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What this layer is
“Wetness” here is a composite view of how waterlogged the ground is, built from three independent sources:
- Topographic Wetness Index (TWI) — a classic hydrological metric derived from the 1-metre LiDAR. At every point on the ground it combines the slope (how fast water drains away) with the area uphill that drains to that point (how much water arrives). High TWI means flat, low-lying ground with lots of upslope catchment — the ground that stays wet longest. Low TWI means dry ridges and well-drained slopes.
- Sentinel-1 SAR saturation — radar from the European Space Agency's Sentinel-1 satellites penetrates cloud and can see waterlogged ground even under vegetation cover. Different from optical satellite imagery (which has to wait for clear skies), SAR gives a year-round signal of saturation.
- Copernicus Water & Wetness — the European Union's High Resolution Layer that classifies every 10-metre square as permanent water, temporary water, permanent wet, temporary wet or dry. A useful coarse-grain check against the other two layers.
Put together, they give a picture that is consistent with what farmers already know from walking their ground in February — but formalised, mapped and measurable.
What it reveals in this catchment
- A classic wet / dry mosaic. The cluster sits on a mix of Hastings Beds sandstone, Wealden clay and alluvial valley-bottom deposits. TWI resolves this into dry sandy ridges, intermediate clay slopes and persistently wet valley bottoms along the ghyll networks.
- Seepage hotspots. Small springs, seepage flushes and iron-rich ghyll heads are common features of the High Weald. The Sentinel-1 SAR signal picks these out especially well in winter and is often the first thing to reveal them on otherwise unremarkable-looking pasture.
- Seasonal winter wet. Much of the cluster's heavy clay land is “wet in winter, workable in summer”. The time series shows the annual cycle and where that cycle is extending (more winter waterlogging) or contracting (summer drying earlier).
- Historic wet features. Crossreferencing wetness with the 1890 OS maps often shows wet areas that were actively managed as ponds, wet meadows or osier beds a century ago and have since reverted to simply wet.
What land stewards can do with this
- Match land use to wetness. Persistently wet ground is generally better as wet woodland, rushy pasture, fen meadow or reedbed than as cultivated land or drained grazing. Knowing which fields sit where on the wetness gradient lets you make that call objectively.
- Target wet-habitat creation. For SFI, Countryside Stewardship or private natural-capital schemes, wet-habitat actions require wet ground. Pointing to high-TWI ground with SAR confirmation is much more fundable than describing it in words.
- Plan drainage honestly. Some wet ground genuinely benefits from drainage maintenance; a lot of wet ground is wet because it wants to be wet, and fighting that is expensive and rarely wins for long. Wetness data helps you tell the difference on your own holding.
- Catch diffuse pollution risks. Wet ground immediately upslope of a watercourse is a diffuse-pollution risk zone. Placing buffer strips, reversion to low-input grassland or wet woodland in these precise locations gets the most water-quality benefit per hectare.
Data sources: Topographic Wetness Index derived from Environment Agency 1 m LiDAR DTM; Sentinel-1 SAR imagery via the Copernicus Data Space Ecosystem; Copernicus High Resolution Layer — Water and Wetness. All processing, compositing and cluster-level time-series by the ecology platform.