Hydrologic and water isotope characterization of a regulated Canadian Shield river basin

Stable water isotope surveys have increasingly been integrated into river basins studies, but fewer have used them to evaluate impact of hydropower regulation. This study applies hydrologic and water isotope survey approaches to a Canadian Shield river basin with both regulated and natural flows. Historical streamflow records were used to evaluate the influence of three hydroelectric reservoirs and unregulated portions of the basin on downstream flows and changes in water level management implemented after an extreme flood year (1979). In 2013, water isotope surveys of surface and source waters (e.g., rainfall, groundwater, snowmelt) were conducted to examine spatial and temporal variation in contributions to river flow. Seasonal changes in relative groundwater contribution were assessed using a water‐isotope mass balance approach. Within the basin, two regulated reservoirs exhibited inverted hydrographs with augmented winter flows, whereas a third exhibited a hydrograph dominated by spring snowmelt. In 2013, spatial variation in rain‐on‐snow and air temperatures resulted in a critical lag in snowmelt initiation in the southern and northern portions of the basin resulting in a dispersed, double peak spring hydrograph, contrasting with 1979 when a combination of rain‐on‐snow and coincident snowmelt led to the highest flood on record. Although eastern basin reservoirs become seasonally enriched in δ¹⁸O and δ²H values, unregulated western basin flows remain less variable due to groundwater driven baseflow with increasing influence downstream. Combined analysis of historical streamflow (e.g., flood of 1979, drought of 2010) and the 2013 water isotope surveys illustrate extreme meteorological conditions that current management activities are unable to prevent. In this study, the influence of evaporative fractionation on large surface water reservoirs provides important evidence of streamflow partitioning, illustrating the value of stable water isotope tracers for study of larger catchments.     

Scaling procedures for heterogeneous unconfined aquifers

Complex flows in heterogeneous confined and unconfined aquifers is a phenomenon that continues to present difficulties in flow mapping and modelling in the field, laboratory, and through numerical simulations. It is often the case with complicated phenomena that transformative scaling and reduction of the problem through symmetry is of great efficacy in the formation of predictive models in both the laboratory and computational settings. A detailed a study of the application of a broad class of Lie scaling transformations on a set of equations representing the groundwater flows in heterogeneous confined and unconfined aquifers has produced a set of scaling relationships between the spatial variables, hydrologic variables, and parameters. The set of scaling transformations preserve the structure of the equations in the sense that the scaling transformations leave the initial‐boundary value system representing the invariant groundwater flows. This theoretical approach elucidates not only the scaling relationships but also the properties that hydrologic variables and parameters must satisfy in order for calling to be possible. Validation of the theory developed is carried out through a series of four numerical simulations using the USGS modflow ‐2005 software package. The results of these experiments demonstrate that the derived scaling transformations can effectively form predictive models of large‐scale phenomena at small scales with negligible error in many cases. Comments on the limitations of the approach and directions for future research are made in the closing sections. Copyright © 2016 John Wiley & Sons, Ltd.     

Erodibility of low‐compaction steep‐sloped reclaimed surface mine lands in the southern Appalachian region,USA

The use of loose spoils on steep slopes for surface coal mining reclamation sites has been promoted by the US Department of Interior, Office of Surface Mining for the establishment of native forest, as prescribed by the Forest Reclamation Approach (FRA). Although low‐compaction spoils improve tree survival and growth, erodibility on steep slopes was suspected to increase. This study quantified a combined K_C factor (combining the effects of the soil erodibility K factor and cover management C) for low compaction, steep‐sloped (>20°) reclaimed mine lands in the Appalachian region, USA. The combined K_C factor was used because standard Unit Plot conditions required to separate these factors, per Revised Universal Soil Loss Equation (RUSLE) experimental protocols, were not followed explicitly. Three active coal mining sites in the Appalachian region of East Tennessee, each containing four replicate field plots, were monitored for rainfall and sediment yields during a 14‐month period beginning June 2009. Average cumulative erosivity for the study sites during the monitoring period was measured as 5248.9 MJ·mm·ha^?1·h^?1. The K_C ranged between 0.001 and 0.05 t·ha·h·ha^?1·MJ^?1·mm^?1, with the highest values occurring immediately following reclamation site construction as rills developed (June – August 2009). The K_C for two study sites with about an 18–20 mm spoil D₈₄ were above 0.01 t·ha·h·ha^?1·MJ^?1·mm^?1 during rill development, and below 0.003 t·ha·h·ha^?1·MJ^?1·mm^?1 after August 2009 for the post‐rill development period. The K_C values for one site with a 40 mm spoil D₈₄ were never above 0.008 t·ha·h·ha^?1·MJ^?1·mm^?1 and also on average were lower, being more similar to the other two sites after the rill development period. Based on an initial K_C factor (K_e) measured during the first few storm events, the average C factor (C_e) was estimated as 0.58 for the rill development period and 0.13 for the post‐rill development period. It appears that larger size fractions of spoils influence K_C and C_e factors on low‐compaction steep slopes reclamation sites. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluating suspended sediment and turbidity reduction projects in a glacially conditioned catchment through dynamic regression and fluvial process-based modelling

