It is tempting to leave a canal unlined when it’s a small branch that is only supplying irrigation water to distant fields. Yet, there are dozens of reasons that should deter you from simply cutting a ditch in the dirt and letting water flow through it. Even drainage ditches, on roadsides, can benefit greatly from being lined with geomembranes. So, naturally, it’s a requirement for larger canals carrying much more water on a daily basis. Even just installing a liner on an existing canal saves money. A study by the U.S. Bureau of Reclamation found that every dollar spent on maintenance, repairs, and replacement of canal liners results in the savings of ten to twelve dollars-worth of water. That’s a significant return on investment over the years. Here’s just some of the problems that occur when a canal is used without any kind of liner in place.
Low Water Velocity
The first and most serious issue facing unlined earthen canals is a lack of water velocity. Rough surfaces, heavy weed growth and capillary pressure greatly reduce the speed and total flow of the water in the canal. You also don’t want to increase the velocity of water in an unlined canal past 0.7 meters per second, because erosion undermines the stability of the canal walls by undercutting them with every gallon of water that passes the raw soil. Any liner material, even just gravel piled on shallow canal sides, will increase velocity and reduce erosion effects by some amount. Geomembrane liners offer much higher maximum velocity figures depending on the material you choose. By increasing total velocity, you can reduce total construction costs for the canal. This can be accomplished by shrinking its total size, since the increased flow delivers more water in a smaller space. Some materials, like brick and stone, still reduce water velocity significantly due to a rough surface texture. Smooth and even materials, like geomembranes and concrete liners, support high velocity flows for maximum output where the water is needed most. This also plays into water system design regarding the number and placement of pumps, potentially reducing the need for some energy-intensive equipment.
Weed Growth In and Around Canals
Unlined soil, that remains saturated by a steady flow of water, is the ideal environment for hundreds of different aquatic and semi-aquatic weeds. Plants can grow in, around, and through the walls and floor of the canal. While it’s usually fine to have vegetation growing near or even on the far banks of the canal, plants inside it compromise the stability and greatly reduce flow and velocity. Each underwater weed becomes a barrier the water must flow around to reach its destination. Lined canals resist weed growth with far less maintenance and chemical treatment than unlined trenches. Geomembranes are resilient and thick enough to resist root growth, but clay and rammed earth liners are often penetrated by sprouting seeds or roots pressing in from outside. Concrete liners can withstand weed growth best when paired with geomembranes to keep roots from coming through cracks that form with time.
Water Loss Through Seepage
The single biggest problem caused by unlined irrigation and drainage canals is water loss due to seepage. All soils are somewhat porous due to the gaps between individual soil particles. These spaces allow water to flow out and away. Every drop that seeps away from the canal results in water loss that can’t be directly reclaimed. While the water eventually enters the nearest waterway or water table, the process can take anywhere from days to years. Therefore, preventing seepage and making the most of every drop that is pumped or siphoned, is essential for drought-stricken areas where there’s a lot of pressure on existing water supplies.
Don’t underestimate the amount of seepage that occurs in an earthen unlined canal. Similar to unlined ponds, unlined canals can lose 50% of more of their water supply to seeping alone. This is due to the porosity of even the most clay-heavy soils and was determined by studies done by the U.S. Bureau of Reclamation. There’s no need to pay double, or more, for the right amount of water when you can save money just by ensuring almost every drop makes it to the fields or power generation station.
Seepage also creates many secondary negative effects. It’s a contributing factor to soil damage through anaerobic conditions, loss of stability that triggers collapses or landslides, and root rot of nearby plants if the soil doesn’t get to ever dry out. Water and soil pollution are also possible if drainage canals are unlined because water contaminates can escape. The water can carry oil, paint, or fertilizer residues which will disperse with the wicking water.
Soil Stability and Water Saturation
Another major secondary problem, caused by water seepage, is saturation of surrounding ground. Farm roads, near irrigation canals without liners, often become completely impassable due to thick and sinking mud or potholes that can’t be filled. Water constantly moving under the surface of the soil can create quicksand-like conditions that result in equipment and vehicles getting stuck and needing extraction. Fields are hard to work when they’re soft and unstable due to being over-saturated with water. It’s also not a great environment for plant growth unless your crops require flooding regularly. In order to control what soil is hydrated, and how much moisture it receives, you’ll need to line all canals in some way to prevent seepage.
Poor Water Capacity
All of the factors above combine to greatly limit the total capacity of a canal regardless of its size. It’s simply not safe to completely fill a canal because of the higher risk of erosion and overtopping. Drainage, storm water, flood control, and irrigation canals can all cause millions of dollars of damages when flood conditions cause them to rise above their walls and banks. Unlined canals are much more likely to flood as the surrounding soil becomes saturated and contributes even more water accumulation. Liners keep soil moisture from migrating into the canal and increasing flood conditions, in addition to preventing erosion collapses that further block the canal and spread water across a larger area. Lined canals can safely hold more water, both on a daily basis and during emergency situations.
Water Pollution and Soil Contamination
Drainage canals, collecting runoff mixed with contaminants, must prevent water from escaping into the surrounding soil. This water eventually reaches natural waterways and can greatly damage animal and plant life. Even irrigation canals often gather fertilizer or pesticide runoff during treatment periods and should be lined to control where those chemicals end up. Proper processing of waste or contaminated water is essential to keep agriculture and manufacturing safe for surrounding families and the environment. Geomembranes are a relatively affordable way to ensure local streams, creeks and valuable crop land remain free from contaminants.
Damage from Grazing Livestock and Wildlife
Thirsty animals, seeking a drink, are often drawn to irrigation canals since they’re located far from busy residential or industrial areas. Even relatively small animals, like raccoons, woodchucks and foxes, can do a lot of damage to the banks of an unlined canal. Cattle and other livestock that share grazing space with irrigation canals also tend to use it as a watering hole, churning up the wet soil and collapsing walls. Animals can also be hurt, and even drown in canals that are unlined, when the bank collapses unexpectedly or they slip in the mud. At a minimum, to keep animals from being injured or drowning, be sure to line your canal. Consider some kind of fencing if you’re running canals through pastures where livestock is likely to enter. This is especially important if the livestock has the potential of bringing contaminants along with them, like E. coli bacteria, which was a major contributor to the last few romaine lettuce recalls.
Siltation Blockages
Finally, lined canals are much less likely to lose volume and velocity or gather high levels of silt compared to unlined canals. If silt does gather after a flood or major rainstorm, it’s much easier to dredge and clean a lined canal without worrying about disturbing any soil on the sides or bottom of the canal. Dividing unwanted silt from the existing soil of the unlined canal requires a delicate touch, stretching out the dredging process significantly. Geomembranes and concrete liners won’t be damaged by vacuum and net tools that quickly remove sludge and silt for rapid maintenance when needed. Since lining a canal also increases its velocity, the water will also keep silt moving, so far less of it can settle at the bottom. Self-scouring canals won’t erode as long as they’re lined, but the same effect will undercut the sides of unlined trenches rapidly and lead to unstable shelf-like banks that suddenly collapse.
Lining canals with products like RPE geomembranes from BTL Liners prevents all of these problems and more. Check out our industry leading ArmorPro liner for a flexible, chemical resistant, impermeable barrier to keep your canals from eroding or leaking water.
