How is the location of a tidal outfall determined?

It is based on comprehensive hydrographic surveys, dominant tidal current patterns, and the dilution required to meet statutory receiving water quality standards.

At what depth should the outfall typically discharge?

The discharge point should be located well below the Lowest Low Water Mark (LLWM) to ensure it remains completely submerged at all times for maximum dispersion.

What structural loads must be considered for submarine outfalls?

Designers must account for internal surge pressures, external hydrostatic pressure, wave forces, tidal currents, and seabed scouring.

IS 4111

: 2000

Code of practice for ancillary structures in the sewerage system, Part II: Flushing tanks

CurrentSpecializedCode of PracticeBIMEnvironmental · Public Health Engineering

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This code outlines the criteria for the planning, design, construction, and maintenance of tidal outfalls for discharging treated or partially treated sewage into marine environments. It covers essential hydrographic investigations, dilution modeling, hydraulic sizing, and structural stability against oceanographic forces.

Code of practice for ancillary structures in the sewerage system, Part II: Flushing tanks

Quick Reference Values

minimum self cleansing velocity0.6 to 0.8 m/s

discharge elevationBelow Lowest Low Water Mark (LLWM)

recommended initial dilution1:50 or greater (varies by environmental norms)

Practical Notes

Comprehensive bathymetric, oceanographic, and baseline water quality surveys are mandatory prior to fixing the outfall alignment.

Diffusers must be carefully designed to maximize initial mixing and prevent seawater intrusion (saline wedge) into the pipeline during low sewage flow.

Adequate scour protection, such as concrete weight coating or rock armoring, is critical to protect the outfall pipeline from wave action and ship anchors.