When a pool is removed from a property, the drainage pattern of the backyard changes. The pool was a significant surface water interceptor, rain falling on the pool deck and into the pool was managed by overflow drains and the pool’s own outlet. Once the pool is gone, stormwater that previously went into the pool now needs somewhere to go. Getting the drainage design right after pool removal prevents the most common post-removal complaint: a waterlogged, boggy area where the pool used to be.
Quick Answer (BLUF)
After pool removal, the former pool site must be regraded to ensure surface water flows away from the filled area and toward appropriate drainage outlets. In clay-heavy Southern Highlands soils, subsurface drainage within the fill is also important to manage groundwater and seasonal saturation. Poorly designed post-removal drainage is one of the most common causes of long-term settlement problems and waterlogging on former pool sites. A good contractor should include surface drainage design in their scope.
Why Stormwater Management Changes After Pool Removal
Before removal, a typical pool acts as a stormwater collector:
- Pool deck rain runs into the pool or to the pool’s deck drains
- Overflow from heavy rain goes through the pool’s overflow outlet to stormwater
- The pool water level is managed by the filtration system
After the pool is removed and the site backfilled:
- The former pool footprint is now a below-grade filled excavation (or at grade if the fill was raised to match surrounds)
- Rain falling on the site needs clear surface drainage paths
- Groundwater in the surrounding soil now has one fewer outlet (the pool body)
- The fill material may have lower drainage capacity than the surrounding native soil
In the Southern Highlands context, this is particularly important because:
- The region receives 700-1,500mm annual rainfall depending on location
- Clay soils hold moisture and have poor natural drainage
- Winter rainfall is prolonged and heavy in Robertson, Bundanoon, and escarpment areas
- Frost events can seal the surface temporarily, concentrating runoff
Surface Grading: The First Priority
After backfill is complete, the surface of the former pool site should be graded to:
- Slope away from the house, the primary principle of residential site drainage is that water should flow away from all habitable structures
- Slope away from the fill zone, the filled excavation should not be the low point that collects water from surrounding areas
- Connect to existing drainage outlets, whether that’s an existing subsoil drain, a surface channel, the street kerb and gutter, or a garden drainage point
Minimum fall on grass or garden surfaces: 1:100 (1cm per metre) for lawns, up to 1:40 (2.5cm per metre) for paved surfaces.
In practice, many pool removal backfill sites need some top-fill adjustment after initial settling (usually within 1-3 months) to achieve the final drainage gradient. Budget a small amount for top-up fill and regrading post-settlement.
Subsurface Drainage Within the Fill
For the Southern Highlands’ clay-dominant soils, surface grading alone is often insufficient. Groundwater and soil moisture within the fill zone can create a perched water table, a saturated zone within the fill that doesn’t drain to the surface or to underlying natural drainage.
The solution is subsoil drainage within the fill:
- Agricultural drainage pipe (slotted or perforated UPVC) laid at the base of the fill or at intervals within the fill
- Drain pipe bedded in clean gravel wrap (drainage aggregate)
- Pipe connected to a discharge point (subsoil drain outlet, detention basin, or garden drainage pit)
This subsurface drainage system allows water that infiltrates the fill to drain laterally rather than pooling within the fill zone. It’s standard practice on good-quality pool removal jobs and should be specified in the backfill scope.
Connecting to the Property’s Existing Stormwater System
Where the property has existing stormwater infrastructure (roof drainage gutter outlets, paved surface drains, etc.), the post-pool drainage should connect logically to this system.
In older Bowral, Mittagong, and Moss Vale properties, the stormwater drainage may be:
- Connected to the street kerb and gutter via a stormwater pipe
- Directed to a garden soakage pit
- Not formally documented (many older properties have informal drainage)
If your property connects to Council stormwater infrastructure, confirm that post-pool drainage can connect appropriately. In some cases, the pool’s overflow drain was the only formal stormwater connection for the backyard area, when the pool goes, a new drainage point needs to be established.
