Reservoir Lining Systems: An Engineer's Guide

The four common reservoir lining options are compacted clay, geomembrane, concrete face and filter point grouted mattress. Choose by what the embankment needs: how much seepage is acceptable, whether rapid drawdown can occur, how much settlement to expect, and which materials are nearby. Clay suits sites with suitable clay close by. A geomembrane gives the tightest seal but needs protection. Filter point mattress suits faces exposed to drawdown and movement.

Reservoir lining design depends on the dam or embankment type, the fill material, the operating water-level regime and the consequences of seepage. A small farm reservoir in a clay-rich catchment may need nothing more than a compacted clay blanket. A concrete-faced rockfill dam on a remote site may call for a face slab or a geomembrane system. This guide covers the upstream face of earthfill and rockfill embankments, and it compares the options on seepage control, drawdown behavior, settlement tolerance and durability. It does not rank them on cost, because cost is set by site conditions and is addressed in its own section.

For canal lining, see canal lining and canal lining methods comparison. For reservoir slope protection where seepage control is not required, see slope protection for canals and reservoirs.

Why Does Reservoir Lining Matter?

Seepage through and under an embankment is a primary safety concern in dam engineering, because uncontrolled seepage can start internal erosion and piping, a recognized cause of embankment dam failure. A lining reduces seepage by putting a low-permeability barrier on the upstream face. It does not have to be perfectly tight. The aim is to reduce seepage to a level the embankment's internal drainage can manage without carrying fine soil, so turbid seepage is the warning sign that something is wrong. The acceptable seepage limit is a project decision set by the designer and the dam owner.

What Are the Four Main Reservoir Lining Systems?

1. Compacted Clay Blanket

An upstream blanket of compacted clay is the oldest and most widely used seepage control measure. It is durable and tends to self-heal small cracks, because clay swells. It needs suitable clay on or near the site, since hauling clay far makes it uneconomic, and it is not a standalone solution where the embankment has coarse or gap-graded material prone to internal erosion.

2. Geomembrane

A synthetic polymer sheet (HDPE, LLDPE or PVC) placed on the upstream face is effectively impermeable when its seams are properly welded. Uncovered, it is exposed to sunlight, wave action, ice and vandalism, so it is usually covered with soil, concrete or a mattress. Seam quality is critical, and seams should be tested against the project specification. Gas and water pressure beneath the sheet can lift it if there is no drainage path.

3. Concrete Face

Reinforced concrete slabs on the upstream slope of a rockfill dam, the concrete-faced rockfill dam (CFRD), are a well-established seepage control system. They need a uniform, well-compacted rockfill support and high construction quality, and they are sensitive to differential movement, because cracks and open joints leak. Concrete face construction is typically associated with larger dams, where the scale justifies the work.

4. Filter Point Grouted Mattress

Filter point grouted mattress is a fabric-formed concrete lining with filter openings at the cell intersections. The openings let water pass slowly, which equalizes pore pressure during drawdown and reduces uplift on the face. The facing is articulated and flexible, so it can follow some embankment settlement. Thickness is selected within a range of 75 to 200 mm, set by project design for the exposure and loading.

How Do the Four Systems Compare?

The table is qualitative. It describes how each system behaves, not a performance guarantee, and the right answer for a given dam comes from the designer's analysis.

Which Lining Suits Which Project?

Why Is Rapid Drawdown the Critical Design Case?

Rapid drawdown is a fall in reservoir level faster than pore pressure in the embankment can dissipate. The water that was holding the lining against the slope is gone, but the water in the embankment is still pushing outward. The net force on the lining reverses, which can lift or buckle a sealed lining.

A designer has three ways to deal with it: make the lining permeable enough to equalize pressure, anchor it against the uplift, or provide a drainage layer behind it so pressure cannot build. Filter point mattress uses the first route, with filter openings that let pressure equalize. The drawdown rate that can be accepted depends on the opening size and on embankment permeability, so a geotechnical engineer should check it for each site. See uplift and pore pressure behind revetments for the mechanism.

What Matters for Installation on Reservoir Embankments?

Installation follows the same slope procedure as canal lining, described in the slope protection guide, with two added points:

1. Water level: if the reservoir cannot be fully lowered, the upper slope is placed in the dry and the lower slope and toe are placed within the limits of the method statement. A program showing water level, working zone and crew deployment should be prepared in advance.
2. Toe cutoff: the lower edge must be anchored in a cutoff trench or tied into an existing plinth, to stop seepage undermining the mattress at the toe, which is a high-risk zone on any embankment.

What Drives the Cost of a Reservoir Lining?

