-temporal variability of these co-tracers within the lake-river watersheds allowed for the delineation of priority intervention zones as a decision-making tool for municipal authorities in improving drinking water source protection.

Laboratory experiments in geomorphology is the theme of the 46th annual Binghamton Geomorphology Symposium (BGS). While geomorphic research historically has been dominated by field-based endeavors, laboratory experimentation has emerged as an important methodological approach to study these phenomena, employed primarily to address issues related to scale and the analytical treatment of the geomorphic processes. It is contended here that geomorphic laboratory experiments have resulted in transformative research. Several examples drawn from the fluvial and aeolian research communities are offered as testament to this belief, and these select transformative endeavors often share very similar attributes. The 46th BGS will focus on eight broad themes within laboratory experimentation, and a strong and diverse group of scientists have been assembled to speak authoritatively on these topics, featuring several high-profile projects worldwide. This special issue of the journal Geomorphology represents a collection of the papers written in support of this symposium.

Many people think of transboundary water in terms of national security. However, water is not, nor is it likely to become, a cause of war. Rather, the need is for water security, which implies that water management must balance the goals of efficiency, equity, sustainability and implementability. This article suggests how a joint management structure for fresh water can be designed to promote ongoing resolution of issues, and do so in a way that de-nationalizes and de-securitizes transboundary water. Though designed with the Israeli–Palestinian case in mind, the approach is applicable wherever water divides rather than unites states or peoples.

Abstract To predict the rate and consequences of shrinkage of the earth’s mountain glaciers and ice caps, it is necessary to have improved regional-scale models of mountain glaciation and better knowledge of the subglacial topography upon which these models must operate. The problem of estimating glacier ice thickness is addressed by developing an artificial neural network (ANN) approach that uses calculations performed on a digital elevation model (DEM) and on a mask of the present-day ice cover. Because suitable data from real glaciers are lacking, the ANN is trained by substituting the known topography of ice-denuded regions adjacent to the ice-covered regions of interest, and this known topography is hidden by imagining it to be ice-covered. For this training it is assumed that the topography is flooded to various levels by horizontal lake-like glaciers. The validity of this assumption and the estimation skill of the trained ANN is tested by predicting ice thickness for four 50 km × 50 km regions that are currently ice free but that have been partially glaciated using a numerical ice dynamics model. In this manner, predictions of ice thickness based on the neural network can be compared to the modeled ice thickness and the performance of the neural network can be evaluated and improved. From the results, thus far, it is found that ANN depth estimates can yield plausible subglacial topography with a representative rms elevation error of ±70 m and remarkably good estimates of ice volume.

Dam building and reservoir operations alter the downstream hydrological regime, and as a result, affect the health of the river aquatic ecosystem, particularly for large-scale cascade reservoirs. This study investigated the impact of the Gezhouba Reservoir (GR) and the Three Gorges Reservoir (TGR) on the spawning conditions of two critical taxa, i.e., the endemic four major carps and the endangered Chinese sturgeon in the Yangtze River. We analyzed the flow, sediment, and thermal regime in these two taxa spawning seasons and compared their features between the predam and postdam periods. Our results revealed that the GR and the TGR had altered the frequency distributions of flow, sediment, and water temperature to different degrees, with the impact by the GR on the carps and Chinese sturgeon ranked as water temperature > flow, sediment > water temperature > flow, and the effect of the TGR on these two taxa were ordered as flow > water temperature, sediment > flow > water temperature. For the GR, the satisfying degree of the suitable flow and water temperature of the carps increased, whilst the suitable flow, sediment, and water temperature for the Chinese sturgeon decreased. These changes in TGR showed a significant ascending (descending) trend in the suitable flow (water temperature) for the carps, and a clear decreasing trend in the flow, sediment, and temperature for Chinese sturgeon. Both the TGR and the GR had negative impacts on the spawning of these two taxa in terms of the rising/falling flow characteristics.