Water bodies & SuDS

Every UK scheme has to deal with the rain that falls on its roofs and roads. The 💧 Water tool draws the pond or basin that does it — with real depth, side slopes and storage volume, measured off the shape you draw.

Drawing one

Pick a type from Water ▾ and click round the outline; double-click or press Enter to close it. What you draw is the top of bank — the line that appears on the plan and that houses, roads and parking keep clear of. The banks slope inward from there, so the base is smaller than the outline: a 1.5 m deep basin at 1:3 pulls in 4.5 m on every side.

• Attenuation basin — dry between storms, grassed, doubles as open space. The common choice.
• Retention pond — a permanent water level with storm storage above it. Only the storage above normal water level attenuates; the standing pool is already full when the rain arrives.
• Ornamental lake — a visual water body, with its storage still counted if you want it.

Click a body to select it — drag it whole, drag a corner to reshape, click an edge to add a corner, Alt-click a corner to remove one, and lock it so the generator and your own edits leave it alone.

Right-click a body and choose 💧 Edit… to select it and open the Water & drainage panel on that body — the quickest way back to its depth and slopes once you have closed the panel. Right-clicking also makes that body the selection, so Lock and Delete in the same menu act on the water you are pointing at.

The Water & drainage panel

Set depth, water depth (permanent water above the base — zero for a dry basin) and side slope, and the panel shows live: crest and base area, storage volume, permanent water, total excavation, and the batter width the slopes consume. At the top it shows the scheme's balance — storage provided against storage needed, derived from the impermeable area your own layout has created: roofs, carriageways, footways and driveways, all measured off the drawing.

If a body is too small for its own side slopes — the banks meet before they reach the bottom — the panel and the plan both say so, and name the width it would need.

What it changes elsewhere

• Layout — houses, roads and parking are kept out, like a building or green area.
• Appraisal — the cost of attenuation stops being a per-plot allowance and becomes your measured volume, plus earthworks, lining and marginal planting. Any shortfall is still priced, because it has to be built below ground somewhere. A scheme with no water drawn keeps the old allowance exactly as before.
• Compliance — the Checks overlay gains a Water & SuDS group: side slopes against the standard, basin depth, permanent-water depth, distance to the nearest dwelling, and the storage balance.
• 3D — the bowl is cut into the ground with sloping banks, and wet types get a reflective water surface at the normal level.
• Exports — a WATER layer in the DXF with area and volume text, and the outline in the Revit model.