Surface Water Catchment and Sinkhole Study

As part of the Mining Plan, AR3 are required to evaluate the effects of mining on existing water users in accordance with Term of Reference 006 and the requirements of the Mining Act 1971 (SA).

During early consultation with landowners, surface water depressions (described locally as sinkholes, runaway holes and swamps) were raised as important sources of water. The depressions receive water when ground conditions become saturated and surface water flows to the depression features. Some depressions contain a permeable limestone base, and hence, when they receive surface water, seepage can occur to the underlying aquifer.

Report Aims

Confirm the location and number of depressions in proximity to the proposed ML.

Identify which depressions are locally important to landowners, including documenting their uses.

Assess whether depressions are likely to be important with respect to groundwater recharge.


A desktop review of publicly available literature on the subject of depressions and sinkholes in the Lower South East of SA.

Using the site digital terrain model, identify and map depressions within the proposed ML area including their surface water catchments.

Meet with landowners to determine how depressions are used as a water supply source. Document any identified recreational or aesthetic values the depressions have.

Sample and analyse water from depressions and compare their hydro-chemical characteristics to regional groundwater.

Provide a first order estimate of recharge from the depressions to local groundwater and estimate their magnitude on the local groundwater balance.

Report on the above to clarify the importance of depressions as water supply and recharge sources.


Literature reviews were undertaken to document studies on depressions and sinkholes and assess their importance to recharge processes. Whilst studies were limited in number, there is general agreeance that recharge via point sources (in the region of interest) contributes only minor amounts of recharge on an annual basis. This is largely due to depressions and sinkholes having small, localised surface water catchments with limited runoff reporting to sinkholes.

Based on the latest Water Allocation Plan (South East Landscape Board, 2019) the Comaum GMZ has a calculated recharge value of 50 mm/annum.

Herzeg and Leaney (1993) identify that depressions with small catchments sizes, annual recharge for point sources likely only contributes around 1.4 mm/annum to the Tertiary Limestone Aquifer. Thus, comparisons can be made with respect to total recharge volumes between diffuse and point sources at the proposed ML. Table 5.1 in the report provides estimated recharge volumes under a range of recharge amounts. As seen from Table 5.1, point source recharge is likely to be less than 5% of annual recharge per annum, assuming recharge of around 50 mm is adopted. If smaller recharge volumes are adopted (10 mm/annum) then the percentage could increase to around 14%.

Nonetheless, evidence from the ML (catchment sizes and hydrochemistry) indicates that point source recharge is likely a small contributor to the local water balance.

Diffuse vs Point Source Recharge at the proposed ML