PERFORMANCE OF SOME CANAL AND DUGOUT

LININGS ON THE CANADIAN PRAIRIES *

K. PohjakasMember C.S.A.E.

Canada Department of Agriculture,Research Station

Swift Current, Saskatchewan

by

E. RappMember C.S.A.E.

Canada Department of Agriculture,Research Station

Lethbridge, Alberta

INTRODUCTION

The control of seepage from irrigation canals and dugouts to conservewater and to protect arable lands isan important consideration on the Canadian Prairies. Seepage from unlinedirrigation conveyance systems and dugouts wastes valuable water, and oftencauses adjacent lands to be unproductive because of waterlogging and saltaccumulation. This may necessitate theconstruction of expensive drainagesystems for reclamation.

One way to save water and reduceseepage is to make certain that conveyance systems and storage reservoirs areas watertight as it is economically feasible to make them. Lining with relatively impervious materials seems bestto meet this requirement.

In the early 1950s the Prairie FarmRehabilitation Administration (PFRA)became increasingly concerned aboutwater losses from canals and dugoutsand the damage caused by seepage toagricultural lands and other property.The Soil Mechanics Division of thePFRA was given the responsibility ofstudying and reporting on the suitability of canal linings previously installed by the PFRA. At the same time,the Drainage Division of the PFRAwas to conduct studies on water lossfrom existing canals, to recommendwhere linings should be placed, and toevaluate their effectiveness.

Progress reports (1, 2, 3) on thestudies were issued from time to time.The first includes reports on all liningsinstalled by the PFRA before December 1950. The second describes anddiscusses linings installed from December 1951, and includes a brief summary of observations on the performance of linings placed prior toDecember 1951. The third gives considerable detail on linings installedfrom December 1951 to December1956, and includes observations on theperformance of most of the otherlinings installed by the PFRA since theexperimental canal and dugout lining

58

program began. The program has beeninactive since 1956 and no further re

ports have been issued.

This paper reports on the effectiveness and permanence of particular lining materials, some of which are included in the original program andothers that have been installed in theinterim.

MATERIALS AND METHODS

The lining materials evaluated arecompacted earth, asphalt, concrete,and plastics. They represent the typesof linings most commonly placed incanals and dugouts in recent years. Instudying such linings the three majorconsiderations were watertightness,durability, and the initial costs. Water-tightness and cost are easily determinedbut the durability of these linings isstill questionable, particularly underthe severe climatic conditions encoun

tered on the Canadian Prairies.

The rate of seepage from a canal wasdetermined by the ponding method inwhich a section of canal is isolated bywatertight checks at both ends and thesection filled with water. With no

inflow or outflow the rate of water lossfrom either a ponded section of canalor a dugout during any given periodcan be measured by staff gauges, withcorrection being made for evaporationlosses. With data on the amount ofdrop in water level and on the dimensions of the ponded section, the seepageloss in cubic feet (f) per square foot(f) of wetted area per 24 hours maybe computed. Measurement of the dropin level of the water surface in feet per24 hours was used to express the rateof seepage. Experience has shown thatthe water surface drop per 24 hoursapproximates the calculated loss in ft8/ft2 per 24 hours.

Exposed black polyethylene plasticlinings have been used temporarily onthe Prairies for specific purposes, butbecause they were not considered to bepermanent installations data on themhave not been included in table IV.

Black polyethylene plastic linings werefirst installed at Swift Current projectsin 1955 to reduce seepage in areaswhere water losses were excessive; insome cases they replaced compactedearth linings. Earlier installations used8-mil plastic but more recently 6-milplastic has been used. Plastic liningsused were the required width for allsmall- and medium-size canals so that

only one transverse field joint wasneeded for each folded section of thelining ranging in length from 100 to200 feet. The standard installationpractice allowed 1 foot of freeboardabove the full supply level (FSL) andanother 1 to 1V2 feet of the lining wasrequired on both banks for anchoring.This was accomplished by excavatinga narrow ditch about 1 foot above theFSL, and burying the outside edges ofthe plastic sheet in the ditch bank toprevent the plastic from sliding downthe slope. Ditch banks were previouslygraded to a slope not exceeding 3 to 1,all sharp objects were removed byraking, and the finished surface wasrolled smooth. The linings were covered either with the material excavatedfrom the ditch or with sand and gravelhauled to the site. The exposed gravelsurface provided better erosion control,but was more costly because of thetransportation expense (figure 3).

