Keywords: landfill caps, alternative covers, evapotranspiration covers, Oahu, Hawaii, water infiltration, tropics, water balance, vegetative covers, soil, run-off, vegetation growth
Alternative methods to control water infiltration for landfills: a case study in the tropics
Landfill caps made of synthetic materials are expensive. Compacted clay caps are also subject to desiccation cracks which negate the overall purpose of infiltration reduction. Vegetative cover caps, also called evapotranspiration covers, have been tested in arid climates. In this research, a vegetative cover using a naturally occurring soil of Hawaii was tested. As the annual rainfall at the site is more than the evapotranspiration demand, a portion of the run-off was routed offsite using run-off-enhancing structures such as rain gutters. The site contained six test plots on 4% slopes to simulate different components of water balance: two control plots, two plots with 20% surface area covered by the gutters and two more plots with 40% area covered by the gutters. The gutters were spaced uniformly and enhanced run-off in early stages of vegetation growth. With growth, the vegetation covered the gutters and the gutters did not receive as much rainwater. The difference in run-off between the 20% and 40% was not significant. If the gutters had been placed at a single location in the plots, they would not have been covered with vegetation, thus making them effective to produce runoff in most stages of vegetation growth.