Natural Pond Handbook

22 · Waterfalls, Streams & Spillways

Illustration of a waterfall
A level weir and a sheet fall make the classic spill.

Moving water is both beautiful and functional: a waterfall is one of the best aerators you can build. The secret is a level weir and tidy liner folds.

Design basics

  • A wide, low weir (spillway) aerates more than a tall thin fall. A 10 cm drop over 60 cm width beats a 60 cm drop over 10 cm.
  • Plan the stream on paper first; keep it visible from seating areas.
  • Every liner fold must be tucked and weighted so water cannot sneak behind it.

Leveling the weir

Use a spirit level — an uneven lip sends water to one side and looks broken. Build the weir from a solid, level stone or a purpose-made weir box, then pack gaps with foam or silicone-safe sealant.

Liner and rockwork

  1. Line the entire stream bed with EPDM + underlay, extending well past the banks.
  2. Create pools at each step so water does not free-fall onto bare liner (which erodes and looks unnatural).
  3. Set rocks so they hide the liner edge; secure with a little spray foam underneath to stop shifting.
  4. Backfill behind rocks with soil so the stream reads as part of the landscape.

Pump sizing for lift

required_flow = visual_desire + head_penalty Total head = vertical lift + ~0.3×pipe_length + friction from bends Read the pump curve at YOUR head, not the box headline.

Common leaks

  • Water escaping behind the liner at the top edges — fix by extending/weighing the liner.
  • Perforated liner from sharp rock — always use underlay.
  • Undersized pump causing trickle instead of sheet — increase flow or narrow the weir.
Bio-film bonus The wet stream surfaces grow a slime of beneficial bacteria that further polishes water — a stream is a filter as much as a feature.
Waterfall construction steps
  1. Shape the cascade during excavation — build shelves, not a smooth slope.
  2. Lay underlay and liner up the entire waterfall path, overlapping the pond liner by 300 mm minimum.
  3. Build each lip with flat stone. The lip must be perfectly level or water will channel to one side.
  4. Use expanding foam behind each lip to force water forward over the stone, not behind it.
  5. Test with a hose before backfilling. Adjust stone until water flows evenly across the full width.
Sound control A wide, shallow cascade over flat stone makes a gentle trickle. A narrow, deep drop over rough stone makes a loud splash. Design the cascade profile to match your noise preference.