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Mining operations in the Northern Territory of Australia
Published in Tad S. Golosinski, Mining in the New Millennium Challenges and Opportunities, 2020
Acid mine drainage is a serious and chronic environmental mining problem in the Top End. Most of the Top End’s ore deposits are associated with elevated levels of sulfidic material, which oxidizes, producing acid, as it is exposed at the surface. The rate of acid generation is greatly affected by the rate of oxidation of pyrite which is in turn affected by high temperature. The rate of oxidation of pyrite can be so high that serious acid drainage can form in a very short time. The strongly seasonal environment exacerbates the problem, as weathering products, primarily from waste rock, accumulate during the dry season and are often transported off site in run-off from the first rains of the wet season. This gives rise to a “first flush” effect which can have definite impacts on the downstream environment, especially the aquatic system. Measures, such as selected placement and sealing of sulfidic material, must be implemented to prevent acid mine drainage.
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
A point source is a regulatory term meaning a source that is discharged through a pipe at a known position, whereas a nonpoint source originates from flow distributed over the land surface. To simplify matters, urban runoff is going to be considered a nonpoint source because it is a diffuse source of pollution and the flow follows the temporal and spatial characteristics of rainfall over a large area. If the concentration of the contaminant during a storm were constant, the mass versus time (loadograph) would match the hydrograph. What usually takes place is that the concentration versus time (pollutograph) exhibits a high concentration at the beginning of a storm; this is known as the first flush. The first flush is a phenomenon that is due to high rainfall intensities at the beginning of the storm creating higher runoff and larger sediment wash-off (due to buildup prior to runoff). The first flush can be readily seen in sewers where the solids were deposited during dry weather and washed away during the first storm event; it is less evident in highly urbanized areas where factors such as street cleaning, traffic, and wind remove the sediments just as fast as they are deposited. On pervious surfaces, buildup plays a lesser role, and entrainment of water quality constituents in runoff is due more to erosion and solution mechanisms. Constituents may be adsorbed onto particular matter and thus be subject to transport as solids [Huber, 1992].
Drainage
Published in Sarah Bell, Urban Water Sustainability, 2017
The concentration of pollutants in stormwater runoff is not uniform throughout a storm event. The ‘first flush’ rainfall event after a dry period is likely to have the highest concentration of pollutants as contaminants built up on surfaces or in drains are washed off or re-entrained in water flows in pipes and channels (Bertrand-Krajewski et al., 1998). Concentration of many contaminants typically peaks early in the storm event, declining rapidly as the pollutants are washed from the surface. Managing the first flush of contaminants is therefore an important goal for reducing pollution from surface water runoff. This can be achieved by diverting the first flush away from the receiving environment towards storage or treatment (Kayhanian and Stenstrom, 2005). Sediment contamination of runoff may continue to increase as a result of erosion in the catchment, from roadsides, building sites and in channels subject to high flow volumes and velocities. The quality of surface water and the risks of contamination are important considerations in designing drainage systems that aim to increase groundwater infiltration as the means of reducing runoff. Infiltration of contaminated surface water can contribute to pollution of groundwater, with long-term environmental consequences due to the difficulty of remediation and containment.
The N:P:Si stoichiometry as a predictor of ecosystem health: a watershed scale study with Ganga River, India
Published in International Journal of River Basin Management, 2019
Ekabal Siddiqui, Jitendra Pandey, Usha Pandey
Concentrations of DOC and nutrients in land surface runoff varied with land use (Figure 2). Differences in surface runoff variables were significant with respect to site (p < .05; ANOVA). We also tested if there are significant differences between first flush results and the mean values. Irrespective of land use, runoff concentrations of carbon and nutrients were significantly (p < .05) higher in first flush compared to their respective mean values in total runoff (Figure 2). First flush is characterized by disproportionately high delivery of pollutants during early part of land surface runoff events. Earlier studies have shown strong first flush effect influencing stream water quality and suggested its relevance over the mean values for designing runoff quality control facilities (Gikas and Tsihrintzis 2012, Hathaway et al2012, Chow and Yusop 2014).
Semi-probabilistic design of rainwater tanks: a case study in Northern Italy
Published in Urban Water Journal, 2018
G. Becciu, A. Raimondi, C. Dresti
Most common First Flush devices divert runoff until a fixed volume is reached. To guarantee that only clean water is destined to the tank, the diverter should be emptied between storms even if the fixed volume is not fully reached. Characteristics and amount of runoff pollution depend mainly on the duration of the antecedent dry weather period, the type of yielding surface, the rainfall intensity and duration. The part of runoff that should be intercepted and discarded depends also on the type of the intended use for harvested water.
Water end-uses and rainwater harvesting: a case study in Brazil
Published in Urban Water Journal, 2020
Gabriela Hammes, Enedir Ghisi, Liseane Padilha Thives
The first flush corresponds to the rainwater from the catchment area sufficient to carry dust, leaves and debris that may accumulate on the roof of the house. NBR 15527 (ABNT 2007) states that the amount of first flush must be calculated, but if there is no specific data, the Standard recommends discarding the first 2 mm of rainfall.