Derived Models for the Prediction of Cole’s and Dip Parameters for Velocity Gradients Determination in Open Natural Channels

Abstract

Measurement of vertical velocity in open channel hydraulics is a very reasonable exercise that attracts peculiar results in stream flow. Observations were made on set of values obtained from calibration of models on continuous longitudinal stream flow. They showed that, there emanated effects of eddy currents. The exercise is characterized by downward trend in the velocity gradient resulting in a dip. However, at the early stage of flow development, a stage corresponding to the bed region, where little or no flow occurs, there had been what should be referred to as hypothetic zero flow region. There is vertical relationship between flow pattern developing and the position from the bed and free surface. Local scouring is induced around structural elements such as a bridge pier, an abutment at the lower region eddies and adjourning loose embankment areas. Occurrence is as a result of interaction between turbulent flow and sediment particles at the bed. The entrainment of sediment particles from the bed is probabilistic and definitely dependent upon flow characteristics and strongly influenced by instantaneous shear stresses developed along stream movement. The computed values of Cole's and Dip parameters for vertical velocities estimation were 0.77 and 0.78 respectively. For accurate measurement of vertical velocity profiles, a constant (א) has been introduced in models for velocity gradient determinationא) .) This coefficient has the estimated value of 3.6 - using mathematical iteration methods advanced by Jacobi and Hardy Cross. The proposed models (PIDMWLEL and PIDMWLL) are recommended to be most suitable for predicting velocity profile in open channels, when aspect ratios are greater than five (5) and ten (10).

Keywords: Appearance; calibration; channel; flow velocity