Norbury Brook

From the Wikipedia page

A tributary of the River Wandle, Norbury Brook rises near Lower Addiscombe Road and flows north-west through Selhurst, Thornton Heath and Norbury to join the Wandle at south Wimbledon.

A short stretch of this is visible in South Norwood at Heavers' Meadow, near Selhurst Station, where the brook can be seen in a concrete channel next to the British Rail works as it runs north west along the bottom of the site before disappearing beneath Selhurst Road. It is fenced off here because it can be very dangerous, especially after a rain storm, where the water level can rise several feet in a few minutes as the water rapidly drains from the roads and hard surfaces around and into the surface water drain.

The brook reappears in Thornton Heath Recreation Ground, running along the western boundary of the park in a deep concrete channel. Most of the time the brook is fairly shallow, but during heavy rainfall water quickly drains from the adjacent built up areas and the water level rapidly rises. It then continues behind several private houses in between before reaching Norbury Park where, once again, it is hidden behind a tall fence.

The brook continues west, to form the boundary between Norbury and Streatham on London Road at Hermitage Bridge, where it is one of the few rivers remaining overground in the area. West of the bridge the brook becomes the River Graveney, where it flows on to join the Wandle, and ultimately the River Thames.