Role of floodplain woodlands in reducing flooding

Flood flow through woodland
Standing trees, fallen logs, branches and leaf litter form a very dynamic and complex network of multiple channels and dams, which help to slow down flood flows

Although most of Britain’s original floodplain woodland has been lost due to past river engineering and land reclamation works, there is good evidence to suggest that it could have an important role to play in ameliorating downstream flooding. This is based on woodland’s greater hydraulic roughness compared to other vegetation types, which acts to slow down and thus potentially reduce flood peaks.

Unfortunately, floodplain woodlands also pose a number of risks for flood defence. These include enhanced upstream flooding due to the backing-up of floodwaters, restricted access to river banks for flood defence works, loss of engineered flood control, and increased downstream flooding caused by large woody debris blocking bridges and other structures.

A major element of our forest hydrology programme is to evaluate the effects of floodplain and riparian woodlands on flood flows. Studies include:

Restoring floodplain woodland for flood alleviation

The final report on this Defra funded project was published in July 2008. The work provides further support for the potential of floodplain woodland to alleviate downstream flooding.

Restoring floodplain woodland for flood alleviation (PDF-1974K)

Unfortunately, it proved not possible to plant floodplain woodland at the selected sites and the project had to be curtailed. Lessons learnt and recommendations for future work are set out, including the need for one or more replacement demonstration sites to be established to communicate and explain the benefits of floodplain woodland for flood alleviation.