Water Environment

The expansion of Heathrow will affect the existing water environment (rivers, lakes and groundwater).

It also offers opportunities for the improvement of the local water environment, through the design of the newly diverted rivers, river improvement works in the Colne and Crane Valleys and the use of new flood storage areas as multifunctional spaces for biodiversity and public open space.

Aspects of our proposals that could cause effects

The new runway and expansion of the apron and taxiways to the west will require the diversion of a number of watercourses in the Colne Valley. This includes the River Colne, Wraysbury River, Longford River, the Duke of Northumberland’s River and Colne Brook.

A number of smaller watercourses will also be diverted or removed to make room for the expanded airport.

In addition to changes to rivers, a number of lakes will be removed to facilitate expansion. The majority of these are along the course of the Colne Brook to the south of the M4. Spout Lane Lagoon (which is part of the current airport drainage system) will also be removed, to make way for the western apron expansion.

There will be changes to groundwater flow pathways in the underlying Lower Thames Gravels aquifer. This is due to the installation of new permanent features in the form of new basements, as well as excavations and dewatering during construction.

The expanded airport will interact with the floodplain, which could affect how the local area responds to flood events. As a result, new areas of flood storage will be provided upstream of the site in the Colne Valley and new surface water drainage and treatment will be provided for the airfield, expanded road network and other development. Flood risk is being considered in great detail to ensure we protect local homes and businesses.

A summary of the effects reported in the PEIR

The majority of effects of the Project on the water environment are not considered significant, as a result of the measures that have been embedded in the design of the Project, and those that will be implemented during construction.

It is expected that there will be a significant negative effect as a result of the infilling of lakes, resulting in a loss of open water and associated habitat. Significant negative effects are also predicted at this stage of the design of the proposals on the Wraysbury River, River Colne, Longford River and Duke of Northumberland’s River as a result of passing the rivers beneath the new runway in the proposed covered river corridor.

There is also the potential for significant cumulative negative effects to the River Colne from the effects of the Project and HS2 which crosses the Colne Valley further north of Heathrow.

Measures for reducing potential effects

The main environmental measures to reduce effects on the water environment include:

  • The design of the covered river corridor under the new runway, including the river channel design and the combination of natural and artificial lighting will be developed to encourage fish and animals to pass through it and plants to grow.
  • Designing the new river channels to be of varying shape.
  • Replacement river flood storage areas upstream of the airport.
  • New on and off-airfield surface water drainage systems will be installed to ensure no effects on water quality and no change in flood risk as a result of runoff from new areas of hardstanding.
  • A programme of river restoration opportunities along the Rivers Colne and Crane to provide compensation for the net loss of river length in the Colne Valley that will occur as a result of river channels being diverted and combined.
  • Water management activities in the construction phase to capture and treat water from construction excavations and surface water run-off, before being released to the environment.

Have your say

We want to know what you think about our proposals to manage the environmental effects of expansion and, in particular:

  • whether there are any other initiatives or proposals that we should consider to address the emissions from airport related traffic or airport operations;
  • our proposals to help health and well-being, in particular whether there are any proposals that you think we should consider to address the effect of the Project on the health and wellbeing of our colleagues, neighbours and passengers;
  • our noise insulation schemes;
  • what factors are most important as we develop our proposals for noise management, in particular our proposals for the design and implementation of a noise envelope;
  • our proposals for maximising new jobs and training, in particular, whether there are any other ways that we can maximise skills and training opportunities to benefit our local communities;
  • on our approach to addressing effects on the historic environment, including any particular proposals you would like us to consider.

To respond to our proposals please answer the overarching question on the Environmental Introduction page.

View next topic in this group: