For millennia, the traditional form of irrigation was flood irrigation. This ranged from hauling buckets over miles to complex siphons extracting water from underground aquifers or nearby water sources. Ancient farmers would then use the collected water to "flood" the land through uncovered trenches or canals. Not every ancient civilization was successful at this, and poor drainage and salt management left hundreds of acres of soil permanently damaged.
Today, flood irrigation is still widely used throughout the United States. Around 36% of irrigated fields in the U.S. used a flood system in 2015. This is a cheap and relatively low-tech solution in places where mechanical assistance is harder to use. However, only around 40-60% of the water used in flood irrigation is utilized by the crops. Open canals allow evaporation and seepage if not sealed correctly. Channels made only out of the earth can also be broken down over time or develop holes through animal intervention. Historically, irrigation canals have ranged from simple trenches dug in the dirt to brick and stone aqueducts reaching several hundred feet high. We have greatly improved the technology and materials we can use in modern times, helping us build stronger canals that prevent seepage and excess water loss.
Lining an Irrigation Canal
- Clay: This is one of the oldest materials used to seal canals and is still a cheap and low-impact option today. The process of compacting clay to remove all the air bubbles is known as 'puddling.' This densely packs the clay, leaving a watertight, yet not highly reliable seal. Unfortunately, any clay spread too thin or not 'puddled' sufficiently can still lead to significant seepage.
- Rammed earth: This is another ancient method used to seal canals, involving trampling clay-heavy soil until a watertight seal forms. (Typically, soil with 60% clay content is necessary). In 'ramming' the earth, soil particles are pushed closer together, leaving less space for water to seep through. While effective for its ease and affordability, a significant amount of water is still lost.
- Brick and stone: Large bricks, slabs of stone, or shaped concrete can also be used to line the canal. These are sealed and anchored with mortar to prevent water from flowing. However, small cracks can form behind or under places that may be hard to close. Freezing and thawing during winter months or even minor earth movement from soil settling or nearby traffic can cause cracks to form.
- Concrete: This is one of the most popular materials used in lining canals. It's also one of the most expensive options and requires a lengthy installation process.
Because concrete is relatively porous, water still tends to permeate through. There are sealants for concrete, but this solution is not always plant-safe. Both concrete and sealants can leach minerals and chemicals into irrigation water meant to be used for crops. Geomembrane liners, such as BTL's AquaArmor series, are often used as a barrier between concrete slabs and the soil underneath. These are safe for crops and won't break down when exposed to chemicals like pesticides or fertilizer when used in drainage canals. An underlayment will also protect the concrete from reactive materials within the soil beneath, which may cause issues if allowed to come in contact with the concrete.
- Cast-in-situ: Usually, liquid concrete is poured into molds along the canal and allowed to flow to the bottom. Curing will take a few weeks before the trench is usable, and cracking is possible during this time.
- Shotcrete: In this method, powered cement mix is mixed with water and shot at extremely high pressures. This allows for a thinner and more even layer of concrete. However, small mistakes can easily cause leaks. This also requires specialized equipment and a trained operator.
- Precast concrete: This has the fastest installation time, as there's no need to wait for the concrete to cure. Precast concrete slabs are lowered into place and sealed with mortar. Moving soil or rising groundwater may damage concrete sections, though a quality liner would prevent this.
- Cement mortar: Occasionally, mortar on its own can be used to line smaller canals. This involves using small bricks or stone slabs to then seal together with the mortar.
- Soilcrete: A cheaper option involves mixing soil with a thin mixture of cement. This combination can be sprayed onto walls and floors like shotcrete but comes with a rougher surface. (This extra friction may reduce velocity, reducing the total capacity of the canal).
The most effective way to seal a canal against water loss and undesirable chemicals involves using a durable, plant-safe geomembrane liner. These can be fabricated from reinforced polyethylene (RPE) or a combination of both low-density polyethylene (LDPE) and high-density polyethylene (HDPE) materials. While these liners work great on their own as a primary seal for canals, they also perform exceptionally well when used with any of the above methods. Even clay and rammed earth can be used over your liner as ballast while protecting your liner from U.V. light. However, most of BTL's liners are U.V. resistant and durable enough not to require a ballast. BTL offers both styles of geomembrane liners, as well as a suite of experts and resources dedicated to helping you create perfect, watertight, reliable irrigation canals.
Advantages of an RPE Canal Liner:
- More resistant to Winter Damage: RPE's flexibility reduces the chance of cracks or rips developing during freezing and thawing cycles. Clay, cement, concrete, and mortar-based liners can all be seriously damaged during periods of cold. While HDPE liners don't offer as much protection from freeze damage as RPE, this is still an excellent solution in warmer areas.
- Light Weight: Installing a geomembrane liner doesn't require the equipment or labor that concrete trucks or high-pressure sprayers may need. The light material is easy to carry by hand (or with small machinery) and can be spread out and assembled much quicker than other lining methods.
- Lower Cost: A high-quality liner only costs a fraction of what it may cost to purchase and install large precast concrete slabs, mortared bricks, etc. Their durability means that repairs are needed less often, saving you money for years to come.
