 Thus, along much of the Brent's present-day course, one can make out the water-meadows of rich alluvium, which is augmented by frequent floods.After the river took its present-day course, many of the banks of the Thames Estuary and the Thames Valley in London were partly covered in marshland, as was the adjoining Lower Lea Valley.Streams and rivers like the River Lea, Tyburn Brook and Bollo Brook drained into the river, while some islands, e.g.