Digging a canal or ditch in the soil and running water through it without lining the bed is relatively inexpensive, and may be the solution for very temporary problems, such as immediate drainage from a flood area, or rapid filling of a pond from a water source. But for most other situations such as irrigation, water management or longer term installations, the initial saving from not installing a liner is greatly outweighed by the efficiencies of a lined canal, which conserves water, protects the soil and reduces maintenance.
A key study by the U.S. Bureau of Reclamation found that a canal lined with a geomembrane liner produced a 10 to 1 savings in costs, despite the initial investment. In other words, for every dollar spent on installing a proper liner for the canal, this returned a savings of at least ten dollars in water, soil and maintenance costs over a fairly short period of time. People had long thought this, and the Bureau finally made a study to demonstrate the waste involved with an unlined water transportation canal. Clearly, it makes sense to think about the actual losses and detriments from leaving a ditch or canal unlined.
The most apparent detriment of an unlined canal is seepage of the water being carried, into the surrounding soil. Astonishingly, up to 50% or even more of the water being transported can be lost this way. Not only does this waste costly water, it prevents half of your water from going where it’s supposed to. Furthermore, the water seeping into the soil produces its own problems, creating a water table close to the surface that becomes marshy, hard to work, dangerous for wildlife, a breeding ground for pests, and even a mire that can get a vehicle stuck. Additionally, any contaminants that may be captured by the water flow can be leached into the soil instead of carried to the final destination, where testing and remediation can occur.
A canal or ditch that’s lined, ideally with a geomembrane liner, increases the velocity of the flow of water, and this has several benefits. The water is less subject to loss through evaporation, remaining in the open air for less time. Given the cost of water for irrigation, a lined canal means that a greater portion of the water actually reaches its intended destination, promoting optimal crop growth and higher yields. And given the harm to the land from wastewater or flood water, moving it efficiently in a drainage ditch to its destination is always the goal.
Moving faster, the water in a lined ditch can help keep the canal clean from silt and other debris, minimizing the eventual cleaning and maintenance that will arise over time. And a geomembrane liner can be cleaned without damage, while separating debris or contaminants from a soil base will take more time and effort. Also, moving the water faster and more efficiently means a smaller ditch can be dug, saving cost from the very beginning. Even a concrete, stone or clay liner is better than no liner, but these materials will still produce a drag on water flow, and are permeable, which means some seepage. The ideal material for a canal is a geomembrane liner.
A canal liner inhibits the growth of unwanted vegetation along the canal bed and sides. An unlined channel is far more prone to vegetation growth, which can impede water flow, damage the banks of the ditch and require chemical treatments. A lined ditch will preserve its banks by resisting soil erosion, which is a constant concern with an unlined ditch, that can quickly degrade. Keeping the optimum shape and having sound banks means that a canal can handle water surges and flooding more readily, moving the flood water quickly away without saturating the surrounding area. And any water saturation already existing or forming in the surrounding soil is kept out of the channel by the liner. Many of the issues that arise with an unlined canal are hard to see or to measure immediately, but the conditions cited above show plenty of reasons for lining a canal, ideally with an impermeable geomembrane material – see our guide to the various materials suitable for a ditch or canal liner.