Flood Defence (Mitigation) Strategy

Where flood risk cannot be avoided through layout and levels alone, it has to be actively managed. A flood defence and mitigation strategy sets out how a site, building or community will be protected — combining the right measures, at the right scale, to keep people and property safe without increasing flood risk elsewhere. Water Environment has extensive experience planning and designing Environment Agency-approved flood defences for riverside and coastal schemes, including large, technically challenging projects that are now built and protecting hundreds of homes.

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Managing flood risk: the hierarchy

Good flood management follows a clear order of preference. We work through it with you to arrive at a proportionate, deliverable strategy:

Avoid — locate and lay out development away from the highest-risk land, and raise finished floor levels above the design flood level wherever possible.
Manage and mitigate — where some risk remains, reduce it with defences, flood storage, resilient construction and safe access.
Respond — for any residual risk, plan for it with flood warning and evacuation procedures so people can act safely when a flood is forecast.

A mitigation strategy almost always blends several of these measures rather than relying on a single defence. We make sure the combination is technically sound, acceptable to the regulators, and viable to build and maintain.

Flood defence scheme layout plan for the Hoe Valley scheme, Woking

Mitigation measures we design

The right measures depend on the source of flooding, the value and vulnerability of what is being protected, and whether we are working with a new development or an existing building. We design and specify:

Measure	What it does
Walls and embankments	Permanent raised defences along a watercourse or coast that hold back flood water to a defined standard of protection.
Raised levels and thresholds	Setting finished floor levels, access routes and key thresholds above the design flood level, including a climate change allowance.
Flood storage and floodplain compensation	Replacing lost flood storage on a like-for-like basis so the scheme does not displace water onto neighbours — delivered through coordinated earthworks design.
Property flood resilience and resistance	Retrofit measures — barriers, flood doors, airbrick covers and resilient internal finishes — that keep water out of existing buildings or limit the damage when it gets in.
Safe access and egress	Dry or safe routes in and out during the design flood, supported where needed by a flood warning and evacuation plan.

Construction of flood defences during the Hoe Valley scheme, Woking

Scheme-level flood defences

For larger riverside and coastal schemes we plan and design strategic flood defences end to end. We are involved throughout the process — from early technical negotiations, through the required assessments and full detailed hydraulic modelling, to the detailed design of the defences themselves.

Every defence has to demonstrate that it provides the required standard of protection, performs safely in extreme events including overtopping and breach, and does not increase flood risk to third parties. We design to satisfy the Environment Agency and to secure the Flood Risk Activity permits and consents the works require.

Retrofit defences for existing buildings

Not every flood problem is a new development. Many of our clients own or operate buildings that already flood, or sit behind defences that no longer provide an adequate standard of protection. For these we design retrofit, property-level schemes that protect what is already there.

We have delivered retrofit flood defences for commercial premises and residential properties across the country — including a programme of high-street retail stores and houses in west London — assessing the flood mechanism at each site and specifying a tailored package of resistance and resilience measures. Retrofit work demands a pragmatic approach: the protection has to fit around an occupied, operating building, be straightforward to deploy, and stand up to the way the building actually floods.

Stakeholder engagement and approvals

Flood defence schemes rarely succeed on engineering alone — they need the support of the people they affect. We regularly represent our clients publicly at scheme exhibitions and can lead negotiations with key stakeholders, landowners, and concerned residents or neighbours.

We manage the technical relationship with the Environment Agency and the Lead Local Flood Authority from the first pre-application discussion through to sign-off, presenting the modelling and design evidence that underpins the strategy and resolving objections before they hold up consent.

Flood defence and mitigation works at Wallis Road

How we work

Risk appraisal — we establish the source, mechanism and severity of flooding at the site, drawing on flood mapping, historical records and, where needed, bespoke hydraulic modelling.
Options and strategy — we work through the mitigation hierarchy to identify the measures that protect the site to the required standard, and test them for cost, buildability and regulatory acceptability.
Detailed design — we design the chosen defences and produce the drawings, calculations and supporting assessments needed for planning and for Environment Agency consent.
Consents and permits — we prepare and submit Flood Risk Activity permit applications and discharge the relevant planning conditions.
Engagement and delivery — we represent the scheme at exhibitions and stakeholder meetings and provide technical support through construction.

Why Water Environment?

Our directors have a combined 40+ years of specialist experience in flood risk, hydrology and the design of flood defences. Because we model the flooding, design the defences, and shape the earthworks and river works that go with them, our mitigation strategies are joined-up rather than handed between disciplines. We work across all of England and Wales and have delivered Environment Agency-approved schemes that now protect hundreds of homes.

We are members of the Chartered Institution of Water and Environmental Management (CIWEM) and hold professional qualifications with the Institution of Civil Engineers (ICE).

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