Data on a large number of liningswere collected, but only those that contain seepage or cost figures are presented (tables I to IV).

RESULTS AND DISCUSSION

Compacted Earth

All linings were installed in canalsat locations where seepage rates hadbeen high and saline and alkaline conditions had developed below the canals.Most of these lined sections passedthrough sand and gravel lenses mixedwith less permeable materials. Seepagelosses from canals lined with compacted earth on the Bow River, Eastend,Maple Creek, and Swift Current projects are presented in table I.

CANADIAN AGRICULTURAL ENGINEERING, JAN. 1967

The ponding tests after the completion of lining showed that seepage wasreduced to a low rate in all cases studied. There is a gradual increase inseepage rates with time, as measured inthe* Eastend "G" lateral which waslosing water at a rather high rate after5 years. The Swift Current main canallining became more permeable eachyear after the lining was completed andafter 10 years had lost its effectiveness.

Compacted earth linings in othercanals deteriorated, but several werestill moderately effective 10 years afterinstallation. Freezing, thawing, and alternate wet and dry cycles have had adetrimental effect on the compactedearth linings. Each cycle tends to reduce the density of the original compaction (3). Linings less than one footthick, as installed in the Eastend "G"lateral, became pervious much fasterthan those one foot or more in thickness.

The unit cost of lining is higher forsmall ditches than for large canals. Theuse of standard earth-moving machinesemployed to line small ditches of lessthan 8-foot bottom width increasedthe unit cost considerably. The costwas considerably higher than that ofa standard blanket clay lining wherethe entire transverse section of canalhad been filled with impervious material and compacted before the finalcanal section was excavated. Standardblanket linings consist of clay materialthat is hauled to the over-excavatedcanal and compacted on the bottomand the sides to form a watertightlining. The availability of suitable clayand its distance from the canal influenced costs considerably.

The unit cost of lining smallerditches with compacted earth was asexpensive as that of lining them withplastic sheets (tables I and IV). Forlarger canals the cost of compactedearth linings compared favourably withthat of other lining materals. Experience in lining canals with clay hasshown that the minimum seepage lossobtained with the best clay lining isless than 0.10 foot per day (4), withan average of 0.20 foot per day, anda maximum 0.50 foot per day (5).

Asphalt Linings

Seepage losses from asphalt linedcanals and from a dugout are listed intable II. As all the linings listed havebeen in place since 1949 to 1951, afair assessment of their life expectancywas obtained. Asphalt linings were in-

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TABLE H. LINING COSTS AND SEEPAGE LOSSES FROM CANALS AND DUGOUTS

BEFORE AND AFTER LINING WITH ASPHALT

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canalSoil type

Type oflining

Year

lined

Cost persq yard

Seepage losses: rate in ft per day

Remarksstructure

Beforelining

Afterlining

Seepage losses(No. of years

since installation)

Swift CurrentMain Canal

Swift CurrentMain Canal

Swift Current"A" Lateral

Swift Current"A" Lateral

Melfort WaterStorage Dugout

Stn. 14+00 to 45+00

Stn. 80+00 to 104 + 82

Stn. 13+00 to 15 + 74

Stn. 44+00 to 45 + 64

Melfort ResearchStation

Clay, silt andsand

Clay, silt andsand

Silty clayand sand

Silty clayand sand

Sand lensesin clay bottom

Catalyticallyblown asphaltWW thickcovered with 8" of

soil

Catalyticallyblown asphalt Wthick covered with8" of soil

Asphalt impregnatedcotton and soilcover

Catalyticallyblown asphalton l"-2" aggregate,no cover

Catalyticallyblown asphalt, nocover

1949

1950

1950

1951

1951

$0.82

$1.09

$1.40

$2.40

$1.12

0.22

0.30

high

0.06

0.03

0.42

0.08

high

0.12 (7)

