Flood Risk Management in Herne Hill and Dulwich

Why is this scheme necessary?

We are working on a flood alleviation scheme to benefit the Dulwich and Herne Hill areas in the event of extreme weather experienced over a short period of time.

In the event of extremely heavy rainfall, it will reduce the risk of surface water and sewer flooding. In the past, flooding has caused significant disruption and damage to local properties. In 2004, severe flooding resulted in damage‐related insurance claims totalling over £1million; and investigations show that the area continues to be at a higher risk of flooding compared to other parts of Southwark.

What is causing the flooding?

• The ‘lie of the land’: Herne Hill and Dulwich are located within the valley of the River Effra catchment. Whilst the river is no longer present as a watercourse, surface water from heavy rainfall will still naturally migrate towards these areas as they remain low lying. • Saturated green spaces: As London has become densely populated, green spaces such as gardens and parks act as big sponges for rainwater but in very heavy rain these can quickly become saturated creating a ‘run off’ of excess water. • Sewer inundation: In very heavy rain, surface water inundates the sewer network to cause sewer flooding.

What are we doing?

In consultation with the local community, we are investing in flood alleviation measures, which will take place in Dulwich Park, Belair Park and Dulwich Sports Ground. These measures include:

• Building barriers or earth bunds which can temporarily contain or redirect surface water into existing water sources, for example lakes and ponds. • Increasing storage capacity of existing water bodies. • Constructing below‐ground storage areas to provide further capacity to store flood water and provide an efficient outflow route from the park for storm water; the stored water is then released gradually back into the sewer network reducing the risk of sewer flooding. • Planting wetland wildflower meadows to attract wildlife, enhancing local habitats and biodiversity.

By applying a sustainable, low impact approach to flood risk management, the flood alleviation scheme’s design is innovative. It will deliver numerous environmental benefits as well as economic value to the surrounding community by reducing the risk of flooding to homes and businesses.

8th April ‐ FINAL Southwark Council is responsible for managing the risk of flooding from surface and ground water in the borough. Thames Water is responsible for maintaining the sewer network across London. Together Southwark Council and Thames Water are working in partnership, with the support of the Environment Agency, to deliver this Flood Alleviation Scheme.

8th April ‐ FINAL