Numerical Study of the Seasonal Wave Action Developed at an Agricultural Water Reserve

Abstract

Extreme evaporation is a problem that has arisen across the majority of Australia over the past decade mainly due to minimal rainfall coupled with warmer than average temperatures. Up to this point in time, many different evaporation mitigating systems have been developed to provide water loss reductions for both the private and industrial sector. Ultrathin artificially synthesised chemical films (monolayers) are one such evaporation mitigation system, and have been employed extensively as they are relatively cost-effective, easy to deploy and are thought to have a minimal effect on water quality. It is well known that both wind and wave action can have a greatly negative influence upon the spreading ability, and in turn the overall performance of monolayers. Therefore, it is necessary to investigate the wind circulation patterns and associated wave motion for an example real-world agricultural water reserve that can be viewed as a typical deployment site for monolayers. In this investigation, a set of numerical models have been developed and evaluated for a closed dam in south-east Queensland, in order to better examine the hydrodynamic and wave conditions that directly influence the transportation of a monolayer across the water surface, and in turn control the evaporation reducing performance of a given monolayer. Specifically, this study has employed a two-dimensional hydrodynamic model and a spectral wave model by utilising the MIKE 21 program developed by DHI. Seasonal wind conditions were used as the major driving force in the wave development process, with the growth of wave height occurring parallel to the dominant wind direction. Both wave height and wave period were found to be dependent on the fetch length along with wind speed and duration. Waves were seen to develop along the direction of increasing fetch. In addition, the seasonal waves were calculated to not exceed a height of any greater than 0.11 m. From these outcomes, this numerical study has provided an accurate summation of wind generated wave conditions that can be used to predict the effectiveness, applicability and economic viability of a given monolayer if it were to be continuously deployed at the real-world water reserve.