Hydraulic assessment of non-circular-section building drainage

The development of non-circular cross-section in-building drains with a reduced invert cross-section will allow efficient low-flow performance by maintaining flow depth to aid solid transport. An enlarged upper cross-section will allow higher water and air flow rates to be handled. Such developments are essential if the water-conservation benefits of a reduced toilet flush volume are to be realized. The paper demonstrates the background to such solutions based on the ovoid or 'egg-shaped' cross-section sewers that have been used in Europe and the US for two centuries. The steady flow capacity of the ovoid shape is demonstrated, while the reduced wave attenuation in ovoid cross-sections is simulated, using the method of characteristics solution to the wave equations, and it is shown to be an indicator of improved overall solid transport efficiency. Solid transport results demonstrate the efficiency of non-circular sections and provide a direct comparison with the use of reduced-diameter circular drains already acceptable in conjunction with reduced water usage.