Full-Flowing Collection Conduits with Nonuniform Inflow

Abstract

Collection conduits flowing full with nonuniform inflow (variable rate of increase in flow with distance along the conduit length) include well screens (vertical and directionally drilled); submerged effluent collectors; and certain types of inboard weir configurations for settling tanks. Certain subsurface drains used in environmental engineering applications and civil engineering more generally may be inadvertently designed for full-flowing conditions. Formulation of the problem for such collection conduits is presented in terms of the applicable differential equation, slope invariance, the frictionless solution for a general cross section, a uniform-inflow solution, and the difference formulation. The importance of checking inflow uniformity is discussed and exemplified. Dimensional analysis is then employed to demonstrate the relationship between variables, leading to a new generalized numerical solution. That solution is presented in a graphical form which provides further useful display of the relationships between variables and quantitative information for design and analysis. The detrimental effects of flowing-full conditions in subsurface drains is demonstrated, and it is noted that existing design methods may unintentionally cause such conditions to occur.