Retaining Walls in Kanimbla

Kanimbla sits on the slopes below the range on the western edge of the city, and its blocks are among the steeper suburban blocks in Cairns. The estates here were cut into the hill, which leaves most properties with a substantial batter or wall behind the house and a fall away from it at the front.

The volume of water off the range

Every hillside suburb deals with runoff from above. Kanimbla deals with runoff from a genuinely large catchment, because the ground above it keeps going up into the range.

During sustained rain that produces flows that have nothing in common with what a suburban block generates on its own. The practical consequence for retaining is that a wall here needs to be considered as part of a drainage system rather than as an isolated structure. Where the water arrives from, what path it takes across the property now, and where it is going to end up are the questions that come before what the wall is made of.

Surface interception above the wall matters as much as subsoil drainage behind it. A cut-off drain across the top of a batter, taken to a proper discharge, removes a large part of the load before it ever reaches the wall. Without it, the subsoil drain behind the wall is trying to handle water that should never have got there.

The discharge point is the constraint that shapes everything. On a steep block the water has somewhere to go, which is an advantage, but it has to be taken there deliberately rather than allowed to find its own way, and it cannot simply be delivered onto the neighbour below.

Tall walls, and what that triggers

The retained heights here are frequently above the threshold where engineering and approval come into it, and often well above. That is not a complication to work around, it is simply what the ground requires, and a wall of that height built without design is a genuine risk rather than a paperwork failure.

Where the required height is substantial, terracing into two or more walls is worth pricing against a single tall wall. It is often cheaper, it can keep individual walls under the certification threshold, and it produces more usable ground. Whether it works depends on having the depth of block to step back into, which not every property here has.

Terraced rear yards

The other common job in this suburb is converting a steep rear yard into usable levels. On a block with real fall, that is the difference between a backyard and a view of a slope.

The planning question is what each level is for before any wall line is set, because on a steep block the depth of each terrace is won expensively and a terrace too narrow to use is money spent for nothing.

Call 0468 066 055 and describe how much fall you have across the block.