Dr. Liu later applied linear systems theory to the simulation of contaminant transport in upper soils. Together with Dr. Keith Loague (now a professor at Stanford University), through WRRC he submitted a proposal to the US Geological Survey in 1987, entitled "Compatibility of Physically Based and Linear System Solute Transport Modeling Approaches and Their Conjunctive Application." This project and 34 others were selected for funding from among 275 proposals submitted in this open national competition. The University of Hawaii teamžs research benefited from valuable field data collected by, and comments from Drs. Richard Green, and Stephen Lau, as well as other researchers at UH.
The impulse response function of a linear systems model of chemical transport in soils takes the form of a gamma distribution function. The values of the two gamma distribution parameters for a given soil transport system can be evaluated by two regression equations, which correlate these parameters with basic soil properties. The linear systems model and the regression equations were tested by comparing calculated results with field measurements taken at Kunia, Hawaii (see figure below). Model testing of sodium bromide transport in soils at Kunia, Hawaii. Both net recharge rate and NaBr concentration are expressed in dimensionless forms.
The research team has developed a technology for integrating geographic information systems into the linear systems transport model. They demonstrated the utility of this technique as an environmental management tool by applying it in an environmental impact assessment of potential soil and groundwater contamination due to the use of synthetic chemicals in the industrial region of southern Taiwan.
Dr. Liu also applied the linear systems theory for river water quality modeling. Recently, he was invited by the American Society of Civil Engineers (ASCE) to contribute a chapter on "Linear Systems Approach to River Water Quality Analysis," which will be published in a forthcoming ASCE book entitled Environmental Fluid Mechanics - Theories and Application. A user manual and computer program documentation related to this chapter will soon be published as a Water Resources Research Center technical report.