Kai Tak River: riverbed inspection, drain seals and diversion screens

The Kai Tak River runs straight through one of the busiest construction sites in Kowloon. Building the Central Kowloon Route's Kai Tak East section meant working in and over a live river, and a lot of that work had to happen underwater.

2020: mapping the riverbed

Before the temporary works went in, divers swam the riverbed with a CCTV camera and recorded what was down there, chainage by chainage: loose rubble of 300–600 mm, slabs of broken concrete, old steel frames, channel sections and the depth of silt. Everything was plotted onto one riverbed plan so the contractor knew exactly what had to be cleared.

In the same year we designed the steelwork to seal off a branch drain where it joined the box culvert.

2021: sealing live drains

Several drain pipes still discharged into the river where the new structures would sit. We designed bolted seal plates for the Ø1,200 mm and Ø1,350 mm pipes: a 6 mm steel sheet stiffened with 100 × 50 mm channels, fixed to a 50 × 50 mm angle ring with twelve M16 bolts, a 10 mm rubber pad and a stop-leak compound behind it, and sandbags packed against it. Each piece is sized for a diver to carry and fit by hand.

2022: diversion screens around the bridge platform

To steer the river flow around the piles of the new bridge platform, we installed heavy tarpaulin screens from +2.5 mPD down to −1.5 mPD at 8–10 locations. The sheets came in three sizes (6.5 × 4 m, 6 × 4 m and 1 × 4 m), each held by three Ø48 mm galvanised pipes at +2.5, +1.5 and −1.5 mPD and tied back to the platform frame.

1. Sheets and pipes are prepared on a working platform on the bank.
2. A crane lifts them onto a small boat, which carries them along the river to each location.
3. Technicians stage them at +3.0 mPD; divers fit them below the waterline.
4. Every location is photographed above and below water and handed over in a report.

Stage 2 ran from April to May 2022 and Stage 3 in September 2022.