How geosynthetics help ensure water quality for all
By providing the barrier function, geosynthetics, mainly geomembranes, are essential for the collection, transport, storage and distribution of fresh water for dams, canals, reservoirs and pipelines (Koerner et al. 2008). Korer et al. (2008) proposed a freshwater cycle based on geosynthetics that receives, transports, stores and distributes freshwater . The following subsections discuss the use of geosynthetics in these various applications and the maintenance of water quality.
A major application of geosynthetics is in dams, which are important because of their safety and environmental impacts (Heibaum et al. 2006; Koerner et al. 2008). Geomembranes have perhaps been the most significant innovation in hydraulic engineering in the last 50 years. Their use can avoid problems such as the lack of suitable local materials, and they can withstand an unlimited water column. Geomembranes are used worldwide to waterproof all types of dams: hydroelectric dams, concrete and masonry dams, roller-compacted concrete dams, etc. (Cazzuffi et al. 2010). You can visit and buy geomembrane products and tools for design and construction from Geonik website.
Over the life of the dam walls, the head concrete degrades, leading to a corresponding increase in leakage. Geomembranes are often used to rehabilitate old concrete dams, with geomembranes almost always being exposed ; They are rarely used in the construction of new concrete dams. Composite geomembranes, which combine a geomembrane and a geotextile, are the most common for such applications: the geomembrane performs the lining function and the geotextile reinforces the geomembrane, protects it from mechanical damage caused by irregularities in the support and provides drainage. behind the geomembrane (Cazzuffi et al .2010).
In a dam, geomembranes also improve the safety of the dam by reinforcing the revetment. They can be placed in two places: on the upstream slope (90% of cases, according to the ICOLD database) and/or in the body of the dam (10% of cases). Among the geomembranes laid at the top of the slope, 70% were covered and 30% left uncovered (Cazzuffi et al. 2010).
In the case of roller-compacted concrete dams, geomembranes are typically used in new construction, with the geomembrane typically covering the entire upstream side of the dam. The mass of concrete compacted with a roller ensures the stability of the dam and the waterproofing membrane in front of it ensures the watertightness of the structure. The geomembrane can be left exposed or covered (Cazzuffi et al. 2010).
Water conveyance through canals
Canals are used to transport many types of liquids, although fresh water is the most common (Koerner et al. 2017). An important aspect of water management is the distribution of water to farmers via irrigation canals, which are sometimes also used to transport water to be used as drinking water (Giroud and Plusquellec 2017).
Water is precious, so water loss and degradation must be avoided. To limit water loss, some canals are lined by covering the bottom and side slopes of the canal with a barrier. Geomembranes have not yet reached the same level of application in canals as in dams: currently most canals are lined with cement concrete (Giroud and Plusquellec 2017).
Data from irrigation canals around the world show that approximately one-third of water transported is ultimately used for irrigation, while two-thirds is lost through leakage, evaporation and canal operation ( Giroud and Plusquellec 2017). Measurements and analyzes show that leakage through a properly laid geomembrane soon after construction is at least ten times lower than with a well executed cement concrete liner. If a geomembrane is protected from damage during operation, degradation processes affecting all materials will not impair geomembrane leakage until the geomembrane actually fails. Given the superior performance of geomembranes in canals, many examples of existing cement concrete linings repaired with geomembranes are available (Giroud and Plusquellec 2017).
Pumping water through hydraulic tunnels
Water tunnels are primarily used to transport water, either pressurized or free-flowing, for use in power generation and/or water utilities. These tunnels can be lined to prevent water from escaping and also to prevent water and harmful chemicals from entering the structure itself. Water tunnels are usually lined with steel, cast-in-place concrete or shotcrete. Geomembrane systems can be used as waterproofing for new construction, as a cover, or in rehabilitation projects to repair damaged or leaking liners such as. B. an exposed solution. PVC has been used successfully in hydraulic tunnels as a barrier against water and gas ingress and has now become a key element in hydraulic tunnel design. The geomembrane must be backed by a drainage structure to collect and drain the water. This avoids inward acting external pressure, which can build up and eventually destroy the installation (Cazzuffi et al. 2012).
