SEDIMENT SIZE AND GRADATION CONTROLS ON CHARACTERISTICS OF INERTIA INFLUENCED NON-DARCY FLOWS

Darcy’s law is known to be valid for flows with negligible or small inertia in aquifers. When the head gradient is large, or an aquifer consists of a more significant flow velocity, such as the case of pumping wells or surface water groundwater interactions near rivers, Darcy’s law deviates to non-Darcy relationship or the Forchheimer law, which takes on a form of a second order polynomial function with coefficients specific to sediment type. Non-Darcy flow can also be accounted for by a power-law form known as the Izbash equation, where the exponent is once again specific to sediment type. Despite numerous published experimental data, how these coefficients or exponents depend on sediment size and gradation is not well understood. In this study, we systematically sieved out clastic sediments into different grain sizes to conduct column experiments of pressure head-driven flow with head gradients of up to 10. The various sediment sizes are further combined in various proportions to obtain a variety of gradations determined by the Uniformity coefficient (C_u). We use Forchheimer and Izbash equations to determine how and if the coefficients and the exponents of the fitted equations are a function of the Uniformity coefficient. This information can potentially be applied to real-world hydrogeology in the field, giving insights on how the Darcy and non-Darcy flow or associated water-table gradient will react in aquifers and related surface water interactions in various watersheds.