Transverse and longitudinal fluid flow modelling in fractured porous media with non‐matching meshes

A new discrete fracture model is introduced to simulate the steady‐state fluid flow in discontinuous porous media. The formulation uses a multi‐layered approach to capture the effect of both longitudinal and transverse permeability of the discontinuities in the pressure distribution. The formulation allows the independent discretisation of mesh and discontinuities, which do not need to conform. Given that the formulation is developed at the element level, no additional degrees of freedom or special integration procedures are required for coupling the non‐conforming meshes. The proposed model is shown to be reliable regardless of the permeability of the discontinuity being higher or lower than the surrounding domain. Four numerical examples of increasing complexity are solved to demonstrate the efficiency and accuracy of the new technique when compared with results available in the literature. Results show that the proposed method can simulate the fluid pressure distribution in fractured porous media. Furthermore, a sensitivity analysis demonstrated the stability regarding the condition number for wide range values of the coupling parameter.     

Soil sealing and soil water content under no‐tillage and conventional tillage in irrigated corn: Effects on grain yield

The main objective of this research was to analyse the effect of soil management on soil sealing and on soil water content under contrasting tillage practices and its influence on corn yield. The experimental research was carried out in a field cultivated with irrigated corn differentiated into three zones representing a gradient of soil texture (Z1, Z2, and Z3, i.e., increasingly coarser). Two plots under different soil management practices (conventional intensive tillage, CT, and no‐tillage, NT) were selected in each zone. The susceptibility to sealing of each soil and the steady infiltration rates were evaluated in the laboratory subjecting the soils to rainfall simulation applied at an intensity of 25 mm h^?1. In addition, soil porosity under each treatment was quantified. Soil water content (0–90 cm depth) was determined gravimetrically at the beginning and the end of the growing cycle and at the surface (0–5 cm) during three growing seasons and continuously at two depths (5–15 and 50–60 cm) during the last growing cycle. Soil water content was simulated using the SIMPEL model, which was calibrated for the experimental conditions. Corn yield and above‐ground biomass were also analysed. Significant differences in soil sealing among zones, with decreasing soil sealing for coarser textures, and treatments were observed with infiltration rates that were near twice in NT than in CT, being the effect of soil cover significant in the reduction of soil detachment and soil losses. NT showed higher soil water content than CT, especially in the surface layers. Above‐ground biomass production was smaller in CT than in NT, and in the areas with higher sealing susceptibility was 30% to 45% smaller than in other zones, reaching the smallest values in Z1. A similar reduction in corn yield was observed between treatments being smaller in CT than in NT. No‐tillage has been confirmed as an effective technique that benefits soil physical properties as well as crop yields in relation to CT, being its impact greater in soils susceptible to sealing.     

Observations of canopy storage capacity and wet canopy evaporation in a humid boreal forest

Evaporation of intercepted rain by a canopy is an important component of evapotranspiration, particularly in the humid boreal forest, which is subject to frequent precipitation and where conifers have a large surface water storage capacity. Unfortunately, our knowledge of interception processes for this type of environment is limited by the many challenges associated with experimental monitoring of the canopy water balance. The objective of this study is to observe and estimate canopy storage capacity and wet canopy evaporation at the sub-daily and seasonal time scales in a humid boreal forest. This study relies on field-based estimates of rainfall interception and evapotranspiration partitioning at the Montmorency Forest, Québec, Canada (mean annual precipitation: 1600 mm, mean annual evapotranspiration: 550 mm), in two balsam fir-white birch forest stands. Evapotranspiration was monitored using eddy covariance sensors and sap flow systems, whereas rainfall interception was measured using 12 sets of throughfall and six stemflow collectors randomly placed inside six 400-m² plots. Changes in the amount of water stored on the canopy were also directly monitored using the stem compression method. The amount of water intercepted by the forest canopy was 11 ± 5% of the total rainfall during the snow-free (5 July–18 October) measurement periods of 2017 and 2018. The maximum canopy storage estimated from rainfall interception measurements was on average 1.6 ± 0.7 mm, though a higher value was found using the stem compression method (2.2 ± 1.6 mm). Taking the average of the two forest stands studied, evaporation of intercepted water represented 21 ± 8% of evapotranspiration, while the contribution of transpiration and understory evapotranspiration was 36 ± 9% and 18 ± 8%. The observations of each of the evapotranspiration terms underestimated the total evapotranspiration observed, so that 26 ± 12% of it was not attributed. These results highlight the importance to account for the evaporation of rain intercepted by humid boreal forests in hydrological models.     

Influences of upstream reservoir stratification and downstream tidal fluctuations on the summer thermal regime of a regulated coastal river

This study focused on the effects of upstream reservoir thermal dynamics and downstream tidal influences on temperatures in a 25-km reach of Alouette River (coastal British Columbia, Canada) below a control dam and upstream of its confluence with Pitt River. Temperature was monitored during summer 2013 using 25 sensors. Water was released from the reservoir through a low level outlet at approximately 2.7 m³ s⁻¹, except during late spring when a higher flow was released over the dam spillway. Temperature variations in the lowest section of Alouette River, and in the lower portion of a tributary, were distinct from those further upstream due to backwatering effects associated with a semi-diurnal tide, which can cause flow reversals in Pitt River. An internal seiche was identified in the reservoir during mid-summer that resulted in oscillating releases of warmer and cooler water with an amplitude of up to 6°C and a period of approximately 12 hr. Wavelet analysis and band-pass filtering indicated that the 12-hr signal declined in strength with downstream distance, but remained detectable about 15 km below the dam. In contrast, the 24-hr diel signal increased in strength with distance below the dam. Travel times computed via cross-correlation of the 12-hr signals with that at the low level outlet were within ±10% of those estimated from measured mean velocities. Lagrangian tracking of water parcels using the derived travel times indicated that the cooling effect of periodic releases of cold water during the seiching period persisted to the lower extent of the non-tidal reach. The tidally influenced locations experienced higher temperatures than those recorded in the non-tidal portion of Alouette River, although the relative roles of heating in the upstream tidal reach versus upstream advection of water associated with tide-driven flow reversals in Pitt River require further study.