This guide does not give a cost, because a lining cost cannot be separated from the site. The factors that move it are the same for every system. They are the area and slope length, subgrade preparation, access for equipment and whether the reservoir can be lowered, the filter or protection layer needed beneath or above the lining, the distance to clay, rock, aggregate and cement, the grout supply, shipping and logistics for imported materials, and the inspection and maintenance the owner will carry out. Compare options on a like-for-like basis, with the same design conditions, the same scope and the same inspection regime. HydroBase prices each project individually, so send the reservoir geometry and drawdown conditions for a project-specific quotation.

When Is Filter Point Grouted Mattress Not Suitable?

It is not suited as the sole lining where very low seepage is required, such as for contaminated water or chemical storage, because the filter openings pass a small flow by design. It is also not a replacement for a geotechnical review of the embankment where internal erosion is a concern. In those cases combine a geomembrane or other barrier with a mattress cover, and have the dam engineer review the whole section.

What to Confirm Before You Specify a Reservoir Lining

Start with the water. Record the operating level range, the fastest drawdown the outlet works can produce, including emergency lowering, and the wave exposure on each face. Those three facts decide whether pressure relief, anchorage or thickness governs, and a lining chosen without them is chosen blind.

Next, agree the seepage requirement as a stated limit between the dam owner and the designer, and write it into the specification as the acceptance basis. A lining that reduces seepage is not the same as one that stops it, and tender documents that blur the two draw bids for different products.

Then deal with the embankment. A geotechnical engineer should review the fill, the foundation and any history of turbid seepage before a lining is chosen, because a lining covers a face and does not repair internal erosion behind it. Ask whether the existing face needs repair or regrading first, and who carries that work.

Finally, fix the interfaces: the toe cutoff, the crest termination and the junctions with outlet structures and spillway walls. Leaks and failures tend to start at edges, so these details deserve drawings of their own. Agree how the lining will be inspected after the first drawdown and after large floods, and who keeps the records.

Preparing a Reservoir Lining Enquiry for HydroBase

Where a filter point grouted mattress is on the shortlist, gather the reservoir geometry, the water-level range, the drawdown conditions and the wave exposure the designer has derived, together with the drawings. Thickness is chosen within the 75 to 200 mm range from the design load on each face, and the designer makes the final selection.

Panels are produced at the factory in Inner Mongolia, China. Custom-size panels take 5 to 7 working days to produce, and stock sizes dispatch in 3 to 5 days. Pricing is by project. Send the package through the contact page and the engineering team replies within 48 hours.

Sources and Further Reading

Open each document to confirm its current edition and scope before you rely on it.

• FAO, Lining of Irrigation Canals: FAO publication on lining irrigation canals. Checked 2026-10-24 (link and title).
• FAO canal lining chapter: FAO chapter on canal lining. Checked 2026-10-24 (link and title).
• ICID, About the Commission: The International Commission on Irrigation and Drainage. Checked 2026-10-24 (link and title).
• Geosynthetic Institute specifications index: Index of GRI test and specification documents. Checked 2026-10-24 (link and title).
• ICOLD bulletins: List of ICOLD bulletins on dams. Checked 2026-10-24 (link and title).

Frequently Asked Questions

What is the best lining for a small farm reservoir?

Where suitable clay is available close to the site, a compacted clay blanket is often the practical choice. Where it is not, filter point grouted mattress is an option, because it needs no soil cover and tolerates variable subgrade. The decision should rest on a site investigation and the designer's seepage and stability analysis.

Can grouted mattress be used on an existing leaking reservoir?

Yes, it is used for rehabilitation. The existing face is inspected, repaired and prepared, then the mattress is placed and grouted over it. Whether seepage is reduced enough depends on the cause of the leak, so a designer should confirm that the leak is through the face and not through the embankment or foundation.

Does filter point grouted mattress stop seepage completely?

No. It reduces seepage, but the filter openings pass a small controlled flow so that pore pressure can equalize. Where near-zero seepage is needed, a geomembrane beneath a mattress cover provides the additional barrier, with the mattress protecting the membrane from sunlight and mechanical damage.

Why is a geomembrane usually covered?

Uncovered geomembranes are exposed to sunlight, wave action, ice and mechanical damage. A cover layer, such as soil, concrete or grouted mattress, protects the sheet. The cover also adds weight against wind uplift, and drainage behind the membrane has to be designed so water pressure cannot lift it.

What does a designer need to size a reservoir lining?

Embankment material and geometry, water-level range and expected drawdown rate, wave exposure, subgrade condition, seepage limits and the local availability of clay, rock and cement. With these the designer can check drawdown stability and select the lining and thickness for the project.

To discuss a lining, send your reservoir geometry, water-level range, drawdown conditions and drawings and the HydroBase engineering team will reply within 48 hours. Related pages: slope protection and grouted mattress.