Integral Jet Model for Flow from an Open Channel into a Shallow Lake or Reservoir

Abstract

Jet-like flows in sudden channel expansions with horizontal or sloping bottoms are investigated. These flows occur at inflows to lakes and reservoirs or at wastewater discharge sites. An integral analysis approach has been used. The main objective of the study has been to develop a method by which the dilution of inflows to lakes or reservoirs can be predicted if t.he geometry (simplified) and inflow conditions are known. If the. diffuser angle, the sloping angle of the bottom inflow channel aspect ratio and inflow densimetric Froude number are given, the equations which will be presented can be used to estimate the dilution of plunging or non-plunging inflows. This information is needed in one-dimensional water quality models of stratified lakes or reservoirs. The integral jet flow analysis used herein includes a similarity hypothesis for velocity profiles, application of the entrainment principle and consideration of bottom friction effects on momentum. A general theoretical model is developed to predict jet centerline velocity, width and dilution of non-buoyant turbulent jet flows over horizontal or sloping bottoms in abruptly expanding channels. Wall effects in gradually expanding channels are also investigated for half jets. Predictions obtained with the theoretical model are compared with some experimental data of jet dimensions and dilution. The model is applied to geometrically simplified field conditions to illustrate effects of inflow channel aspect ratio, friction and bottom slope. All of these effects are found to be significant. As a side product a Gauss fitting method has been developed to analyze a finite number of laboratory measurements in horizontal diffuser flows with finite water depth. In an Appendix purely empirical equations for the dilution of horizontal jet-like flows through diffusers are also developed. Experimental results of density induced plunging flows into reservoirs (negatively buoyant) and of non-buoyant jet flows have been used.