Elevated turbidity (T_n) and suspended sediment concentrations (SSC) during and following flood events can degrade water supply quality and aquatic ecosystem integrity. Streams draining glacially conditioned mountainous terrain, such as those in the Catskill Mountains of New York State, are particularly susceptible to high levels of T_n and SSC sourced from erosional contact with glacial-related sediment. This study forwards a novel approach to evaluate the effectiveness of stream restoration best management practices (BMPs) meant to reduce stream T_n and SSC, and demonstrates the approach within the Stony Clove sub-basin of the Catskills, a water supply source for New York City. The proposed approach is designed to isolate BMP effects from natural trends in T_n and SSC caused by trends in discharge and shifts in average T_n or SSC per unit discharge (Q) following large flood events. We develop Dynamic Linear Models (DLMs) to quantify how T_n-Q and SSC-Q relationships change over time at monitoring stations upstream and downstream of BMPs within the Stony Clove and in three other sub-basins without BMPs, providing observational evidence of BMP effectiveness. A process-based model, the River Erosion Model, is then developed to simulate natural, hydrology-driven SSC-Q dynamics in the Stony Clove sub-basin (absent of BMP effects). We use DLMs to compare the modelled and observed SSC-Q dynamics and isolate the influence of the BMPs. Results suggest that observed reductions in SSC and T_n in the Stony Clove sub-basin have been driven by a combination of declining streamflow and the installed BMPs, confirming the utility of the BMPs for the monitored hydrologic conditions.     

Greenhouse gas deposits in the deep sea

Gas hydrates are the largest deposits of hydrocarbons in the world. They are distributed throughout marine sediments and their stability depends largely upon temperature and pressure. Typically, ～99 percent of these hydrocarbon deposits are composed of methane, which is a potent greenhouse gas. Methane release from gas hydrates has been implicated in mass extinction events. Present and future changes in ocean temperature have the potential to increase the rate of methane production from gas hydrates and thus to affect Earth's climate. Whilst the deep sea normally serves as a sink for greenhouse gases, the release of methane from gas hydrates could be a hugely significant source in the future and pose a real threat to our efforts to limit greenhouse gas emissions.     

Some observations and characteristics of lightning ground discharges in southern Ontario

Abstract

Lightning ground flash and stroke observations were made with a single‐station gated, wideband magnetic direction‐finding system with a nominal range of 180 km located in Southern Ontario during the May‐September lightning‐active seasons of 1982 and 1983. Information was recorded on the azimuth of arrival, time, amplitude, stroke multiplicity and order, and polarity. The local climatology and seasonal statistics of lightning are analysed and summarized, and compared with standard observations of thunderstorm days and hours. Regional daily flashing rates and extremes for periods of 5 to 60 min were found to have a good empirical relationship. About 15% of the flashes had multiple strokes, generally less than 10 but with as many as 14 strokes. About 8% of the flashes were positive discharges; 3% of these were multistroke with no more than 2 strokes.

The lightning activity exhibits well defined diurnal peaks in the afternoon and at night 1–3 h before sunrise. The time interval between strokes was found to have a lognormal distribution with modal and median values of 60 and 75 ms, respectively, and no significant dependence on the order of stroke. The stroke‐to‐stroke amplitude changes within the same flash show that subsequent stroke amplitudes are often greater than the first. Subsequent strokes follow many patterns of change, the most common being an amplitude oscillating with ascending stroke order. The multistroke flash duration median values rose from about 80 ms for 2‐stroke flashes to about 650 ms for 8‐stroke flashes.

Under certain assumptions of system detection efficiency and range limits a regional ground flash density of 1.62 and 2.44 km^?2 a^?1 was estimated for the two years.