construction and refurbishment of earthen irrigation channel banks

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Seepage is a complex hydrologic phenomenon. Because of the many variables involved,no single method for computing the rate of seepage has been developed. When water isflowing in a channel it immediately starts to move into the air spaces between theparticles making up the wetted perimeter of the channel. This movement is acombination of capillary flow and percolation. The capillary flow is caused by thecapillary attraction of the fine passages between the particles of the bed material, whereaspercolation is caused by the action of gravity enforcing the water through the pores of thebed material. The action of gravity is always downward, but capillary attraction operatesin all directions and may cause the water to rise above the level of the water in thechannel. Capillary movement is extremely slow and is normally small in comparisonwith percolation.Refer to Section 22.4.1, Waterlosses and Section 22.5.10 Acceptable Seepage Rate.21.3 Factors Affecting SeepageSeepage processes can be quite complex and the interpretation of seepage test resultsfrom a channel require a knowledge of the factors affecting it.The rate of seepage and the slope of the seepage gradient leading from earthen channelsare related to:• Characteristics of the material at the soil-water interface and below the channel bed- permeability of the bed and banks of the channel- permeability of the underlying soil layers- percentage of entrapped air in the soil- action of capillarity and gravity- chemistry of the soil- soil temperature• Channel geometry- depth of water in channel- channel shape and wetted perimeter of the bed and banks• Characteristics of channel water- chemistry of water- salinity of water- amount of sediment carried and deposition of silt- length of time that water has been in the channel- water temperature• Flow characteristics- velocity of flow- total time of channel operation• Position of the watertable and hydraulic gradient- location of watertable relative to the channel- irrigation of adjacent land- evaporation from watertable via capillary rise- groundwater pumping in vicinity of channel- surface and sub-surface drainage in vicinity of channel• Ground slope at right angles to direction of channel flow• Microbiological activity• Barometric pressure and weather conditions• Surrounding vegetation of the channelConstruction and Refurbishment of Earthen Channel Banks August 2002 – Edition 1.0 21-4
Since many of these factors are closely related, act simultaneously and some of them tendto counteract each other, so it is difficult or practically impossible to determine therelative contributions of each to seepage. Therefore, the factors thought to be leastimportant to seepage losses, such as soil temperature, velocity of flow and ground slopeat right angles to the flow, generally are not taken into account.The main factors known to have a definite effect on seepage rate can be grouped asfollows:1. Characteristics of the channel surface and subsoil.2. Depth of water in the channel, wetter perimeter of the channel and the depth togroundwater.3. Amount of sediments in the water, velocity in the channel and length of time thechannel has been in operation.Group 1Permeability is the soil property that indicates the relative ease with which water willflow through the soil. Permeability is the ability of a soil to conduct or dischargewater under a hydraulic gradient. This property is mainly dependent on the porosity ofthe soil, shape and arrangement of the soil particles, soil density and degree ofsaturation.Coarse-grained soils are highly pervious and have high permeability co-efficients;fine-grained soils are much less pervious and have low co-efficients.The co-efficient of permeability K, cm per sec, is defined by Darcy’s law:Q = KiAWhere; Q = rate of flow of water through soil mass, cm 3 per seci = hydraulic gradient or total head lost per unit of flow distance, cm per cmA = total cross-sectional area of soil through which flow takes place, cm 2A survey of the soil profile along a proposed channel alignment is the most importantsingle step in a pre-construction seepage investigation. This survey should determinethe location, extent and physical characteristics of the various underlying soil layers.The sequence of permeable and impermeable strata and the capability of these strata totransmit water will largely determine the amount of water lost by seepage.Group 2The following relationships have been found to exist between seepage and water depthin the channel, depth to groundwater and wetter perimeter of channel:1. Seepage losses generally increase with increase of water depth in the channel,although the two factors are not directly proportional. Depth of water has beenfound to have more influence on seepage rate when the rate is high than when therate is low.Construction and Refurbishment of Earthen Channel Banks August 2002 – Edition 1.0 21-5
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Your comments on the format and con
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During the course of this project,
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AcknowledgmentsThese Guidelines rep
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FundingFunding of this project was
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Table of ContentsBook 1SubjectPage
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1. Introduction1.1 GeneralGood asse
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(iv) provide proven practice approa
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3. Research Procedure3.1 Terms of R
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4. How to use these Guidelines4.1 W
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6. Units of MeasurementQuantity Uni
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8. Earthen Irrigation Channels8.1 D
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8.3 ReferencesAustralian National C
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9.1 IntroductionA key input to adva
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Data from Goulburn-Murray Water’s
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General 1 2 3 4 5 6DescriptionRisk
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Channel BankSequential Deterioratio
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9.2 ReferencesGutteridge Haskins &
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10.2.3.1 Dispersive layer of materi
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Causes ofSpecific factorDeteriorati
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10.1.2.5 BendsA bend in the channel
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10.1.4.1 Construction techniqueIrri
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10.1.5.4 Overtopping of banksIn ade
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In the past maintenance techniques
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Maintenance is a continuing require
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10.1.7.4 Yabbies/fresh water crayfi
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Direct removal ofmaterial by entrai
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Figure 10.10 shows longitudinal cra
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10.2.3.3 Irregular compaction - bri
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10.3 ReferencesEmerson W (1996), pe
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11.1 GeneralThe Investigation and P
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iv) Available fill materials and, w
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12.15 Radius of Bends .............
