Drainage Northern Beaches

Usually the slope above sends surface water and groundwater towards the house. An ag drain along the house, or a cut-off drain across the slope above it, catches the water and carries it to a pit.

NSW guides put a subsoil drain, slotted ag pipe in gravel, at about $50 to $150 a metre, a surface channel drain at $100 to $300 a metre, and a small pit-and-pipe stormwater system at $1,500 to $6,000 (The Quote Yard, June 2026). Length, depth, rock, digging under paving and the licensed stormwater connection change the price. Your price is set at the free site visit.

Usually the ground falls the wrong way, the soil under the lawn is compacted, or water from the slope above has nowhere to go. Fixes range from regrading and an ag drain to new pits.

Yes. Gravel backfill, an ag pipe and weep holes stop water building up behind the wall. Without them, water pressure builds up behind the wall after rain.

A licensed plumber or drainer, because stormwater pipes are regulated drainage work in NSW. We can work alongside a plumber where a job needs both.

Often. Ag drains run in narrow trenches, and strip drains can go along the edge of existing paving. We plan the route around plants and paths.

Usually the ground or paving falls towards the house, or a downpipe empties beside it. Regrading so the ground falls away, a strip drain at doorways and connecting the downpipe fix most cases. Garden beds should sit below the weep holes, not banked against the wall.

Natural runoff coming downhill generally has to be accepted. A neighbour shouldn't concentrate or redirect it onto your land with a pipe, new paving or changed levels. Talk to them first; councils step in where a structure directs the water and causes damage.

Usually, yes. Roof water should reach a legal point of discharge, such as the kerb, a council pipe or a drainage easement. A downpipe spilling onto the ground beside the house wets the subfloor and footings. Connecting downpipes is licensed plumbing work.

Sometimes, on deep sand well above the water table. For new roof or paving water, council's policy needs an engineer's design from a soil test, the trench 3 m from boundaries and buildings, and its base 500 mm above the water table. Beside the lagoons, that often rules it out.

It's common on cut sandstone. Groundwater runs along the rock layers and comes out where the slope was cut for the house. It can't be stopped, so it is caught: a spoon drain or ag drain along the rock's base, falling to a pit.

Mostly, yes. Both are a gravel trench with a slotted pipe that collects groundwater and carries it away. In Australia it's usually called an ag drain or ag line. The pipe sits in a filter sock and needs a fall to a pit or another outlet.