maintenance of water quality
Various polymers such as PE, PP, PVC and EPDM are used to manufacture geomembranes for hydraulic applications. Bitumen can also be used (Touze-Foltz et al. 2010). Additionally, a number of chemical compounds are used in the manufacturing process to ensure the durability of polymeric materials, whether geomembranes or other geosynthetics. Despite the low water solubility of these chemical compounds, studies show that prolonged contact between geosynthetics and a surrounding aqueous medium extracts them from the geosynthetics (Blanco et al. 2012a, 2012b; Farcas et al. 2012; Pons et al. 2012). Chemical compounds and their breakdown products are potential sources of pollution that can affect the surrounding ecosystem and harm public health. To overcome these phenomena, some geomembranes have been specifically designed to solve potability problems .
Geomembranes in reservoirs
Geomembranes are often used to line reservoirs or ponds (see Figure 9). The heart of a revetment system is of course the impermeable material (ie either a geomembrane or a GCL) (Poulain et al. 2012). Applying a waterproofing membrane directly to the substrate is generally not recommended. The purpose of water drainage under a liner is to prevent the accumulation of water from a pond, channel or reservoir and subsequent uplift of the geomembrane liner system due to counter – pressure from a high groundwater table. Under-sheet drainage can be implemented by installing gravel layers, gravel-filled drainage ditches or geostrips. Depending on the amount of water to be drained, perforated geotubes can supplement gravel-based drainage systems. An added benefit of draining water below the liner, particularly in retention ponds, is that the quantity and quality of water discharged can be monitored to detect leaks in the liner system.
Evacuation of gases from the pad can be just as important as evacuation of water. Where gaseous fermentation is possible, underlying gaseous drainage should be carried out, particularly where complete excavation of organic soil is not economically feasible.
Underlying gas and water drainage is often implemented as a single system, although modern designs now tend to separate these drains (Poulain et al. 2012).
Geosynthetic covers for reservoirs
There are many reasons to cover a fresh water tank, eg. to minimize evaporation, reduce cleaning maintenance, control algae growth, reduce chlorine consumption, avoid animal waste, improve safety and prevent intentional pollution (Koerner et al. 2008, Heibaum 2010). Floating geosynthetic covers can serve desired functions (Sadlier and Taylor 2002; Peggs 2008; Benedetti et al. 2009).
Blanco et al. (2017) mention Renz’s work covering tanks using a PE shade mesh inserted between polyamide cables anchored to the pool edge beam to create a “quasi-horizontal cover”. This construction is the basis of the current Spanish standard on the subject (Blanco et al. 2017).
Redón-Santafé et al. (2014) designed floating photovoltaic covers for water tanks lined with a geomembrane of floating PE modules that adjust to different water levels in the tank by tie rods and elastic ties (Figure 10b). These covers help reduce evaporation and also provide renewable electricity. Such a combination of photovoltaics also saves land that can be used for agriculture (Ferrer-Gisbert et al. 2013).
Protection of geomembranes in hydraulic applications
One of the best ways to prevent accelerated aging of geosynthetics, and geomembranes in particular, is to cover them to limit their exposure to environmental factors such as oxygen, UV rays and high temperatures. Lining layers not only serve this purpose, but also prevent damage to the lining caused by floating or transported solids (e.g. ice, wood), by vehicles or machinery (e.g. pumping stations mobile), by burrowing animals and plant roots, and by vandalism or accidental human intervention. Another purpose of liners is to prevent wind movement from lifting geomembrane liner systems (Poulain et al. 2012).
A common design is to protect the geomembrane with a geotextile and then cover the geosynthetic with a layer of granular material (IGS n.d.a.). Other common constructions are concrete covers, precast blocks or slabs, cast-in-place reinforced concrete layers or even shotcrete over geotextiles, interlocking concrete blocks, hinged concrete blocks, concrete slabs , geocells or geomatresses, or soil and rock protection (Cazzuffi et al 2010; Poulain et al. 2012).