Applicability of a Numerical Simulation Model for a System Coupling Atmospheric Gas, Surface Water and Porous Medium to Banks with Complex Configuration

Abstract

The aim of this study is to investigate applicability of a numerical simulation method (ASG method) for coupling porous media system (saturation formulas) with an atmosphere (gas) － surface water two phase-flow system to practical problems for overtopping that surface water overflows a bank. In this study we conducted numerical simulations for overtopping a trapezoid bank with permeable surfaces, for overtopping trapezoid bank with a berm and permeable surfaces and for overtopping a trapezoid bank with a berm and impermeable surfaces. Moreover it was assumed that these banks were made of sand (the intrinsic permeability 1.737×10^-11 m²) and the impermeable surface had the intrinsic permeability 1.0×10^-18 m² and the thickness of 0.2 m. Consequently, it was found from the results of the numerical simulation with ASG method that there was a zone unsaturated with water (unsaturation zone) in the trapezoid bank with the permeable surfaces and two unsaturation zones in the bank with the berm at the elapsed time 9,000 sec after overtopping. Then the gas pressure in the unsaturation zone rose up to 12 kPa in these cases. Finally in these cases the gas in the unsaturation zone went out the bank. On the other hand the unsturation zone finally remained in two areas beneath the impermeable surfaces of the bank covered with the impermeable material as the results of ASG method. Then the gas pressure also rose up to 8 or 12 kPa in the unsaturation zone. Therefore it was recognized to be able to reproduce the overtopping the banks with various configurations, water contention curves and surfaces and that the gas in the unsaturated zone rose up to 8 － 12 kPa, by using ASG method. It is particularly significant that ASG method can represent an interaction between the gas and water in the porous medium and those in surface water considering balance of pressure.