Numerical Canal Seepage Loss Evaluation for Different Lining and Crack Techniques in Arid and Semi-Arid Regions: A Case Study of the River Nile, Egypt

Owing to the potential negative impacts of climatic changes and the grand Ethiopian renaissance dam, water scarcity has become an urgent issue. Therefore, the Egyptian Ministry of Water Resources and Irrigation has started a national project of the lining and rehabilitation of canals, to reduce seepage losses and for efficient water resource management. This study presents a new approach for assessing three different lining and crack techniques for the Ismailia canal, the largest end of the river Nile, Egypt. A 2-D steady state seep/w numerical model was developed for the Ismailia canal section, in the stretch at 28.00–49.00 km. The amount of seepage was significantly dependent on the hydraulic characteristics of the liner material. The extraction from aquifers via wells also had a considerable impact on the seepage rate from the unlined canals; however, a lesser effect was present in the case of lined canals. The concrete liner revealed the highest efficiency, followed by the geomembrane liner, and then the bentonite liner; with almost 99%, 96%, and 54%, respectively, without extraction, and decreasing by 4% for bentonite and geomembrane liners during extraction; however, the concrete lining efficiency did not change considerably. Nevertheless, the efficiency dramatically decreased to 25%, regardless of the lining technique, in the case of deterioration of the liner material. The double effect of both deterioration of the liner material and extraction from the aquifer showed a 16% efficiency, irrespective of the utilized lining technique.

Design guidance for protection of geomembrane liners in landfill applications

A new method of evaluating strains and predicting required protection layers that are placed over geomembranes is developed based on the combined effects of the clay strength and stiffness and the cushioning effect of a nonwoven protection layer. Plots giving the required geotextile protection for a different maximum strains are presented for expected landfill pressures under 300 kPa for angular, 38 mm gravel placed above a geomembrane liner for both drained and undrained loading conditions of the clay. A similar plot is also given for tire derived aggregate placed above the liner for pressures under 500 kPa for undrained loading conditions. All tests were conducted at room temperature. For all cases, nonwoven geosynthetic protection layers with mass per unit areas (MUA) exceeding at least 1200 g/m2 were required to limit long term strains below current threshold levels, such as a 4% strain target as given by Rowe and Yu (2019). The MUA of the protection layer, for the particular aggregates and geomembranes tested, is dependent on the loading rate, water content relative to optimum, the silt content, and the activity of the clay below.

Using Geomembrane Liners to Reduce Seepage through the Base of Tailings Ponds—A Review and a Framework for Design Guidelines

Geomembranes are used worldwide as basin liners in tailings ponds to decrease the permeability of the foundation and prevent further transportation of harmful contaminants and contaminated water. However, leakage into the environment and damage to the geomembrane have been reported. This paper reviews available literature and recommendations on geomembrane structures for use as a basal liner in tailings ponds, and presents a framework to achieve early involvement and an integrated approach to geomembrane structure design. Cohesive planning guidelines or legislative directions for such structures are currently lacking in many countries, which often means that the structure guidelines for groundwater protection or landfill are applied when designing tailings storage facilities (TSF). Basin structure is generally unique to each mine but, based on the literature, in the majority of cases the structure has a single-composite liner. The type of liner system used depends mainly on the material to be used on top of the structure, local hydraulic pressure gradient, and climate conditions. More practical information and scientific knowledge on the use of base liners in various cases are needed. A sustainable approach could be risk-based design, where the life cycle of the basin is taken into consideration. To this end, this paper proposes geomembrane-lined tailings pond to be assessed as a stakeholder. Emphasis on this, early enough, can ensure critical factors for tailings ponds to be considered from the outset in the design of mines and reduces the environmental footprint of the mining industry. More holistic project management and early involvement and integration are recommended to improve construction quality during the entire life cycle of the pond. In the long term, use of dry stacking or other alternative methods should be encouraged, despite the higher costs for operators.