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What this layer is
Flood risk in England is modelled nationally by the Environment Agency and published as a series of open datasets. Three are most useful at cluster scale:
- Flood Zone 2 and 3 — the statutory fluvial flood maps. Zone 3 is land assessed to have at least a 1 in 100 annual chance of river flooding (or 1 in 200 for coastal). Zone 2 is the wider area with a 1 in 1,000 chance. These are the zones used in planning decisions.
- Risk of Flooding from Surface Water (RoFSW) — models what happens when heavy rain overwhelms drains, soils and small watercourses. Usually a better predictor of what will actually flood on a given farm than the fluvial maps, especially in the headwaters.
- LiDAR-derived pooling and flow-accumulation — derived from the 1-metre DTM (see the terrain page). Reveals the small hollows, compacted tracks and ditch networks that collect water even in the absence of a named river.
What it reveals in this catchment
The Upper Medway is headwater country. Statutory Flood Zone 3 covers a relatively small proportion of the cluster area — this far up the system there is simply not yet enough water in the main channel for large fluvial floods. But that modest statutory risk hides two more important patterns:
- Surface water risk is material. RoFSW maps pick out tracks, ghyll heads, compacted field margins and road drainage pinch-points where heavy rain produces real problems. The cluster's ghylls concentrate flow very quickly when the soil is saturated.
- What we do here matters downstream. Even if fluvial flood risk on cluster holdings is modest, the cluster sits above thousands of hectares and several villages along the Medway. Natural flood management at the headwaters — slowing, spreading, storing — has downstream benefits disproportionate to the land committed.
- Historic water management features exist. Old mill leats, hammer ponds, stew ponds and boundary ditches from centuries of Wealden iron and mixed farming still shape how water moves today. Some are working with us, some are working against us. LiDAR helps identify which.
What land stewards can do with this
- Slow the flow. Leaky woody dams in small ghyll streams, restored ponds, scrapes, and wet-woodland creation at flow-accumulation hotspots all slow water in the upper catchment. Small interventions at the top of the system are worth many times their size in downstream benefit.
- Manage saturated-ground ponding. Field corners and track lows that show on the surface-water maps are candidates for buffer strips, temporary attenuation features or even permanent pond creation.
- Fund the work through flood schemes. Natural flood management is an increasingly well-funded area of public and private investment. A cluster-scale plan, backed by EA flood data for credibility, is much more fundable than a single-farm proposal.
- Protect your own infrastructure. Knowing exactly where surface water collects lets you design track layouts, gateway placement and low-input crop choices that avoid the worst spots.
Data sources: Environment Agency Flood Map for Planning (Rivers and Sea) for Flood Zones 2 and 3, and the EA Risk of Flooding from Surface Water dataset. Flow accumulation and pond detection from EA 1 m LiDAR, processed by the cluster's ecology platform. All EA data is Open Government Licence.