Lecture 19
Canal Linings
I. Reasons for Canal Lining
1.
Installing plastic canal
lining (courtesy R.W. Hill)
To save water (reduce
seepage)
2. To stabilize channel bed
and banks (reduce
erosion)
3. To avoid piping through
and under channel
banks
4. To decrease hydraulic
roughness (flow
resistance)
5. To promote movement, rather than deposition, of sediments
6. To avoid waterlogging of adjacent land
7. To control weed growth
8. To decrease maintenance costs and facilitate cleaning
9. To reduce excavation costs (when extant material is unsuitable)
10. To reduce movement of contaminated groundwater plumes
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The most common and (usually) most important reason is to reduce seepage
losses (and this may be for a variety of reasons)
The assumption that lining will solve seepage problems is often unfounded,
simply because poor maintenance practices (especially with concrete linings) will
allow cracking and panel failures, and tears and punctures in flexible membranes
Seepage losses from canals can be beneficial in that it helps recharge aquifers
and makes water accessible to possibly larger areas through groundwater
pumping. The extent of aquifers is more continuous than that of canals and
canal turnouts. But, pumping ($energy$) is usually necessary with groundwater,
unless perhaps you are downhill and there is an artesian condition (this is the
case in some places).
“Administrative losses” and over-deliveries can add up to a greater volume of
water than seepage in many cases (that means that canal lining is not always the
most promising approach to saving water in the distribution system)
Sometimes, only the bottom of a canal is lined when most of the seepage has
been found to be in the vertical direction
It may be advisable to perform soil compaction testing under concrete linings to
determine if steps need to be taken to avoid subsequent settlement of the canal
Lining to decrease maintenance costs can backfire (costs may actually increase)
Concrete pipe is an alternative to lined canals, but for large capacities the pipes
tend to cost more
Many billions of dollars have been spent world-wide during the past several
decades to line thousands of miles of canals
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II. Some Types of Lining and Costs
Type
Typical Costs
1. Soil
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Lime
Bentonite clay
“High-swell” Bentonite & coarse clay or other “bridging material”
Geosynthetic clay liner (“Bentomat”)
Soil mixed with portland cement
Thin compacted earth (6 - 12 inches)
Thick compacted earth (12 - 36 inches)
2. Fly Ash ............................................................................................... $3.00/yd2
3. Masonry (stone, rock, brick)
4. Concrete (portland cement)
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Nonreinforced concrete ........................................................... $5.00/yd2
Reinforced concrete (with steel)
Gunite, a.k.a. shotcrete, a.k.a. cement mortar (hand
or pneumatically applied; w/o steel reinforcement)................ $12.00/yd2
Gunite, a.k.a. shotcrete, a.k.a. cement mortar (hand
or pneumatically applied; w/ steel reinforcement).................. $15.00/yd2
5. Plastic
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Polyvinyl Chloride (PVC) ......................................................... $5.00/yd2
Oil Resistant PVC
Chlorinated Polyethylene (PE)
Low Density Polyethylene........................................................ $4.00/yd2
High Density Polyethylene..................................................... $10.00/yd2
Polyurethane foam with or without coatings
6. Asphalt (bituminous)
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Sprayed (“blown”) asphalt
Asphaltic Concrete .................................................................. $4.00/yd2
7. Synthetic Rubber
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Gary P. Merkley
Butyl Rubber............................................................................ $8.00/yd2
Neoprene Rubber
Shotcrete over geosynthetic .................................................. $37.00/yd2
Concrete over geosynthetic ................................................... $26.00/yd2
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III. Comments on Different Lining Materials
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Pneumatic application of shotcrete
The USBR has had a
long-standing research
program on canal lining
materials and
installation techniques
(began in 1946, but
essentially discontinued
in recent years)
There are many
publications with
laboratory and field
data, design guidelines
and standards, and
other relevant
information (but you have to dig it all up because it doesn’t come in one book)
Many technical articles can be found in the journals on canal lining materials,
construction methods, and experience with different types of linings
Earthen Linings
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Earthen linings usually require significant over-excavation, and transport of
suitable material (in large volumes) from another site
Many earthen linings are 2 - 3 ft thick; “thin” linings are 6 - 12 inches thick
Clay linings can crack after only a few cycles of wetting and drying, causing
increased seepage loss. Bentonite clay swells considerably when wet, but
cracks may not completely seal after the canal has been dried, then filled with
water again.
