construction and refurbishment of earthen irrigation channel banks

23.2 Reduction of Deterioration – Construction PhaseActions to be taken to reduce deterioration at the Construction phase of a project can befound in Section 19, Channel Bank Construction. AlsoSection 15, Material Selection and TestingSection 16, Compaction ControlSection 17, Protective CoverSection 18, Inside Batter Treatment23.3 Reduction of Deterioration – Operation Phase23.3.1 Rate of Channel Filling and Draining23.3.1.1 PrimingA great deal of care is needed when running water for the first time in newearthen channels, as the banks and backfill around structures may not besufficiently compacted and settled. Priming, the progressive filling of a newchannel over several weeks, will enable the banks to absorb moisture and settle;thereby avoiding many problems and any weaknesses that do develop can bedetected and repaired before breaks occur. If conditions permit, priming of newchannels should be started 2 to 3 weeks before water is needed. This allows timein case the need to repair the channel develops during the priming.23.3.1.2 FillingThe filling of earthen channels at the start of operational periods should not bedone rapidly. In old channels, water should be turned in from 1 to 2 weeksbefore delivery will be required at full-flow depth. In more dispersive soils, rapidfilling of the channel can lead to the fast saturation of the bank material, causingthe clay particles to disperse which speeds up the bank deterioration processesand can lead to piping failure and leakage.23.3.1.3 DrainingDraining water out of a channel too quickly may be more harmful than filling tooquickly. The rapid draining of channels can lead to the slumping of the saturatedbank material into the channel and the speeding up of bank deteriorationprocesses considerably, with the steeper the batter slope, the greater the impact.The acceptable draining rates will depend on the individual bank material, batterslopes and bank height. A maximum rate of change in water level should beestablished for each channel system in order to minimise damage from rapidwater level fluctuations. As a rule of thumb, experience has shown that the rateshould be limited to about 150 mm in 24 hours for a typical trapezoidal channelsection in average clay loam soils.23.3.2 Operating at Design LevelConstruction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 23-6