SERIC

Depth to Water Table

A requirement of recently revised Water Allocation Plans prepared by SERIC partner DWLBC was to critically analyse the depth to water table and groundwater recharge rates in relation to various land uses. Available depth to water table data could not adequately meet these needs and it was realised that a radically different depth to water table plan was required to allow more accurate assessment to be made.

Previous depth to the water table plans have been compiled using the well data contained on the government drill hole database SAGeodata, and are compromised by the location of each well in relation to geomorphic features. For example a dune range may have only one or no wells located inside its boundaries and so the contour plan does not show the extent of deeper water levels underlying dune structures.

DWLBC enlisted the help of SERIC to develop a plan that would more accurately show the depth to the water table in all parts of the southeast. To undertake the study SERIC first derived two grid model surfaces across the southeast:

• A Ground Surface model based on existing 10m topographic contour elevations and spot heights.
• A Reduced Water Level surface model extrapolated from wells monitored during the prescribed period between 2004 and 2005.

The Reduced Water Level surface was then subtracted from the Ground Surface to derive a new Depth to Water Table surface. Although not perfect due to the constraints of the input data, this final surface model to returns a far better representation of the actual depth to water below the ground surface throughout the southeast.

As SERIC has also collated an extensive database of Plantation Forestry across the region we were able to overlay gross plantation boundaries on the Depth to Water Table surface to assist delineation of water table depth below forested areas.

The outputs of SERIC's study have proven invaluable in assisting recent discussions between the forestry industry, DWLBC, and the SENRMB and in relation to water allocation planning issues.

SERIC's new Depth to Water dataset overlain with gross plantation forestry boundaries to assist the assesment of water recharge rates under forested land.

In an environment of reduced rainfall and increasing need to manage the region’s most important natural asset, it’s groundwater, DWLBC enlisted SERIC to assist in the production models which would more reflect the depth of the water table below the ground surface more accurately than had previously been the case. The driver for this was the need to account for the impact of all groundwater impacting activities, so that Water Allocation Plans developed by the South East Natural Resources Management Board (SENRMB) could take into account not just extraction of groundwater, but variations in recharge to the unconfined or upper aquifer. The construction of the Depth to Water models and resultant Depth to Water Table surface have provided valuable data in forwarding the discussions between DWLBC, SENRMB and forestry during consultation on the Water Allocation Plan for the Lower Limestone Coast. The addition of DEM data has further fine tuned the model.