Rainwater collection and storage is one way that people in California—particularly farmers in this major food producing region—can mitigate low water supplies during the droughts that commonly affect this area. While there are many types of rainwater collection systems, including small-scale rain barrels all the way up to underground storage systems, one of the most effective ways to collect, divert and store rainwater is in ponds and canal systems. This is because ponds and canals are relatively easy to build, with low overhead and low maintenance concerns. They’re also capable of storing vast volumes of water, which is crucial for farmers and others who need more than tank or barrel capacity to keep functioning.
If reservoirs and canals are one of the chief ways to supplement water supplies, then that means the focus is on liners for these systems. There are a lot of options available—everything from concrete and clay to flexible geomembranes. Each has its own set of factors to consider. Here, we’ll discuss the many types of liners that are suitable for rainwater collection systems to help you discover the right type of liner for your operation.
Rigid Liner Systems
For the purposes of rainwater collection and diversion, there are really only two main types of rigid pond liners: Concrete and clay liners. Plastic pond liners also exist, but these are typically small, designed more than anything as an easy way for homeowners to add a pond to their backyard landscape. Their limited capacity and decorative shapes make other small-scale options—like rain barrels or tanks—more feasible for rainwater.
Concrete Liners
Concrete liners are quite common in irrigation and stormwater systems. One can use them to line ponds and basins, and they also work well for channels, too. Storm drains are typically built with concrete risers because the riser material needs to be sturdy enough to prevent vertical drain walls from collapsing in on themselves when water is flowing through them. For this reason, concrete is an essential material in many stormwater diversion systems.
However, as a liner for ponds and channels, things change a little bit. Concrete is an effective material, yes—but there are some drawbacks.
- Expense is one of them. Of all liner types available, concrete is the most expensive for building liners and canal systems. This is because not only do you need to excavate, but also purchase the concrete, and then pay for supplies to build forms plus labor to make sure the concrete is installed properly.
- Maintenance is another concern. Concrete will degrade and crack with time—and shifting soils can speed that process along. With concrete, you’ll likely end up doing more repairs than with most other types of liners.
- Concrete also loses water through seepage since it is a porous material. In a drought-stricken region where water supplies are extremely low, this loss of water may not be something you want to risk.
Clay Liners
This type of liner system involves excavating your reservoir or canals, then lining the walls of these facilities with clay. It’s another popular option that works well for this purpose. In some areas, it may be the most inexpensive of all options—but this largely depends on the region. Where clay is common, and transport costs are low, your costs should remain low. However, other areas have to import clay over longer distances, which drives costs up astronomically.
While clay is effective, like concrete, it also has some disadvantages, particularly when used in stormwater management.
- Clay liners can be easily undermined. Because of this, clay can cause a lot of problems in stormwater diversion ditches and irrigation channels. Flowing water over time will wash away the clay and cause the walls to collapse. This process speeds right along with the flowing water. If you’re diverting a rushing flow of water from a recent heavy storm, for example, clay-lined channels might sustain a lot of damage.
- Clay also allows weeds and plant life to grow, which can cause clogs in irrigation systems as well as damage to the walls of ponds and channels.
- Like concrete, clay liners will allow some water to seep into the surrounding soils, which is not optimal during periods of extreme drought where every gallon counts.
- Maintenance is a concern since you’ll need to work to prevent walls from being undermined. This becomes an even bigger concern should the liner develop a leak since it can be extremely difficult to locate leaks in a clay lined pond.
Flexible Liner Systems
Where flexible liner options are concerned, you’ll have quite a few more choices available to you. This includes things like reinforced polyethylene, high density polyethylene, polyvinyl chloride, and more. Many of them look very similar—and purport to function similarly, but there are some significant differences between each of these types of liners.
Here, we’ll discuss the many types available.
Reinforced Polyethylene
Where flexible liners are concerned, reinforced polyethylene (RPE) is perhaps the best option available. This is for a variety of reasons.
- It’s thinner and lighter than other flexible geomembranes. That means that it costs less to ship (often substantially less, since it can be folded or rolled such that it takes up less space on a freight truck). Weight is also a consideration when shipping by poundage. Because it’s thinner and lighter, it’s also much easier to work with, which means you’ll pay less on labor for installation.
- High flexibility means you will be less constrained where pond and canal contouring is concerned. This material forms easily around slopes and outcroppings.
- Despite being thinner and lighter than other geomembranes, RPE is tougher. This is because it features a reinforced design that allows it to be lightweight while also being highly tear resistant and puncture resistant.
- RPEs—particularly products like BTL Liners’ AquaArmor—are available with fish-safe and plant-safe ingredients. This is crucial not only for passing health and safety regulations in California, but also because it makes it easier for you to reuse collected stormwater. Since it does not leach chemicals into the water, the water will be safe to use on crops or to water livestock if it isn’t polluted with agricultural, industrial, or residential runoff.
- This is a low-cost liner, perhaps even the lowest cost of all available liner options. While clay may be somewhat cheaper to install if you don’t have to import clay over long distances, RPE makes up for the initial investment expense by providing a long-lasting, low maintenance product that won’t require much in the way of future expenses.
- Speaking of maintenance and longevity, RPE allows you to avoid many of the headaches associated with other types of liners. It is UV resistant, which means you won’t need to worry about replacement after only a few years of sun exposure—which is crucial in sunny climates like California’s. You’ll also spend less time and money locating and repairing leaks since it is a durable material.
