Guide·me
lakes-hydro-lab · v0.1 · 7-step layer tour
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The dashboard has nine layers. Turning them all on at once is overwhelming — and not useful. This guide walks through the order that actually tells the story: terrain → drainage → flood-prone zones → orientation → population → validation against real history. Five steps to get the picture; two more to compare alternatives.

STEP 01

Start with terrain alone

Step 1: hillshade only
ON: DEM hillshade
OFF: everything else

The bare relief. EA 1 m LIDAR Composite rendered as a north-west-illuminated hillshade. See the shape of Cumbria — Skiddaw + Bassenthwaite north; Buttermere + Wasdale west; Scafell central; Helvellyn + Ullswater east; Eden basin to the north-east; coastal plain west.

The dark voids around the edges are where LIDAR doesn't cover — Solway Firth (NW), Irish Sea (W), Pennine fringe (E).

Why start here: orientation. Once you can see the shape of the land, everything else makes sense.
STEP 02

Add HAND — where water naturally collects

Step 2: + HAND standard
ON: DEM hillshade + HAND standard
OFF: everything else

HAND (Height Above Nearest Drainage, Nobre et al. 2011) tints each cell by how high it sits above the nearest stream.

Yellow valleys = at or near channel level (potentially flood-prone). Orange / brown = mid-slopes. Purple ridges = upland, hydrologically safe.

Channel-init threshold: 0.025 km² (2.5 ha) — chosen empirically against real-world river networks; defensible for UK flood mapping.

The 35 % limit: HAND only exists where a cell's downhill flow path reaches a stream within the map's 65 × 65 km extent. Lowlands that drain off-map (lower Eden valley draining north past Carlisle) show no HAND — that's the algorithm being honest, not failing.
STEP 03

Add lakes — anchor recognition

Step 3: + Lakes
ON: DEM + HAND + Lakes & water
OFF: everything else

Add the lakes. Bassenthwaite, Derwentwater, Buttermere, Crummock, Wast Water, Loweswater, Ullswater, Thirlmere, Coniston, Windermere — instantly the map becomes readable for anyone who knows Cumbria.

Source: OpenStreetMap natural=water polygons (ODbL). 2,209 lake + tarn polygons within the extent.

Cross-check: lake surfaces should show HAND ≈ 0 (they ARE the local channel). Visual confirmation the algorithm got the easy case right.
STEP 04

Add towns — population context

Step 4: + Towns
ON: DEM + HAND + Lakes + Towns & built-up
OFF: everything else

Now the question stops being abstract. Cockermouth, Keswick, Workington, Whitehaven, Egremont, Penrith, Kendal, Ambleside, Windermere, Bowness — the towns at risk.

Brown polygons = OSM residential/commercial/industrial footprints (built-up land). Black-edged dots = named place centroids; major towns labelled at all zooms, villages appear when zoomed in.

The flood-risk question becomes visual: wherever a yellow HAND zone overlaps a brown town footprint, that's a population-at-risk hotspot.
STEP 05

Add historic floods — does the prediction match reality?

Step 5: + Historic floods
ON: all of the above + Historic floods

EA Recorded Flood Outlines (OGL v3) — actual flooded extents from the EA's records. 901 polygons across 348 events within Cumbria, including:

• Cockermouth November 2009 (the catastrophic flood that triggered the EA's modern flood-defence rebuild)
• Storm Desmond December 2015 (Carlisle, Keswick, Kendal — 65 flooded areas in one event)
• Storm Dennis 2020, Storm Ciara 2020, Storm Henk 2024, Brigham 2025

Major 2009 + 2015 events are styled darker red and slightly more opaque. Hover any polygon for event name and date.

The whole point: wherever red flood polygons overlap yellow HAND zones, the LIDAR-derived prediction matches the historical record. Where they disagree is where the science is interesting.
STEP 06

Compare HAND densities (advanced)

Step 6: HAND dense comparison
SWAP: HAND standard off, HAND dense on

Lower the channel-init threshold from 0.025 km² → 0.01 km². More streams, more cells with HAND (45 % of land vs 35 %). The trade-off: small drainage ditches start to be counted as channels, so some areas of the lowlands are visibly over-extracted.

Toggle between them to see the genuine uncertainty in WHERE the algorithm draws the line.

For most users: stick with the standard 0.025 km² layer. The dense layer is for researchers who want to see what's under the threshold.
STEP 07

Streams — what HAND is computed from

Step 7: Streams only
ON: DEM hillshade + Streams
OFF: HAND, everything else (so you can see the channels clearly)

The extracted drainage network. Every blue line is a cell where the flow accumulation exceeds the 0.025 km² channel-init threshold. The blue web you see is what HAND measures distance to.

Compare against your mental map: Eden, Cocker, Derwent, Greta, Kent, Lune, Esk, Mite, Calder, Ehen, Bleng — all there.