0.11 (6)

No seepage control

0.17 (14)

1.6 (2)

Effective after 16years

Effective after 15years

Not effective, lininghad decomposedafter 5 years

Effective after 14years

Not effective, wasrelined withplastic

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sure, caused by a high water table inthe early spring, was ruptured. However, a lining held down by the weightof a protective covering or water is lesssubject to damage by an upward hydrostatic force.

Concrete Linings

Results of tests with concrete linings(table III) were all obtained from the"A" lateral at the Swift Current Experimental Station. The linings hadbeen installed in 1950 to test the effectiveness of pneumatically appliedconcrete of different thicknesses, andthe effects of reinforcing and air en-trainment on the durability of concretelinings (figure 2a). Most of the concrete lined section of the "A" lateralwas in a cut, and seepage losses previous to lining were not very great. Alining placed in a canal passing througha cut is subject to more frost heavingbecause of the difficulty of draining thecanal before freeze-up. A lVS2-inchthick unreinforced section containednumerous, thick transverse and longitudinal cracks from which weeds grew(figure 2b). Its effect on seepage control was limited.

A 1 Va-inch thick reinforced concretelining contained intermittent longitudinal cracks about 1 foot from thebottom on both sides. There were afew hairline transverse cracks in thissection (figure 2c). Seepage rates haveincreased since 1953 but the liningwas still effective in 1965. A 3-inchthick unreinforced section containedVi- to 1-inch wide longitudinal cracksin the middle of both sides. Some topsections of lining had broken off andshowed evidence of frost heaving.There were numerous V&-inch widetransverse cracks throughout the section but the lining was still controllingseepage. The most effective lining wasa 2-inch thick reinforced section (figure 2d). On the south bank smallpieces of lining were broken off apparently by cattle but the rest of thelining was in good condition and showed no evidence of cracks or weedgrowth. Ponding tests showed that theseepage loss was the lowest in thissection.

In summary, the presence or absenceof reinforcing steel was more important than the thickness of concrete. Airentrainment also appeared to have littleinfluence on the durability of concrete.The reinforced IVi-inch thick sectionwas in much better condition than theunreinforced 3-inch section which costalmost twice as much as the thinner

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TABLE IV. LINING COSTS AND SEEPAGE LOSSES BEFORE AND AFTER LINING

WITH POLYETHYLENE BLACK PLASTIC

Project and Portion of

canalSoil type Type of

liningYear

lined

Cost per

sq yard

Seepage losses: rate in ft per day

structureBeforelining

Afterlining

Seepage losses(No. of years

since installation)

Bow River"F" Lateral

Stn. 175+00 to 197 + 25 Loam on sand

and gravel

6 mil plastic,soil and gravel

cover

1962 $1.40 0.20*—

0.0025 (3) Very effective after3 years

Bow RiverF-5 Lateral

Stn. 11+00 to 28 + 74 Loam on sand

and gravel

6 mil plastic,soil and gravelcover

1962 $1.40 2.06—

0.021 (4) Very effective after4 years

Bow River

F-5 Lateral

Stn. 28+74 to 49 + 00 Loam on sand

and gravel

6 mil plastic,soil and gravelcover

1962 $1.40 2.03—

0.16 (4) Effective lining after4 years

Swift Current

Main CanalStn. 45+00 to 80 + 00 Clay, silt and

sand

6 mil plastic,12" sand and

gravel cover

1963 $0.99 high—

No evidence of

seepage 2 yearslater

Effective lining

Eastend "B"

