Abstract-This research is concerned with studying the effect of installing a weir on dissolved oxygen (DO) concentrations in water at different water depths. The study was done using a laboratory flume to be under controlled conditions; i.e constant temperature and no pollution sources. Then a mathematical simulation part is done -using Streeter-Phelps equation-to the study to relate it to real life conditions and thus determine where is the best location to install a water treatment plant on a river. Although many studies were done on examining the effect of hydraulic structures on air entrainment in water, bubbles captures in water, rate of transfer of oxygen to the water, rarely was the direct effect of hydraulic structures on dissolved oxygen concentration values in water investigated. This study will be investigating the effect of broad crested trapezoidal weirs on the dissolved oxygen (DO) in water at different longitudinal stations along the same water streamline; as well as, at different water depths. The study was done on a flume in the hydraulics laboratory at the American University in Cairo. It was found that installing the weir increased the values of the DO in water (comparing its upstream side with the downstream side) by an average of 5.3% comparing all depths. It was also found that installing a weir on a river will result in shortening the time the DO takes to recover after a pollutant was dropped in a river by 39.5%.
As noted by several researchers, the Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile River is expected to have unfavorable consequences for downstream countries like Egypt and Sudan. To limit GERD's negative effects on downstream countries, its operation should be secure, and its upstream water level should be ideal. However, none of the studies carried out the ideal operating scenarios from the perspective of controlling the number of gate openings. Accordingly, this study evaluates the optimal operating scenarios of the GERD and its impact on downstream countries by adopting a mathematical model to analyze the number of gates that can be opened and the depth of opening during different filling years. The paper also presents an environmental impact assessment of some GERD significant factors during construction, filling, and operation, with the goal of developing a mitigation strategy. The results showed that opening 5 gates at 4.56 m over a 10-year filling period would be the safest, most accepted, and most advantageous for Ethiopia and downstream countries. Moreover, creating a water-saving management plan in Egypt to overcome GERD's negative impacts would cost 877 billion Egyptian pounds. Doi: 10.28991/CEJ-2022-08-09-011 Full Text: PDF
ABSTRACT:This research studies the impact of water level control structures on self-assimilative capacity of rivers and on fish habitat. Constructing a water level control structure in a river reach will alter its hydraulics as well as its water quality, thermal regime and fish habitat. A mathematical model is developed to simulate river hydraulics, water quality, temperature and fish habitat. Diurnal dissolved oxygen concentrations are investigated to show their impact on fish. A case of a Nile River reach was studied to investigate the impact of the existence of the Esna barrage on the water quality and fish in its upstream reach. The barrage has negative impacts on the upstream self-assimilative capacity of the rivers. The waste load that the river could absorb was only 54 % (at low flow) and 78 % (at high flow) of the entire load if no barrage was present. Including in the simulation of the effects of photosynthesis and respiration, the above mentioned percentages were raised to 54 % and 91 %, respectively. Although water level control structures have negative impacts on the upstream self-assimilative capacity of the rivers, they have positive effect on downstream dissolved oxygen concentrations due to reaeration that happens across them. Downstream dissolved oxygen concentration increased by 6 % from its upstream concentration value. The barrage has a positive effect on fish habitat in the upstream section. The weighted usable area of Tilapia fish is doubled in case of barrage existence. The barrage causes a slight decrease in water temperature that reaches an average of 0.13 degree in the month of June.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.