Subcritical open-channel junction flow

This study presents an analytical approach for solving both the upstream-to-downstream depth ratio, (Y) over bar and the energy loss through junctions of equal-width subcritical flows over horizontal beds, based on three experimental test setups with junction angles, theta being 30 degrees, 45 degrees, and 60 degrees. Under a known discharge ratio, el between upstream and downstream of main channel and a known downstream boundary condition, (Y) over bar is computed using a third-degree polynomial function. (Y) over bar is found to increase with increasing theta and with increasing F-rd. The energy loss coefficient, K-e, through the junction is expressed as a function of (Q) over bar, downstream Froude number, F-rd, and (Y) over bar. For F-rd < (4 (Y) over bar(6) + 2)(1/2) - 2 (Y) over bar(3), it is found that K-e increases with increasing theta and F-rd.The results of the analytical approach are found to be in fairly good agreement with the experimental values and the values obtained by other studies. The polynomial function is further transformed to an approximation equation allowing (Y) over bar((Q)over bar> - Delta (Q) over bar) to be computed by (Y) over bar((Q) over bar). Finally, an equation relating the increment of the water depth and the discharge at the upstream and downstream of junction is proposed to serve as an interior boundary condition for one-dimensional numerical simulation.