EFFECT OF GEOMETRY COMPUTATIONS AND NUMERICAL SCHEME ON THE RESISTANCE COEFFICIENT FOR UNSTEADY FLOW IN IRREGULAR CHANNELS

The problem of predicting flow resistance coefficient with sufficient accuracy. is
of great interest to hydraulic engineers. Realistic estimate of hydraulic resistance
is important to the proper design and analysis of irrigation and drainage
networks. Resistance (roughness) coefficient is a compound function of the
geometric properties of the channel, the fluid properties, and the varied flow
conditions prevalent in the open channel system. The purpose of this study is to
demonstrate the response of the applied method of irregular geometric properties
computation, the used numerical scheme, and the distance interval adopted in the
numerical model on the calibrated value of resistance coefficient.
The rectangular grid scheme of the method of characteristics is applied with
different methods of irregular geometric properties computation and different
value of distance interval. While, the Leap-Frog finite difference scheme is used
with only one method of geometric properties computation and one value of
distance interval. Measured field data of Tanta Navigation canal are used to feed
and calibrate the numerical models. Results of numerical experiments illustrate
that inaccurate channel geometry representation in the numerical models leads to
incorrect value for the calibrated value of roughness coefficient. Findings also
demonstrate that the applied numerical scheme as well as the schematization to
describe the channel geomeby by a series of discrete representation along the
reach being modeled has significant effect on the calibrated value of the
roughness coefficient.