Bentonite is a special kind of clay, usually made of up decomposed volcanic ash,
and containing a high percentage of colloidal particles (less than 0.0001 cm in
diameter)
High-swell Bentonite may swell 8 to 12 times in volume when wetted; other types
may swell less than 8 times in volume
Bentonite disperses well when mixed with soft water, but may flocculate (clump
up) when mixed with hard water. Flocculation can be avoided by adding one or
more dispersing agents (e.g. tetrasodium pyrophosphate, sodium
tripolyphosphate, sodium hexametaphosphate). Low-swell Bentonite tends to
flocculate easier.
Repeated drying-wetting cycles can cause loss of lining density, loss of stability,
and progressive deterioration of the lining
Other than Bentonite, clay linings may be of montmorillonite, or montmorillonite chlorite
Some clay linings have been treated with lime to stabilize the material. The
addition of lime to expansive soils (e.g. Bentonite) improves workability and
increases structural strength
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Portland Concrete
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Small concrete-lined canals are
Rubber strip at panel joint
usually non-reinforced
Steel reinforcement (rebar or steel
mesh) is also not commonly used on
large canals anymore unless there
are compelling structural reasons
The elimination of steel reinforcement
from concrete canal linings saves
about 10 to 15% of the total cost
(USBR 1963)
During the past several years it has
become popular to install concrete
linings in small canals at the same
time as final excavation and finishing, often using a laser to control the alignment
and longitudinal slope
Some “underwater” concrete lining operations have been performed in recent
years on full canals (so as not to disrupt delivery operations)
Careful shaping, or finishing, of the native soil is an important step in the
preparation for concrete lining simply because it can greatly reduce the required
volume of concrete (significantly lowering the cost)
Manual concrete lining of a canal reach (every other panel is
poured first to facilitate formwork)
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Reinforced concrete can contain rebar and or wire mesh. Reinforcement is
usually for structural reasons, but also to control cracking of the lining
Concrete panel joints may have rubber strips to prevent seepage
Weep holes or flap valves are often installed in cut sections of a concrete-lined
canal to relieve back pressures which can cause failure of the lining
Flap valves may be installed both in side slopes and in the canal bed
Some concrete-lined canals have (measured) high seepage loss rates,
particularly in “fill” sections of canal, and in soils with high permeability (usually
sandy soils) -- but, seepage rates are rarely measured; they are “assumed”
based on tables in books
British researchers report that their investigations show that if 0.01% of the area
of a concrete canal lining is cracked (0.01% are cracks), the average seepage
rate may be the same as that of an unlined canal
Soil mixed with Portland cement, especially sandy soil, can be an acceptable
cost-saving approach to canal lining
IV. Concrete Lining Thickness
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Lining thickness is often chosen in a somewhat arbitrary manner, but based on
experience and judgment, and based on the performance of existing linings on
other canals
Thinner linings may crack, but this does not have to be a problem if the cracks
are sealed during routine maintenance (not all concrete-lined canals enjoy
routine maintenance)
Concrete lined channels often have high seepage loss rates due to cracks and
unsealed panel joints
Grooves are often specified to control the location and extent of cracking, which
can be expected even under the best conditions
The selection of lining thickness is an economic balance between cost and
durability (canals perceived to be very important will have more conservative
designs -- municipal supplies, for example)
The USBR has suggested the following guidelines:
Lining Type
Unreinforced concrete
Asphaltic concrete
Reinforced concrete
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Thickness (inch)
2.00
2.50
3.00
3.50
4.00
2.00
3.25
4.00
3.50
4.00
4.50
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Discharge (cfs)
0-200
200-500
500-1,500
1,500-3,500
> 3,500
0-200
200-1,500
> 1,500
0-500
500-2,000
> 2,000
Gary P. Merkley
Lining Type
Gunite (shotcrete)
Thickness (inch)
1.25
1.50
1.75
2.00
Discharge (cfs)
0-100
100-200
200-400
> 400
Plastic and Rubber
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Plastic linings are also referred to as “geomembranes” or “flexible membrane”
linings
Plastic canal linings have been in use for approximately 40 years
Plastic and rubber linings are covered with soil, soil and rock, bricks, concrete, or
other material for
1. protection
• ozone “attack” and UV radiation
• puncture due to maintenance machinery
and animal feet, etc.
