The Crane Valley Partnership

Risk of Flooding

The catchment has lost much of its floodplain to housing development in the 1800s. As a result, flood events became a regular occurrence by the turn of the 20th Century.

Surface water runoff and river levels

The impermeable London clay geology throughout the catchment makes runoff relatively rapid during periods of rainfall. The predominant urbanisation of the catchment has exacerbated this natural situation. Concreted streets drain directly into surface water sewers that discharge into the river when it rains. In the catchment’s natural state, water was able to drain through soil, ensuring a slower release into the river and surrounding floodplain. In its urbanised state, water is quickly flushed into the watercourse causing river levels to sharply rise, sometimes overtopping the river’s bank.

Loss of Natural Floodplain

The urbanisation of the catchment has also seen housing and industrial developments encroach on the floodplain. This has led to the river being put into restrictive structures and channels to prevent it from flooding these areas. Although this can prevent flooding in a localised area it can be responsible for moving the problem downstream to areas where there is a smaller area for the river to flood.

Restrictive Structures

Many reaches of the river, especially small tributaries and historical drainage ditches, have been either culverted, canalised, turned into sewers or are significantly engineered. It is believed that some flooding in the northern part of the catchment is caused by the overflowing culverted tributaries, manholes and drainage systems.

Rubbish, Debris and Silting

The accumulation of rubbish, debris and vegetation can block channels and screens causing water to back up and overflow the river banks or culverts. It is important that debris and rubbish thrown in or washed into the watercourses from riverside paths is removed on a regular basis.