Ecological Cover Systems for Waste Landfills
Conventional cover systems of waste landfills rely on barrier layers made of compacted clay,geosynthetics and geomembranes,either alone or in combination.Although barrier-type cover systems are sometimes described as impermeable,in practice it is intend to fail due to subsidence caused by waste decay,water and wind erosion,wet-dry cycles,freeze-thaw cycles,ultraviolet degradation and intrusion by burrowing animals.An ecological cover system consists of a uncompacted soil layer covered by native plants,which acts not as a barrier,but as a reservoir that stores moisture during precipitation events,and then releases it back to the atmosphere as evapotranspiration.Ecological cover systems are more inexpensive,easily constructed and maintained than conventional cover systems.To search reasonable design of ecological cover systems,percolation control experiments of different cover systems were implemented in Comprehensive Experimental Station of Water Environment of Wuhan University,unsaturated flow analyses and water balance calculations of different ecological cover systems were conducted,the results showed that the soils suitable for ecological covers are loam and clayey loam with soil bulk densities between 1.1 and 1.5 g/cm3,required soil thickness for Wuhan region should be 120～140 cm,the reasonable vegetation type is an mixture of deep-rooted grasses and shrubs.