• vandalism
2. anchoring
• flotation of the lining (high water table)
• resist gravity force along side slope
• wind loading
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Plastic linings are typically 10 to 20 mil (0.010 to 0.020 inches, or 0.25 to 0.5 mm)
-- thicker membranes are usually recommendable because of increased
durability, and because the overall installation costs only increase by about 15%
for a doubling in thickness
The USBR previously used 10 mil plastic linings, but later changed most
specifications to 20 mil linings
Plastic linings of as low as 8 mil (PE), and up to 100 mil have been used in
canals and retention ponds
Low density polyethylene (LDPE) is made of nearly the same material as
common trash bags (such as “Hefty” and “Glad” brands), but these trash bags
have a thickness of only 1.5 - 2 mils
Plastic canal linings are manufactured in rolls, 5 to 7 ft in width, then seamed
together in a factory or shop to create sheets or panels of up to 100 ft (or more)
in width
Rubber membrane linings can have a thickness ranging from 20 to 60 mil
Flexible plastic and synthetic rubber linings are susceptible to damage
(punctures, tears) both during and after installation
Flatter than normal side slopes (say 3:1) are sometimes preferred with plastic
linings to help prevent the possible migration of the lining down the slope, and to
help prevent uncovering of the lining by downward movement of soil
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Correctly installed plastic and synthetic rubber linings are completely impervious,
provided they have not been damaged, and provided that the flow level in the
channel does not exceed the height of the lining
Plastic liners will “age” and lose plasticizer, causing a loss of flexibility and
greater potential for damage. Increased plasticizer during fabrication has been
shown to be effective in this regard
plas-ti-ciz-er (plas'tuh sie zuhr) n. a group of substances that are used in plastics to
impart viscosity, flexibility, softness, or other properties to the finished product
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Some canals in central Utah have had plastic linings for more than 30 years, and
most of it is still in good condition (measured seepage is essentially zero in the
lined sections, but some evidence of puncture/tearing has been found)
Plastic lining material is sometimes used to retrofit existing concrete-lined canals
after the concrete lining canal fails and or continued maintenance is considered
infeasible
Preparing a canal section for buried
membrane lining (courtesy R.W. Hill)
In the former Soviet Union, thin PE lining has been placed under precast slabs of
concrete lining in some canals
In India, some canals have been lined with plastic (PE) on the bottom, and bricks
or tiles on the side slopes
Polyethylene (PE) is the lowest cost geomembrane material, PVC is next lowest.
Some newer materials such as polyolefin are more expensive
Exposed and Buried Membranes
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Exposed membrane linings have been tried, but tend to deteriorate quickly for
various reasons
Exposed membrane linings have recently been installed in some full (operating)
canals
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Gary P. Merkley
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Buried membrane lining should have a cover layer of soil of approximately 1/12th
of the water depth, plus 10 inches
Some vegetation can penetrate these types of linings (asphaltic too), so
sometimes soil sterilant is applied to the soil on the banks and bed before lining
Fly Ash
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Fly ash is a fine dust particulate material (roughly the size of silt) produced by
coal-burning power plants, usually in the form of glassy spheres
Fly ash contains mostly SiO2 (silicon dioxide), Al2O3 (aluminum oxide), and Fe2O3
(iron oxide)
Fly ash is often mixed with soil to form canal linings, the mixture being more
dense and less permeable than soil alone
Fly ash is sometimes mixed with both soil and portland cement
V. References & Bibliography
ASAE. 1994. Standards. Amer. Soc. Agric. Engr., St. Joseph, MI.
Davis, C.V. and K.E. Sorensen (eds.). 1969. Handbook of applied hydraulics. McGraw-Hill Book
Company, New York, N.Y.
Frobel, R.K. 2004. EPDM rubber lining system chosen to save valuable irrigation water. Proc. of the
USCID conference, October 13-15, Salt Lake City, UT.
USBR. 1968. Buried asphalt membrane canal lining. USBR research report No. 12, Denver Federal
Center, Denver, CO.
USBR. 1963. Linings for irrigation canals. USBR technical report, Denver, CO.
USBR. 1984. Performance of plastic canal linings. USBR technical report REC-ERC-84-1, Denver
Federal Center, Denver, CO.
USBR. 1971. Synthetic rubber canal lining. USBR technical report REC-ERC-71-22, Denver Federal
Center, Denver, CO.
USBR. 1986. Tests for soil-fly ash mixtures for soil stabilization and canal lining. USBR technical
report REC-ERC-86-9, Denver Federal Center, Denver, CO.
USBR. 1994. Water operation and maintenance. USBR technical bulletin No. 170, Denver Federal
Center, Denver, CO.
www.geo-synthetics.com
Gary P. Merkley
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