construction and refurbishment of earthen irrigation channel banks

channels are operating and so avoids works being restricted to the short nonoperationalperiods where there is often poor site conditions due to wet weather.With outside bank re-construction, the established silt seal is not disturbed.Whereas with total bank reconstruction, the silt seal is removed and this mayincrease seepage for a period of time in lighter soils.There are disadvantages to this method as against total re-construction of channelbanks:• The technique further widens the waterway width than its original design;therefore velocities are slow, and increased siltation and weed growth may occur.• Increased evaporation and seepage as there is a greater water surface and wettedperimeter• Increased volume of water required to fill channels• Land acquisition may be required to accommodate a wider channel profile• Material Selection Refer Section 15• Compaction Refer Section 16• Construction Refer Section 19• Waterway excavation, if required Refer Section 20.4.1.5• Re-batter inside batters Refer Section 20.4.1.5A typical re-construction approach would consist of:1. Dozer strips the outside portion of bank down to solid base, a minimum of200mm below natural surface level, leaving approximately a 0.5 metre minimumbank width at the water level to contain water during construction. The waterface of the bank is left untouched at this stage.2. Dozer scarifies the surface of the bench.3. Trucks deliver material onto the bench from the borrow pit.4. Dozer spreads and compacts material on the bench in layers to requiredcompaction density.5. When the compacted bank design height has been reached, protective cover isplaced over the crest (if no access) and outside batters.6. The waterway is enlarged, if required.7. The inside batters are re-shaped to establish a stable profile.8. If required a layer of protective granular material is placed on the water face ofthe bank.9. Access track is constructed.10. Longitudinal fencing if protection is required.Refer to Section 19 on Channel Bank Construction.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 20-9