الفهرس 
Advantages and Limitations of RBF
Groundwater Flow and ModelingOnly 14 pages are availabe for public view
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Abstract
Egypt faces a great challenge of water poverty due to several reasons such as population increase, climate change, pollution of some water resources, and the impact of Grand Ethiopian Renaissance Dam (GERD), in addition to the economic challenges. The rapid increase in water demand requires urgent and economic solutions, especially in remote areas, where the costs are high to connect these areas to potable water. The high capital costs of conventional treatment plants do not allow the authorities to accommodate the rising water demand. In addition, the surface water and groundwater are getting more polluted with industrial, agricultural, and municipal inflows. This pollution constrains the ability to use these resources and achieve the maximum benefit of these resources. Thus, riverbank filtration (RBF) becomes a promising solution that offers potable water at a low cost. RBF is the process of extracting water from a river by pumping wells located adjacent to the river, where river water is purified through natural physical, biological & chemical filtration mechanisms including filtration, adsorption, biodegradation, chemical precipitation, and redox reactions. RBF is considered a green, sustainable, and economic technology. There are various factors affecting RBF efficiency; for instance; aquifer characteristics, river hydrology/hydraulics, site geometry, riverbed characteristics, water quality, and operation of RBF wells.
RBF is already located in several locations in Egypt, and there are much more potential locations. Numerical modeling is one of the most crucial methods that can be used to determine the efficiency of RBF system in a specific site. In this work, the Idrasiya RBF site, which contains three RBF units, in Beni Suef, was selected to apply a numerical model to study the effect of four design parameters on both river filtrate portion and travel time, assuming that the extracted water quality is improved by increasing the river filtrate portion. These parameters are; 1) the extraction rates of the RBF wells, 2) the number of operating wells, 3) the apart distance between wells and the river, and 4) the spacing between the wells.
A numerical model was constructed using Groundwater Modeling System (GMS) v. 10.3 by Aquaveo, which is a friendly graphical interface for MODFLOW by USGS, using both MODPATH and ZONEBUDGET. A sensitivity analysis was performed to test the aquifer response to the change of different parameters. This model was used to simulate the existing situation and three design scenarios with a total number of 68 sub-scenarios. The results of this study can be summarized as follows;
• The RBF technique is a promising technique to be implemented in the field under investigation. The percentage of river-infiltrated water in the overall abstracted water was high (> 74 percent) in all scenarios. The major recharge source of the aquifer was the river infiltration from Bahr Yusuf, while the infiltration from agriculture was very limited relative to the infiltration from the river.
• Based on the studied scenarios, the most significant design parameters on RBF process were the distance between the river and the well, and the pumping rate.
• Placing the RBF at a further distance at the river bank could prolong the infiltration time and increase the potentiality of converting the infiltration environment into anaerobic. In contrast, it was observed that the spacing between the RBF wells had a minor impact on the efficiency of the RBF technique.
• from a hydraulic perspective, constructing one well at distance of 10.5 m from the river, with a pumping rate equal to 60 l/s, produced the highest river filtrate portion (98%). from a water quality perspective, it would be required to investigate the relationship between the distance from the well to the river and water quality parameters.
• Two equations were developed to estimate the river filtrate portion and minimum travel time as functions of pumping rate and distance between the pumping well and the river. These equations can be used only for this site for future projects. This procedure can be used as a guideline for similar RBF projects.
Applying this study’s outcomes for future Holding Company for Water and Wastewater (HCWW) RBF projects requires taking into consideration that the optimum hydraulic design of RBF is site-specific. Both hydraulics and quality aspects must be taken into consideration, with the aid of numerical modeling for groundwater flow and contaminants transport, with sufficient data. Besides, RBF wells should be continuously operated to keep a higher river filtrate portion.
The added value of this study is that it focuses on RBF modeling, with respect to the hydraulics aspects, and their influence on RBF process, as there is a research gap in Egypt in this regard.