Two-Tier Hillside Pond: Gravity Flow, Barrel Biofilter & Builder's Bible

240-gal lower + 160-gal upper (20 ft above), stream between, ½-barrel biofilter — needs gravity flow design, not pump pressure.

Key Design Principles

1. Upper pond overflows to stream — weir or standpipe sets level.
2. Stream gradient: 2–3% slope, lined, rocks for aeration.
3. Lower pond receives stream — pump returns to upper pond.
4. Pump in lower pond — pushes to upper, not through biofilter.
5. Biofilter on return line: Pump → biofilter → upper pond.

½-Barrel Biofilter Build

• 55-gal drum, inlet at bottom, outlet at top.
• Media: K1, bio-balls, or lava rock.
• Air stone inside — moving bed = self-cleaning.

Essential Resource

"The Pond Builder's Bible" — covers gravity systems, hydraulics, construction. Library or buy. Copy the gravity-flow chapters.

Frugal Tips

• EPDM liner scraps for stream.
• PVC pipe for plumbing — glue, don't clamp.
• Rocks from property.

Gravity is free. Design for it. The Bible shows how.