Hydraulic calculation of dissipating outfalls

Summary

Recently, significant attention has been paid to the environmental issues in the reconstruction, upgrade, and construction of wastewater treatment facilities in the Russian Federation. In these instances, estimating the capacity (performance) of the final element in the treatment system, i. e. the discharge of effluents into a water body is obligatory. Calculating dissipating outfalls presents certain challenges, since this issue has received insufficient attention so far. Making hydraulic calculations of a dissipating outfall is proposed as not a calculation of one single element – the head – but of the entire system, i. e. supply and distribution pipelines, and all the existing heads (openings). Addressing this problem lies in solving a system of algebraic nonlinear equations describing flow distribution with variable withdrawal rates in the dissipating outfall under consideration. Consequently, the discharge rates through each head and the piezometric head values at all the outfall assemblies are determined. The proposed mathematical model of a dissipating outfall provides for not only estimating the functionality of an existing or planned outfall but also, in case of a damage (rupture) in the underwater part of the outfall, determining its parameters, i. e. the orifice area and the rate of the flow entering the watercourse through it. By analogy with pumps, the concept of a head and rate specification is introduced, providing for the use of one parameter (flow rate or head at the initial outfall assembly) to determine the other parameter eliminating the hydraulic calculation of the entire outfall. An example of a hydraulic calculation of a dissipating outfall with an estimation of the operating parameters is provided.

Key words

hydraulic design , pressure losses , distribution pipeline , headwall , variable abstraction , effluent discharge into a water body , dissipating outfall