construction and refurbishment of earthen irrigation channel banks

Microsoft Excel has quite a good present value function, called NPV. It alsoincludes optimisation and what-if analysis functions called Solver and Goal Seekrespectively, which can be used to find optimal solutions.13.4.5 Identify Asset LivesLife cycle cost analysis requires the realistic assessment of asset lives. The assetlife is the period in years from the time of construction or acquisition, to the timewhen the asset is expected to reach a state where it cannot provide acceptableservice because of physical deterioration, poor performance, functionalobsolescence or unacceptably high operating and maintenance costs.The lives of two identical assets operated under different conditions may not be thesame. Similarly assets consisting of different materials may have different lives,even though they are performing the same function. Because of the many factorswhich determine asset lives, the appropriate lives should be assessed in eachparticular case.A sound prediction of the remaining life of an existing channel is also important forlife cycle costing, and this requires a careful assessment of the rate and extent offuture deterioration of the channel.An earthen irrigation channel will have a wide variation in its life and rate ofdeterioration because of the varying influence of:• design• construction methods and quality• age of channel• soil types• usage history• environment• operating practices• maintenance regimes – past andcurrent• size of bank• velocity of flow and flow history• depth of flow• whether protected from animals• whether carp are in the channels• bank orientation to prevailing winds• fluctuations in water levels –magnitude and rate• extent and quality of refurbishmentThe evaluation of asset lives can be quite a complex process, and at best, only anestimate of an average life can be made for most long life assets, based on the ageafter which the asset falls below an acceptable limit or performance or at failure.What is unacceptable performance can depend on service perceptions andexpectations. Future influences can be different from those of the past.Predictions of asset lives can be based on:• performance modelling using condition monitoring and deterioration rates• historical records using survivor techniques• degradation models• time to failure models• accumulated experience• accelerated testingConstruction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 13-12