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There are several ways a channel ca
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• Land acquisition extent and typ
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The investigation should generally
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• Backfill: 10% compaction factor
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1. Flow Area, A, is the cross-secti
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after ageing and weed growth. If an
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elationships may be the controlling
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These maximum velocities should be
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Thus channels are usually designed
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Some of the design issues that shou
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12.12.1.3 Best PracticeEither of th
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12.13.2 Channel MaintenanceIncrease
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along a channel. The depth of the w
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12.13.4.7 Change of AlignmentThe in
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12.15 Radius of Bends12.15.1 Flow A
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12.16 Channel Cross SectionThe cros
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Some irrigation authorities use one
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12.16.2 BanksChannel cross sections
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Unless the bank is very high, the s
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The stability of channel batters ca
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drop bars become difficult and time
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Both the height above the bed and t
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• enable maintenance of the chann
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- Access agreementsA description of
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13/08/02 19:2012.20 Channel Tenure
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13/08/02 19:20As with the damage to
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13/08/02 19:20Advantages of Protect
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- gates provide a better deterrent
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13/08/02 19:20When considering expo
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13/08/02 19:20A typical design draw
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13/08/02 19:20Sinclair Knight Merz
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13.1 IntroductionIn many irrigation
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For example, the initial constructi
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13.2.6 When to use Life Cycle Analy
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The timing of the life-cycle costin
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• assess cost of collecting missi
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Microsoft Excel has quite a good pr
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The costs used in these methods sho
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Life CyclePhaseInvestigationDesignC
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Life CyclePhaseMaintenanceRehabilit
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ReplacementProject managementInvest
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Residual valueLegal feesInsuranceAd
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13.4.6.2 Recurring CostsChannel con
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$1.00.80Percent ofValue of$1.00.60.
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13.4.11 Evaluate ResultsThe results
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13.6 Tipsthe way open to incur sign
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14. Risk AnalysisTable of ContentsS
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Consequences for irrigation authori
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15. Material Selection and TestingT
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c) Shrinkage - will the bank crack
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depth. For this reason, the soils o
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Natural moisture content should als
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The study identified some confusion
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15.4.2 Determination of the plastic
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1. Preparation of PatTake approxima
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EmersonClass No.Degree ofDispersion
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15.7.1 Coarse grained soilsIn this
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sufficient gravel for erosion resis
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GroupSymbolsSuitability for Earthen
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The uniform application and thoroug
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essential that the chemical is thor
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Where laboratory testing facilities
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Clays are the plastic fines. They c
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etween the soil sample and the wate
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16. Compaction ControlTable of Cont
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16.1 PurposeDuring this research pr
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All compaction equipment utilises s
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The soil density required for a cha
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In the past, a method specification
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Low permeability and high stability
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16.10.1.1 Tamping Foot RollerTampin
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16.10.1.5 Non-Circular Impact Rolle
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16.10.3 Compactor OperationsAfter t
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16.11.4 Moisture Content ControlBef
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16.12 Density Control Tests and Pro
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Correlation with local materials an
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The main advantages of the Nuclear
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Figure 16.4Hilf Density Ratio Repor
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The location and test results for e
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16.14.3 Reporting and RecordsTest r
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16.16 Tests for small projectsThe s
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The advantages of the Drop Test are
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AS1289.6.3.2-1997AS1289.6.3.3-1997A
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17. Protective CoverTable of Conten
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The bank dries and cracks from the
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17.5 Specifications17.5.1 GravelPar
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17.6 Establish Vegetation CoverTops
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Species Growing Conditions Establis
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17.7.2 Rope Wick ApplicationMuch of
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There are a number of fibre mats or
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17.10 Australian StandardsAS1289.3.
