The firm will now draw up detailed plans for the 6.3km Trym Tunnel Relief Sewer, which will transfer flows directly from the north of the city to Bristol sewage treatment works.
The tunnel will start at Bristol Golf Club and pass deep beneath Catbrain, Henbury and Lawrence Weston.
Construction is expected to start in late 2019 for completion by 2023. The project is understood to be worth around £43m.
It forms part of Wessex Water’s north Bristol strategy to reduce flood risk, accommodate new development, improve overflow performance and future-proof the strategic sewers in north Bristol.