To estimate the outflow over a rectangular sharp-crested side weir, the discharge coefficient in the weir equation needs to be known. Although this type of structure has been designed and used extensively by hydraulic engineers, a universally acceptable discharge coefficient does not exist. In this study over 250 laboratory tests were conducted, and the results were analyzed to find the influence of the flow hydraulics and the geometric, channel, and weir shapes on the coefficient. The results show that for subcritical flow the De-Marchi assumption of constant energy is acceptable, and the weir discharge can therefore be used. Furthermore, it was discovered that the De-Marchi coefficient of discharge is a function of the upstream Froude number and the ratios of weir height to upstream depth and weir length to channel width, whereas the channel slope in subcritical flow can be ignored. Hence, an accurate equation for the coefficient of discharge is introduced.

Discharge coefficient for sharp-crested side weir in subcritical flow

The discharge coefficient of a lateral opening in a prismatic trapezoidal main channel is determined for subcritical flow conditions from considerations of the conservation of energy and the conservation of momentum. The latter requires an empirical relationship for the local downstream component of the spillage velocity with the local downstream velocity in the main part of the channel. The discharge coefficients obtained by both considerations for a broad range of Froude numbers, combination of both side slopes of 1V: mH with m=0, 0.5, 1.0, and 2.0, and different lengths of lateral opening are found to be nearly the same. The measured water depth just downstream of the lateral opening is not recommended for use in the numerical determination of the discharge coefficient and the reasons are discussed in detail. The discharge coefficient is found to be related to the upstream Froude number and this relationship is empirically established.

Discharge Coefficient of Lateral Diversion from Trapezoidal Channel

Side weirs, also known as lateral weirs, are flow diversion devices widely used in irrigation as a head regulator of distributaries and escapes, land drainage, and urban sewage systems. The studies on the subject have been generally focused on rectangular and triangular side weirs located on a straight channel. However, the same is not true for labyrinth side weirs. The current studies deal with sediment transport and scour problems around side weirs and lateral structures. The investigation of the hydraulic effects of labyrinth side weirs to increase discharge capacity of them has been studied in this particular work. In the study, 2,830 laboratory tests were conducted for determining discharge coefficient of labyrinth side weirs, and results were analyzed to find the influence of the dimensionless weir length L/b , the dimensionless effective length L/l , the dimensionless weir height p/ h1 , triangular labyrinth side weir included angle θ , and upstream Froude number F1 on the discharge coefficient, wa...

Discharge Capacity of Labyrinth Side Weir Located on a Straight Channel

Application of two different neural network techniques to lateral outflow over rectangular side weirs located on a straight channel

Determination of capacity of labyrinth side weir by CFD

Observations at numerous cross sections in a side weir channel showed that the total energy of flow decreases substantially along the channel, contrary to the assumption that has frequently been made. The decrease in total energy occurs because the longitudinal component of velocity of the spill flow is greater than the longitudinal velocity of the flow remaining in the channel. A satisfactory flow equation is derived from momentum principles and this is further developed into a computer technique for calculating flow profiles and spill discharges for side weirs.

Ahmed El-Khashab

Papers

Experimental Investigation of Flow Over Side Weirs

Closure of "Experimental Investigation of Flow Over Side Weirs"