Infiltration Testing for Bendigo: Porchet & Double-Ring Methods

The alluvial flats of Epsom and the clay-rich slopes of Kangaroo Flat rarely share the same subsoil story. In Bendigo, soil permeability can shift dramatically within a single block — a fact that makes the infiltration test an essential tool for any project involving stormwater management or on-site wastewater disposal. The double-ring infiltrometer, in particular, isolates vertical flow from lateral spread, giving engineers a realistic infiltration rate rather than an optimistic guess. For residential subdivisions near Lake Weeroona or commercial developments along the Mitchell Street corridor, this test provides the hydraulic conductivity data that AS 4678 and local council guidelines demand. Before finalising drainage layouts, many geotechnical teams pair this test with a georradar scan to map preferential flow paths in the underlying soil profile.

Illustrative image of Infiltration test (Porchet/Double-ring infiltrometer) in Bendigo

A single infiltration test in Bendigo can reveal permeability differences of two orders of magnitude between a dry summer profile and a saturated winter one.

Method and coverage

Bendigo’s climate — with hot, dry summers and winter rainfall averaging 500 mm annually — produces seasonal moisture cycles that directly affect infiltration rates. A test performed after a dry February will yield different results than one conducted in a wet August. That is why the Porchet method, dug as a borehole and filled to measure drawdown, works well for shallow drainage assessments in residential blocks around Strathdale. For larger infiltration basins or detention systems serving commercial lots, the double-ring infiltrometer is preferred because it maintains a constant head and minimises edge effects. The procedure follows the AS 1289.6.8.1 standard, and the field data is later correlated with laboratory results from a permeability test in the lab to confirm consistency across scales. Field crews also log soil texture, compaction state, and root channels — all factors that influence the final design infiltration rate.

Regional considerations

The field technician sets up the double-ring infiltrometer on a level bench of soil near the proposed drainage line. A steel ring is driven 150 mm into the ground with a drop hammer — no mechanical excavators needed, just steady manual force. The outer ring is filled first to create a buffer zone, then the inner ring is maintained at a constant water level using a Mariotte bottle. If the soil in Bendigo has high clay content, the infiltration rate may drop below 10 mm/h, which triggers the need for alternative drainage strategies. In those cases, the team often recommends supplementary drenes verticales to accelerate consolidation or a surface drainage redesign to avoid ponding against building foundations.

Reference parameters

Parameter	Typical value
Test method	Porchet (falling head) / Double-ring infiltrometer (constant head)
Standard reference	AS 1289.6.8.1, AS 4678-2002
Typical ring diameter	300 mm inner ring, 600 mm outer ring (double-ring)
Measured parameter	Saturated hydraulic conductivity (Ksat) in mm/h
Test duration	2 to 6 hours per location depending on soil type
Reporting	NATA-endorsed report with raw data, field log, and design recommendation

Complementary services

Double-Ring Infiltrometer Testing

NATA-accredited constant-head testing using 300/600 mm rings. Suitable for retention basins, bioretention systems, and large-scale drainage designs. Includes field log, soil description, and Ksat calculation.

Porchet Borehole Infiltration Test

Falling-head method for shallow assessments in residential subdivisions and septic system approvals. Cost-effective for single-lot evaluations in Bendigo's clay soils. Results reported with site-specific recommendations.

Permeability Correlation & Reporting

Field infiltration data correlated with laboratory permeability tests for cross-validation. Deliverables include a certified report with design infiltration rates, seasonal correction factors, and council-compliant documentation.

Q&A

How long does an infiltration test take on a typical Bendigo residential block?

A standard double-ring infiltrometer test takes between 2 and 6 hours per location, depending on the soil type and saturation level. Sandy soils near the Bendigo Creek dry quickly and yield results in the lower end of that range, while the heavy clays around White Hills may require a full day due to very slow infiltration rates.

What is the difference between the Porchet method and the double-ring infiltrometer?

The Porchet method uses a single borehole filled with water to measure the falling head, which is simpler and faster but can overestimate vertical infiltration if lateral flow is significant. The double-ring infiltrometer isolates the inner test area with an outer buffer ring, eliminating lateral divergence and providing a more accurate saturated hydraulic conductivity for design purposes.

Do I need council approval before conducting an infiltration test in Bendigo?

Yes. The City of Greater Bendigo requires a site assessment for any development involving on-site wastewater disposal or stormwater detention. The infiltration test results must be submitted as part of the planning permit application. We handle the notification process and provide a NATA-endorsed report that meets council standards.