construction and refurbishment of earthen irrigation channel banks

Where a channel has relatively high seepage, the development of a groundwatermound beneath the channel is likely. When this mound approaches the landsurface, a discharge area adjacent to the channel may develop. Refer Figure 21-2.Groundwater discharge restricts the growth of non-salt tolerant species which leadsto productivity losses. Continual discharge eventually inhibits the growth of salttolerant plants as well, exposing the soil to erosion.Groundwaterdischarge zoneGroundwaterdischarge zoneEvapotranspirationGroundwater MoundEvapotranspirationFigure 21-2Local effects of Channel SeepageAccessions from on-farm structures, such as channels and storages, and agriculturalactivities also contribute significantly to local groundwater levels.21.4.4 Regional ConsequencesChannel seepage can contribute to the general problems of rising groundwaterlevels and the formation of perched watertables with consequent loss ofproductivity of lower lands, as follows:• loss of productive land• land value degradation• increases in watertable levels• increases in salinisation of soil and water• loss of vegetation• loss of bio-diversity• increased farm operating costs• increases in infrastructure maintenance and replacement costsSeepage losses from irrigation channels can add pressure to regional aquiferspotentially raising groundwater levels across a broad area. Rising groundwaterlevels result in waterlogging and likely salinisation of surface soils. Risinggroundwater tables and subsequent land salinisation has been observed in manyirrigation areas in Australia. Crop yield is significantly influenced by shallow,saline groundwater table lying within a critical depth (less than 2m) below the landsurface.Construction and Refurbishment of Earthen Channel Banks August 2002 – Edition 1.0 21-11