Field Demonstrations Using the Waterloo Ground Water Profiler

Use of direct-push sampling tools fur rapid investigations of contaminated sites has proliferated in the past several years. A direct-push device, referred to as a ground water sampling profiler, was recently developed at the University of Waterloo. This tool differs from oilier direct-push tools in that point samples are collected at multiple depths in the same hole without retrieving, decontaminating, and re-driving the tool alter each sampling event. The collection of point samples, rather than samples from a longer screened interval, allows an exceptional level of detail to be generated about the vertical distribution of contamination from each hole. The benefits of acquiring this level of detail arc contingent on minimization of vertical cross contamination of samples caused by drag down from high concentration zones into underlying low concentration zones. In a detailed study of chlorinated solvent plumes in sandy aquifers, we found that drag down using the profiler is minimal or non-detectable even when the tool is driven through high concentration zones of dissolved chlorinated solvent contamination. Chlorinated solvent concentrations, primarily PCE and TCE at or below a detection limit of 1 μg/L, were obtained directly beneath plumes with maximum concentrations up to thousands of μg/L. Minimal drag down, on the order of a few μg/L to 20 μg/L, may have been observed below chlorinated solvent concentrations of several tens of thousands to hundreds of thousands of μg/L. Drag down through DNAPL zones was not evaluated.     

Hydrologic simulation approach for El Niño Southern Oscillation (ENSO)-affected watershed with limited raingauge stations

ABSTRACT

Since the performance of hydrological models relies on numerous factors, the selection of an appropriate modeling approach for hydrological study has always been a crucial issue. The major objective of this research is to demonstrate that data-driven models such as the Adaptive Neuro-Fuzzy Inference system (ANFIS) are more suitable in a region where spatially distributed precipitation datasets are not available. Since precipitation has a teleconnection with the El Niño Southern Oscillation (ENSO) in different parts of the world, the sea surface temperatures (SSTs) and sea level pressures (SLPs) of the equatorial Pacific can be expected to act as surrogates for the precipitation if there are insufficient raingauge stations in the watershed. Moreover, in contrast to conceptual and physically-based models, data driven models can incorporate SST and SLP in their input vectors, and hence additional forcing of SST with precipitation has been experimented with in past studies. Therefore, our second objective is to test whether the additional forcing of SST and SLP will improve the hydrologic simulation. For this, various ANFIS models for the winter season were developed considering 10 raingauge stations situated at various locations in the watershed. Rainfall from each raingauge station was considered in the ANFIS model one at a time with and without SST/SLP. The results show that the performance of the ANFIS model improved with the additional fusion of SST and SLP, especially when a raingauge station from a remote location was considered. However, this improvement was observed when the analysis was primarily focused on the winter season which is a period with a strong ENSO signal.

Editor D. Koutsoyiannis Associate editor L. See     

A New Delhi every day: multiplicities of governance regimes in a transforming metropolis

In this article I demonstrate the coexistence of multiple urban governance regimes in Delhi, India. While formal urban governance is geared toward transforming Delhi into a “world-class” city, I present original research that shows how the everyday governance of urban space in three very different areas of Delhi is determined by relations among non-state actors. These regimes foster access to space for street hawkers on an everyday basis while they allow powerful local interest groups to collect rent and influence flows of people and commodities. I argue that, in contrast to formal electoral politics, these governance regimes emerge from a parallel politics of everyday interactions, negotiations, and transgressions. Although the emancipatory potential of these regimes should not be overstated, they do offer street hawkers limited contingency to improve their access to urban space. This article contributes to a growing body of work on urban governance by showing how multiplicities of governance regimes coexist and determine how and by whom urban space is used in a metropolis in the global South.     

Effect of irrigation pumpage during drought on karst aquifer systems in highly agricultural watersheds: example of the Apalachicola-Chattahoochee-Flint river basin,southeastern USA

In the Apalachicola-Chattahoochee-Flint (ACF) river basin in Alabama, Georgia, and Florida (USA), population growth in the city of Atlanta and increased groundwater withdrawal for irrigation in southwest Georgia are greatly affecting the supply of freshwater to downstream regions. This study was conducted to understand and quantify the effect of irrigation pumpage on the karst Upper Floridan Aquifer and river–aquifer interactions in the lower ACF river basin in southwest Georgia. The groundwater MODular Finite-Element model (MODFE) was used for this study. The effect of two drought years, a moderate and a severe drought year, were simulated. Comparison of the results of the irrigated and non-irrigated scenarios showed that groundwater discharge to streams is a major outflow from the aquifer, and irrigation can cause as much as 10 % change in river–aquifer flux. The results also show that during months with high irrigation (e.g., June 2011), storage loss (34 %), the recharge and discharge from the upper semi-confining unit (30 %), and the river–aquifer flux (31 %) are the major water components contributing towards the impact of irrigation pumpage in the study area. A similar scenario plays out in many river basins throughout the world, especially in basins in which underlying karst aquifers are directly connected to a nearby stream. The study suggests that improved groundwater withdrawal strategies using climate forecasts needs to be developed in such a way that excessive withdrawals during droughts can be reduced to protect streams and river flows.     

Accurate Ocean Bottom Seismometer Positioning Method Inspired by Multilateration Technique

The positioning of ocean bottom seismometers (OBS) is a key step in the processing flow of OBS data, especially in the case of self popup types of OBS instruments. The use of first arrivals from airgun shots, rather than relying on the acoustic transponders mounted in the OBS, is becoming a trend and generally leads to more accurate positioning due to the statistics from a large number of shots. In this paper, a linearization of the OBS positioning problem via the multilateration technique is discussed. The discussed linear solution solves jointly for the average water layer velocity and the OBS position using only shot locations and first arrival times as input data.     

Two‐dimensional flow patterns near contour grass hedges

Grass hedges are narrow strips of stiff‐stemmed vegetation used to control erosion and sediment delivery. When planted on the contour, the hydraulic resistance of the vegetation slows runoff, creates ponding, and promotes sediment deposition. When tillage is performed between grass hedges, soil may be thrown against the vegetation, where it settles to form a berm within the hedge. Tillage‐induced berms divert part of runoff, causing it to flow alongside the hedge without crossing it. Such flow partitioning created by grass hedges was measured on experimental plots located on silt loam loess soil near Holly Springs, Mississippi, USA, where hedges planted at the bottom of 5%, 22.1‐m‐long slopes evolved berms averaging 0.13 m in height. They diverted about 80% of the runoff for events smaller than 5 mm and about 50% for large events. A two‐dimensional model was developed to determine overland flow patterns over complex terrains, accounting for oriented roughness created by tillage corrugations, crop rows, and larger features such as berms and vegetative barriers. The model was used to reproduce the flow partition observed in the field experiments and to determine how berm height and slope steepness and length affected runoff redistribution. Numerical simulations indicated that for most runoff events, ponded runoff depths were not high enough to overtop the berm but rather crossed the berms through cracks and gaps, represented in the model as small triangular weirs. The model also was applied to a 6.0‐ha watershed in Western Iowa, USA, where nine grass hedges were planted across 12–16% slopes. Computed dynamic flow properties showed that berms increased the amount of runoff flowing laterally upslope of the hedges and that a large portion of the runoff crossed the vegetative strips at a few locations and with high flow depths, increasing the risk of development of ephemeral gullies. Copyright © 2011 John Wiley & Sons, Ltd.