Common Drainage Problems After Pool Removal
| Problem | Cause | Solution |
|---|---|---|
| Boggy patch in former pool area | Poor subsurface drainage in fill | Install subsoil drainage; improve fill material |
| Ponding after rain | Surface not graded to drain | Regrade surface; add top fill to reshape |
| Water tracking toward house | Fill surface lower than surrounding ground | Regrade fill to direct water away |
| Soggy lawn that doesn’t dry out | Clay fill retaining moisture | Install subsoil drainage; top with sandy loam topsoil |
| Fence posts rotting faster than expected | Fill retaining water around fence footings | Drainage improvement around fence line |
Drainage Considerations for Specific Southern Highlands Locations
Moss Vale (low-lying areas near Wingecarribee River): Properties in flood-adjacent or low-lying areas need drainage that accounts for periods of elevated groundwater. Agricultural drainage within the fill is particularly important here, along with ensuring the fill is at least level with (or above) the surrounding ground to prevent pooling.
Robertson (high rainfall zone): Robertson receives 1,300-1,500mm annually. Drainage design for Robertson pool removal sites needs to handle intensive rain events without the fill becoming saturated. Coarse granular fill (not site clay) and well-designed subsoil drainage are essential.
Bundanoon (frost and frozen ground): Frost events temporarily seal the surface and concentrate runoff during thaw periods. Drainage design should account for these thaw-flow events, ensuring the fill surface can handle the sudden surge.
Rainwater Harvesting Opportunity
When redesigning drainage after pool removal, consider whether rainwater harvesting can form part of the post-pool drainage design. The former pool area, properly piped, can direct roof runoff to an above-ground rainwater tank or underground cistern, converting a drainage challenge into a water supply asset.
The guide on pool removal and rainwater harvesting covers this option in detail, including tank sizing, pump systems, and appropriate uses for harvested water.
What Your Pool Removal Contract Should Say About Drainage
When reviewing pool removal quotes, look specifically for drainage provisions:
| Item to Check | What to Look For |
|---|---|
| Surface grading after backfill | ”Site graded to drain away from structures and to existing drainage” |
| Subsoil drainage within fill | ”Agricultural drain installed at base of fill, connected to [point]“ |
| Top soil quality | ”150mm topsoil placed over compacted fill, suitable for lawn establishment” |
| Drainage connection | ”Existing stormwater connection maintained / new drainage point installed” |
If the quote says nothing about drainage, ask specifically. Post-removal drainage is not an optional extra, it’s a fundamental part of restoring the site to functional condition.
Frequently Asked Questions
Why is my former pool area boggy after the removal was done? Likely causes: the fill material has poor drainage characteristics (site clay used instead of granular fill), no subsoil drainage was installed within the fill, or the surface wasn’t graded away from the filled area. In most cases, a combination of additional subsoil drainage and surface regrading can fix this.
How much does it cost to fix drainage problems after pool removal? It depends on the extent of the problem. A surface regrading with additional top fill: $1,000 to $3,000. Installing subsurface drainage in an already-filled site: $2,000 to $6,000 (requires some excavation to install drainage pipes). Addressing this correctly at the time of pool removal is far cheaper.
Can I use the pool’s existing overflow drain for the backyard drainage after removal? Sometimes. If the pool overflow outlet connects to stormwater infrastructure, it may be possible to retain and repurpose it as a subsurface drainage outlet for the backfilled area. Discuss this with your contractor at the design stage.
Will the drainage change if I plant a garden on the former pool site? Yes, plant root systems eventually improve drainage by creating channels in the soil. But root drainage takes years to develop. In the first 2-3 years, engineered drainage within the fill is much more important than planting choices.
Does Wingecarribee Council have specific stormwater requirements for pool removal sites? The council’s general stormwater management requirements apply, primarily that drainage must not direct water onto neighbouring properties or create flooding. Specific post-removal drainage design is typically addressed in the pool removal approval conditions and through the certifier’s sign-off process.
For pool removal with comprehensive drainage design and grading in the Southern Highlands, contact Southern Highlands Pool Removals for a site-specific quote.