- RPE is very customizable. You can have it produced in large rolls to minimize the number of seams in a larger reservoir, or to eliminate seams in a canal, or you can have it made in smaller pieces for smaller applications. It can also be heat-welded at the factory so that you don’t have to worry about doing the seams yourself or paying for labor to do it during the installation of the liner.
- RPE also offers installation flexibility in terms of seaming. Heat welding is one option—and it provides a nice leak-resistant seal anywhere seams are made. However, you can also use seam tape or adhesives to seal the seams, too.
Reinforced Polypropylene
Not to be confused with RPE, reinforced polypropylene (RPP) is a type of liner that offers extreme UV resistance. Because of this, it is often regarded as the only feasible choice for installations that cannot be covered and that will receive high levels of UV exposure.
It can be a good choice for drought mitigation systems in places like California but bear in mind that it isn’t the toughest material out there. It is often recommended that RPP be installed with an RPE underlayment to prevent leaks—especially in areas where chemical exposure or abrasive wearing will take place. Chemical exposure may not present much of a hazard in stormwater harvesting systems that aren’t collecting industrial or agricultural runoffs, but in systems that are designed to handle fast-flowing storm waters, abrasion can be a concern.
Another disadvantage to this material is that it is typically much more expensive than RPE and other polyethylene-based products—though the increased expense is typically worse at the small-scale end of the spectrum for things like backyard projects or small water harvesting ponds on smaller farms.
High Density Polyethylene
High density polyethylene (HDPE) is another flexible liner option that works well for certain types of ponds. Even though it is commonly used as a pond liner, it may not be the best choice for rainwater collection and detention. One advantage HDPE does have is that it is UV resistant, which helps protect the material against California sunshine.
However, pound for pound, HDPE isn’t quite as durable as RPE. In order to increase durability, manufacturers make it thicker. This means that it is much stiffer, which makes it more difficult to install, especially around contours. It also weighs a lot more, which increases shipping costs. HDPE does stand up to chemicals quite well—but then again, so does RPE for a similar price and fewer hassles in shipping and installation.
Low Density Polyethylene
Low density polyethylene (LDPE) is similar to HDPE, but there are some differences. This material is lighter and thinner than HDPE, which makes it easier to install around contours and cheaper to ship to the site. This is mainly a tradeoff, however. LDPE may be lighter and more flexible, but it doesn’t feature the tear and puncture resistance of HDPE—and that is critical in stormwater systems where debris carried by rushing water could do damage, or where annual cleaning may be necessary.
In addition to that, LDPE does not feature as much UV resistance as other materials. This means it will degrade a lot more rapidly than UV resistant materials, especially in places like California that receive lots of sunlight.
Overall, RPE liners win out over LDPE because they do give you that crucial UV resistance, they feature the weight and flexibility you need for reduced shipping costs and ease of installation—and they have the toughness that LDPE does not have to help prevent leaks and tears. In general, LDPE liners are best used as a secondary barrier beneath concrete or another liner type.
Ethylene Propylene Diene Monomer
Ethylene propylene diene monomer (EPDM) is basically sheet rubber. That makes it quite a lot different from any other type of pond liner. Originally, EPDM started as a roofing product—and it is still quite popular as such. However, people have also adapted this material for use as a pond liner.
In fact, for a long time, EPDM was the only widely available flexible liner suitable for use in creating ponds. Despite this, that doesn’t make it an ideal choice. Today, there are too many other alternatives available to really justify the use of EPDM.
What makes EPDM an inferior choice? To start with, it’s very thick and heavy. Actually, to create a product with enough durability and tear resistance to be used as a pond liner, EPDM is manufactured to be thicker and heavier than any other geomembrane choice. That means hefty shipping fees to have it delivered, plus it is extremely difficult to work with. People struggle to unfold it and spread it, and when it comes to working with curves and contours, it tends to not form around them all that well.
Another issue with installation is that there is a lack of options when it comes to handling seams. With other liners, you may be able to use heat sealing or some sort of adhesive, but with EPDM, you must use a seam tape. Seam tape takes a lot of time to install, and it creates weak points that are more prone to leaking than other kinds of seaming.
On top of that, EPDM is a petrol-based product that isn’t noted for being fish or plant safe. It can leach harmful chemicals into the water—and that isn’t a good thing for Californians who are planning to collect and store rainwater for later irrigation use or to water livestock.
Polyvinyl Chloride
Polyvinyl chloride (PVC) is a liner choice that you will find quite often. In fact, it is one of the most commonly used liners available. Even so, it has quite a few issues that make it a less than ideal choice for stormwater management, diversion, and irrigation.
- PVC is the least durable of all available options. It doesn’t feature the tear and puncture resistance of even LDPE, let alone RPE, which is an incredibly durable material.
- Surprisingly, despite its lack of durability, PVC is a heavy material. Here again, this increases shipping costs, and it makes it much more difficult to install the liner.
- In terms of safety, PVC is on par with EPDM. It is known to leach chemicals into the water that harm fish and plants alike—and that makes it an unsafe choice for stormwater that is to become water for crops or livestock.
- PVC is also not UV resistant. Of all liner choices out there, this is the one that breaks down the fastest under heavy UV exposure. That leads to problems in places like California where sunshine is almost constant, and shade is quite rare.
When building a rainwater harvesting and preservation system using lined ponds and canals, the best choice for liners is clear. RPE outperforms all other liner choices—and it does it for a reasonable cost while offering a long-lasting product that doesn’t require the maintenance that comes with other options. It’s also fish and plant safe, which makes it easier to reuse collected rainwater in irrigation systems, or to create dual-purpose rainwater detention reservoirs that double as recreational venues.
