Search Results (3)

Climate change and anthropogenic pressures are the main drivers of the quantitative and qualitative depletion of water bodies, worldwide. Nowadays, in many urban areas, discharging effluents from wastewater treatment plants (WWTPs) into surface water bodies is a management solution to face the problem of water scarcity and sustain environmental flows. Although this practice can cause some concerns in public opinion about possible ecological side-effects and impairment of quality on receiving streams, it is an important contribution to the environmental baseflow of ephemeral streams, but also to groundwater recharge, especially during dry seasons, and in semi-arid and arid regions. This latter occurs through losing reaches along the streambed, though many factors may affect the infiltration rate, such as spatial distribution of streambed sediments and bedrock or the presence of channel lining. Moving from such premises, this study focuses on the Canale Reale River, an effluent-fed stream located nearby the city of Brindisi on the south-eastern side of the Apulia Region, in Italy. The Canale Reale flows through the Torre Guaceto protected wetland, located along the Adriatic coast. It collects effluents from four WWTPs with wastewater contributing for about 16.5% of the annual volume of channel drainage (i.e., 3.82 Mm³ out of 23.02 Mm³ along its 50 km long course). Within the framework of a complex geological setting, the Canale Reale River crosses different lithologies, which implies different streambed infiltration conditions. Using the Reach Length Water Balance method (RLWB), the transmission losses between the watercourse and the underlying aquifers were investigated. Particularly, the method allowed for the estimation of a spatially-average value of the riverbed’s infiltration rate applicable to the whole river course as well as the minimum, average, and maximum potential transmission losses ($T{L}_P$) from the river to the underlying groundwater systems. Combining the estimated $T{L}_P$ values and the Flow Duration Curve (FDC) allowed for the inferring of the Transmission Loss Duration Curves (TLDC). Finally, the water volume infiltrating during an average hydrological year was estimated to be 6.25 Mm³, 61% of which was due to treated wastewater discharge. The results obtained confirm that the practice of increasing the river flow rates with WWTP effluents reduces the dry riverbed periods, with potential improvements to the river’s ecological sustainability and relevant enhancement of groundwater recharge. Full article

Oxygen distribution and uptake in the hyporheic zone regulate various redox-sensitive reactions and influence habitat conditions. Despite the fact that fine-grain sediments in streams and rivers are commonly in motion, most studies on biogeochemistry have focused on stagnant sediments. In order to evaluate the effect of bed form celerity on oxygen dynamics and uptake in sandy beds, we conducted experiments in a recirculating indoor flume. Oxygen distribution in the bed was measured under various celerities using 2D planar optodes. Bed morphodynamics were measured by a surface elevation sensor and time-lapse photography. Oxygenated zones in stationary beds had a conchoidal shape due to influx through the stoss side of the bed form, and upwelling anoxic water at the lee side. Increasing bed celerity resulted in the gradual disappearance of the upwelling anoxic zone and flattening of the interface between the oxic (moving fraction of the bed) and the anoxic zone (stationary fraction of the bed), as well as in a reduction of the volumetric oxygen uptake rates due shortened residence times in the hyporheic zone. These results suggest that including processes related to bed form migration are important for understanding the biogeochemistry of hyporheic zones. Full article

Particle travel length is one of the main dimensions of bedload and strongly influences river morpho-dynamics, particularly when exploring the interactions between sediment transport and channel morphology. This process has been traditionally studied by using tagged stones that allow tracking the movement experienced by individual grains during transport episodes. In this paper, we relate measured particle travel lengths to flow metrics and river channel parameters. First, we link the event-based bedload volumes to the active-layer dimensions, and the product between the average bedload rates and the duration of competent flows. We then hypothesize that travel length depends on channel width, surface grain-size, particle size, bed structure, flow strength, and duration of competent flow. The results from this approach are, subsequently, tested with a set of tracer observations from eight rivers that were available in the literature. The relationship between travel length and flow metrics was found to be statistically strong and has the potential to allow us to quantitatively assess the one-day dynamics of particles moving along streambeds. We also analyzed the influence of channel morphology and bed structure and identified morphological signatures for particle transport in gravel-bed rivers. Full article