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18.1 IntroductionFor many earthen c
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When re-shaping the batters of exis
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LifeCrestOld bank lineBattered bank
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Photos\inside batter\CG7channel2arm
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4. To help place the rock material
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False ToeFigure 18.8Protective laye
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The confinement system would be adv
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• Able to survive during non-oper
Page 266 and 267: 18.6 ReferencesHutchison D & Locke
Page 268 and 269: 19.20 Guidelines on Field Quality C
Page 270 and 271: Construction and Refurbishment of E
Page 272 and 273: • Figure 19.2)3. Temporary Bench
Page 274 and 275: The capabilities and limitations of
Page 276 and 277: 19.3.1 Construction EquipmentThe ba
Page 278 and 279: construction. The aim of scarifying
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Page 282 and 283: The thickness of each layer will va
Page 284 and 285: distribution. The use of alternativ
Page 286 and 287: 19.8 Construction RecordsAdequate r
Page 288 and 289: 19.12 Protective Cover on Crest and
Page 290 and 291: 19.21 Australian StandardsAS 1726-1
Page 292 and 293: 20.1 ScopeAustralia’s earthen irr
Page 294 and 295: Bank re-construction normally requi
Page 296 and 297: •meter outlet locations and type
Page 298 and 299: In the case of channel bank refurbi
Page 300 and 301: 20.4.1.1 StrippingWith outside bank
Page 302 and 303: All public roads to be used by truc
Page 304 and 305: 5. Material is delivered by trucks
Page 306 and 307: Need to drain and de-waterEBM befor
Page 308 and 309: significantly and a more conservati
Page 310 and 311: Aim for crest width ofabout 2 metre
Page 312 and 313: Refer to Section 18, Inside Batter
Page 314 and 315: 21.8.10 Re-alignment ..............
Page 318 and 319: 2. Seepage losses increase as the d
Page 320 and 321: Refer also to the following section
Page 322 and 323: 21.4 Channel Seepage ConsequencesSe
Page 324 and 325: Channel seepage is one of the sever
Page 326 and 327: Seepage is proportional to soil per
Page 328 and 329: Methods based on vertical flow meas
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Page 332 and 333: Flow NetsA flow net is a system of
Page 334 and 335: Data from indirect measurement proc
Page 336 and 337: (ii) EM SurveyElectro-magnetic (EM)
Page 338 and 339: The volume of waterloss from the dr
Page 340 and 341: 21.7.3.2 Inflow-Outflow Method (Dyn
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Page 346 and 347: Stable IsotopesThe basis of testing
Page 348 and 349: To be most successful, there needs
Page 350 and 351: 21.8.6 Surface interception drainag
Page 352 and 353: KeyWatertable before tree plantingW
Page 354 and 355: • The preparation of a best pract
Page 356 and 357: 21.11 ReferencesAustralian National
Page 358 and 359: 22. Channel LiningTable of Contents
Page 360 and 361: 22.1 IntroductionThe conservation o
Page 362 and 363: The different types of channel lini
Page 364 and 365: Table 22-1Unlined Earthen Channels
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Lining of channels will not elimina
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To supply a given discharge, the cr
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22.4.5 Structural SafetyThe stabili
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soil pressures and under-drainage i
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Concrete linings are suitable for b
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22.5.12 Availability of Constructio
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esistance to erosion. To improve th
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Construction and Refurbishment of E
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22.7.1.2 General Design Considerati
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22.7.1.4 Lining ThicknessThe thickn
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particular problems, but in smaller
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Where the earth lining finishes abo
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control where the channel material
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sand requires about 5% cement by we
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22.7.6 Soil SealantsSoil sealants a
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22.7.7 Cost of Earth LiningsThe cap
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Although they can assist with shear
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22.8.2 Membrane Liner TypesGeomembr
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Polyethylene has also appeared in m
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FPP resistance to common chemical e
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The base coat and seal coat rates m
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A common and misleading argument is
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These thermal expansion and contrac
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Another factor is the ability to ha
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Some lining methods expand and cont
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22.8.9.1 Geomembrane ThicknessThe t
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Cover typeThickness ofEarth fill(m)
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22.8.9.5 Cover MaterialGeomembranes
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As well, velocities which are permi
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22.8.11 FencingWhen livestock, part
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22.10 ReferencesAlther GR (1987), T
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23. Measures to Reduce the Rate ofD
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Channel DesignBank MaterialDeterior
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Stock and VerminAdjacentlandholders
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To ensure that a channel bank has a
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Advantages of Draining• Allows fo
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To efficiently maintain a channel,
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Compared with other countries where
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23.4.7 LeaksTransverse cracks are t
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23.5 Reduction of Deterioration due
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Photo 23-1Channel bed showing mumbl
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Thus, control of carp by draining c
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The disadvantages of a biological c
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Carp have been blamed for erosion o
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Management Groups gives guidelines
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Organisation Contact Details Aims/A
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Chemical treatment is often recomme
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23.7 Reduction of Deterioration due
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Grey Parrot Pea - Dillaynia cineres
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Lodge G (1998), Review on Fish Barr
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cation exchange capacity (CEC) a me
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fetch the distance over which the w
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plant term used for construction eq
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supply level the supply level is a
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