construction and refurbishment of earthen irrigation channel banks

Earthen linings and buried geomembrane linings do not permit velocities higher thanin unlined channels and the dimensions can not be reduced. Their economicjustification depends on the value of the water saved by reducing seepage and onbenefits from preventing waterlogging and salinisation.22.4.4 Reduced Operation and Maintenance CostsWhere channels are supplied by pumping plants and seepage loses can be reduced bylining, savings in pump size and operating costs can be achieved.The type of channel lining being considered will influence the savings inmaintenance costs. For hard surface linings such as concrete, the benefits caninclude reduced weed problems, less damage from animals, reduced silt removal andprotection from scour and erosion.A large item of recurring maintenance on many channel systems is weed control, andhard surface linings such as concrete, which are relatively impenetrable by weeds,can greatly reduce the cost of weed control in the channel waterway. Seepage fromunlined channels can also stimulate the growth of land-type weeds outside thechannel banks, and lining can deter this.The greater velocities permissible in channels with hard surface linings can alsoreduce maintenance costs when silting and erosion are significant problems. Hardsurface linings are resistant to erosion, and if the slope of the channel is sufficient touse high velocities, the need for routine silt removal can be reduced. The silt, byremaining in suspension at the higher velocities, does not settle as much in thechannel, but rather more of the silt is deposited on the land being irrigated.In areas where burrowing animals and yabbies are prevalent, channel leaks occur as aresult of holes burrowed through the banks. The cost of repairing the banks, the lossof water and the property damage caused by the escaping water can be considerable,and hard surface linings being practically impenetrable to burrowing animals willlargely deter such actions.These benefits would generally not be applicable to channels with earthen or buriedmembrane linings. Buried membrane linings or compacted earth linings do notprevent weed growth in the channel. Maintenance costs related to aquatic and bankweed control, therefore, are not reduced by these types of lining. However, if theburied membrane linings or compacted earthen linings had a substantial crushed rockor gravel cover this would substantially reduce erosion, discourage burrowinganimals and provide less favourable conditions for weed growth compared to anunlined channel.An adequate maintenance regime for concrete lined channels can be relatively costly,if the integrity of the lining is to be preserved, especially towards the end of its life.Cracking must be identified and repaired promptly, and weeds controlled on the crestof the channel bank, where they encroach in the waterway, and roots widen andconceal cracks. Water leaking from cracks for an extended period can erode thesubgrade and cause the failure of an entire section of lined channel.Refer to Section 13, Life Cycle Cost Analysis.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 22-12