Hydraulic properties of the Paskapoo Formation in west-central Alberta

In an effort to better understand the hydraulic properties of the Paskapoo Formation, hydraulic conductivity and porosity were evaluated for a region in west-central Alberta. Whereas previous studies have focused mainly on sandstone units in the lower portion of the Paskapoo Formation, in southern and central parts of the province, this study focuses on the middle to upper portions. Hydraulic conductivity values were determined by air permeametry for seven drill cores from the area between Hinton and Fox Creek, Alberta. Thin-section petrology and porosity analyses using photomicrographs were also conducted for three of the seven drill cores. Results confirm previous findings that the Paskapoo Formation has heterogeneous hydraulic properties, with horizontal hydraulic conductivity values ranging from 10−10 to 10−5 m/s (determined by air permeametry) and porosity values ranging from 0.02% to 15.3%. The first measurements for the upper sandstone units are provided (1.1 × 10−9 – 2.6 × 10−5 m/s and 0.08%–15.3%) and numerous measurements of the middle siltstone–mudstone unit (1.1 × 10−10 – 4.9 × 10−8 m/s and 0.02%–1.8%) for the northwestern portion of the Paskapoo Formation. Qualitative petrologic analysis suggests that the degree of cementation, rather than grain size, is the dominant control on the hydraulic properties of this portion of the formation. This study determined primary hydraulic properties for both the highly conductive units often considered as aquifers and the low-conductivity units considered as aquitards or confining layers. When combined with previous findings, this study helps expand the understanding of the Paskapoo Formation and provides critical data for assessing groundwater resources.

A global-scale two-layer transient groundwater model: development and application to groundwater depletion

Groundwater is the world's largest accessible source of freshwater to satisfy human water needs. Moreover, groundwater buffers variable precipitation rates over time, thereby effectively sustaining river flows in times of droughts as well as evaporation in areas with shallow water tables. Lateral flows between basins can be a significant part of the basins water budget, but most global-scale hydrological models do not consider surface water-groundwater interactions and do not include a lateral groundwater flow component. In this study we simulate groundwater head fluctuation and groundwater storage changes in both confined and unconfined aquifer systems using a global-scale high-resolution (5 arc-minutes) groundwater model by deriving new estimates of the distribution and thickness of confining layers. Inclusion of confined aquifer systems (estimated 6 % to 20 % of the total aquifer area) changes timing and amplitude of head fluctuations, as well as flow paths and groundwater-surface water interactions rates. Also, timing and magnitude of groundwater head fluctuations are better estimated when confining layers are included. Groundwater flow paths within confining layers are shorter then paths in the underlying aquifer, while flows within the confined aquifer can get disconnected from the local drainage system due to the low conductivity of the confining layer. Lateral groundwater flows between basins are significant in the model, especially for areas with (partially) confined aquifers were long flow paths are simulated crossing catchment boundaries, thereby supporting water budgets of neighboring catchments or aquifer systems. The two-layer transient groundwater model is used to identify hotspots of groundwater depletion resulting in an estimated global groundwater depletion of 6700 km3 over the 1960–2010, consistent with estimates of previous studies.

Residence times and mixing of water in river banks: implications for recharge and groundwater–surface water exchange

Bank exchange processes within 50 m of the Tambo River, southeast Australia, have been investigated through the combined use of 3H and 14C. Groundwater residence times increase towards the Tambo River, which suggests the absence of significant bank storage. Major ion concentrations and δ2H and δ18O values of bank water also indicate that bank infiltration does not significantly impact groundwater chemistry under baseflow and post-flood conditions, suggesting that the gaining nature of the river may be driving the return of bank storage water back into the Tambo River within days of peak flood conditions. The covariance between 3H and 14C indicates the leakage and mixing between old (~17 200 years) groundwater from a semi-confined aquifer and younger groundwater (<100 years) near the river, where confining layers are less prevalent. It is likely that the upward infiltration of deeper groundwater from the semi-confined aquifer during flooding limits bank infiltration. Furthermore, the more saline deeper groundwater likely controls the geochemistry of water in the river bank, minimising the chemical impact that bank infiltration has in this setting. These processes, coupled with the strongly gaining nature of the Tambo River are likely to be the factors reducing the chemical impact of bank storage in this setting. This study illustrates the complex nature of river groundwater interactions and the potential downfall in assuming simple or idealised conditions when conducting hydrogeological studies.

Effect of Confining Layers of Steel Straps Confined High-Strength Concrete Cylinder under Uniaxial Cyclic Compression

The remarkable advantages and promising increment in concrete ultimate capacity as well as ductility by using steel straps as lateral confinement has brought the steel strapping tensioning technique (SSTT) as one of the most affordable confining technique in market. A number of studies have been reported the behaviour of SSTT-confined concrete under uniaxial monotonic compression loading but none of any study addressed the uniaxial cyclic response of such confinement. In this paper, twenty-one high-strength concrete cylinder specimens with diameter of 150 mm and 300 mm in height were cast, laterally pre-tensioned with steel strap in different confining layers and tested to failure under uniaxial cyclic and monotonic compression loading. A number of conclusions to be drawn from experimental results including the tangential validation of stress-strain curve for uniaxial monotonic and cyclic loading, independency of plastic strain to the amount of confining layers, the disagreement of uniqueness concept on the repeated uniaxial unloading and reloading cycles, and the promising effect of confining layers and loading patterns to the ultimate capacity of SSTT confinement. A plastic strain model is proposed and compared with existing plastic strain models. The result proved that SSTT confinement able to secure the lowest plastic strain among the others existing confinement method.

Residence times and mixing of water in river banks: implications for recharge and groundwater – surface water exchange

The residence time of groundwater within 50 m of the Tambo River, South East Australia, has been estimated through the combined use of 3H and 14C. Groundwater residence times increase towards the Tambo River which implies a gaining river system and not increasing bank storage with proximity to the Tambo River. Major ion concentrations and δ2H and δ18O values of bank water also indicate that bank infiltration does not significantly impact groundwater chemistry under baseflow and post-flood conditions, suggesting that the gaining nature of the river may be driving the return of bank storage water back into the Tambo River within days of peak flood conditions. The covariance between 3H and 14C indicates the leakage and mixing between old (~17 200 yr) groundwater from a semi-confined aquifer and younger groundwater (<100 yr) near the river where confining layers are less prevalent. The presence of this semi-confined aquifer has also been used to help explain the absence of bank storage, as rapid pressure propagation into the semi-confined aquifer during flooding will minimise bank infiltration. This study illustrates the complex nature of river groundwater interactions and the potential downfall in assuming simple or idealised conditions when conducting hydrogeological studies.