Lateral

Stn. 195+55 to 248 + 57and 147+00 to 153 + 00

Clay, sand and

gravel

6 mil plasticsand and gravelcover

1964 $0.67 high No evidence of

seepage 2 years

later

Effective lining

Bow River

Substation

Dugout

SE 4-13-16-W4 Loam on sand

and gravel

8 mil plasticsoil and gravelcover

1956 0.016 0.011 (9) Effective after 9

years

Bow River

Grover Dugout

SW 3-13-16-W4 Permeable topsoil on clay

8 mil plasticsoil and gravelcover

1955 $0.67 -— 0.015 0.013 (10) Effective after 10

years

Outlook Pre-

developmentFarm

Loam with

sandy subsoil

8 mil plastic,soil cover

1955 $0.48 high Lining rupturedafter 2 years

Original side slopeswere too steep.

Slopes wereflattened and a

new lining wasplaced 10 yearslater

*10 years before the lining was installed.

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reinforced section. Therefore, therewere definite economic advantages inusing reinforced concrete canal liningsat Swift Current.

Plastic Linings

Data on plastic linings (table IV)were obtained from the Bow Riverproject in Alberta, and from the SwiftCurrent and Eastend projects in Saskatchewan.

All listed linings except the one usedin the original Outlook Predevelop-ment Farm dugout, effectively controlled seepage losses. The lining in theOutlook dugout was damaged by thesloughing of side slopes and a newlining was installed after the side slopeswere changed.

Figure 3. Swift Current main irrigation canal 2 yearsafter 6 mil plastic was installed and covered with

12 inches of sand and gravel.

The majority of plastic linings havebeen performing well. The life expectancy of covered black polyethyleneplastic is estimated to be 20 to 30years. Where seepage rates have increased since installation, they havebzen traced to damage to the plasticlining caused either by animals or unstable side slopes. The cost of liningsmaller canals with plastic comparedfavourably with that of compactedearth linings and the plastic lining appears to be more durable. Where localsoil was suitable for covering the plastic lining, the unit cost was the lowestof any lining.

SUMMARY

The best seepage control was recorded with black polyethylene plasticlinings where the water loss was between 0.0025 and 0.16 foot per day.Asphalt and concrete linings followedand were from 0.06 to 0.19 and from

0.06 to 0.34 feet per day, respectively.Compacted earth linings were the leastwatertight in this group with lossesfrom 0.08 to 0.47 feet per day. Concrete linings were most costly, followedby asphalt, plastic and compactedearth.

CANADIAN AGRICULTURAL ENGINEERING. JAN. 1967

The durability of several linings wasobviously longer than the 15 to 16-yearobservation period. The initial goodseepage control of compacted earthlinings deteriorated relatively quicklyand most linings become gradually lesseffective. Compacted earth linings werein most cases definitely more perviousand had a shorter life span than theothers. Frost heaving caused mostdamage to concrete linings, particularlyin unreinforced sections where seepagelosses have increased steadily since installation. The earliest plastic lininginstallations dated back 10 years andsince that time no increase in seepagerates has been observed.

Current popularity of plastic liningsappears to be well justified, because oftheir ease of installation, low cost andexcellent seepage control.

ACKNOWLEDGEMENTS

The authors wish to express theirappreciation to the numerous PFRApersonnel who provided information oncanal lining performance.

REFERENCES

1. First Progress Report on Experimental Canal and Dugout Lining.Soil Mechanics and Materials Division, PFRA. Saskatoon, Sask.March 1951.

2. Second Progress Report on Experimental Canal and DuguotLining. Soil Mechanics and Materials Division, PFRA. Saskatoon,Sask. April 1952.

3. Third Progress Report on Experimental Canal and Dugout Lining.Soil Mechanics and Materials Division, PFRA. Saskatoon, Sask.March 1957.

4. Five-Year-Report on ActivitiesUnder the Drainage Division.PFRA. 1949-1953.

5. Report of Drainage Investigations,Big Bend Extension, Taber Area.1950. S. H. Van Orman and E.Rapp. (Unpublished).

63