Science, Technology and Engineering

Environmental Geoscience

Research Programs

Groundwater

Dryland salinity is one of the most important problems facing Australian agriculture today, as salinisation reduces the productivity of large areas of farmland. Developing management strategies relies on a complete knowledge of the processes that are causing the salinisation; although these are understood at a general level, they vary greatly at a local (paddock) scale.

The Environmental Geoscience group at La Trobe University has been studying dryland salinisation in western and central Victoria for over 8 years, in conjunction with the Glenelg-Hopkins and Wimmera Catchment Management Authorities, Primary Industries Research Victoria (Bendigo) and local landcare groups. The Australian Institute for Nuclear Science and Energy has provided funding for groundwater dating.

Our work has focussed on two aspects: groundwater chemical and isotopic studies, and the effects of landuse (vegetation) and climate on groundwater levels, through very detailed studies of individual sites and medium-long term modelling. There are 3 current and 2 completed PhD projects on these topics, along with 2 MSc and 15 Honours projects, and additional PhD projects are offered. The results have appeared in a number of publications and have been presented at numerous international conferences.

Chemical and isotopic studies

We use chemical and isotopic techniques to determine how groundwater flows through the aquifers and what is causing groundwater to come to the surface in particular locations and develop areas of salinisation. The results of these studies have been used to help manage the groundwater resources of the region.

Our studies demonstrate that soil processes, particularly plant uptake and interactions with clays, quickly change the chemical composition of infiltrating rain water to that of dilute seawater. Salinisation is predominantly due to evaporation where groundwater lies close to the surface, even if the groundwater at depth is fresh. Evaporation may cause salt to build up in low permeability clay-rich soils, but does not necessarily lead to salinisation if the salt lies below the pasture root zone, so productive farmland is frequently underlain by salty soils and saline groundwater.

On the basalt plains of western and central Victoria we have shown that many saline scalds and lakes are related to the geology: edges of basalt lava flows, and upwards groundwater flow from the buried river valley sediments beneath. Recharge to the groundwater in the basalts and underlying sediments occurs mostly through the volcanoes; the thick clayey soils of the plains allow only small amounts of saline recharge. However, the addition of this saline soil water causes the groundwater to progressively increase in salinity down the flow path. Overall, recharge is determined largely by soil texture rather than vegetation cover.

Effects of landuse (vegetation) and climate on groundwater levels

A very detailed study of a farm paddock using data loggers to record hourly groundwater fluctuations showed that drainage lines carrying water only intermittently act as the main recharge area. The drainage line also has very saline soils and groundwater because the watertable is shallow and there is insufficient flow to flush the salt. Thus replanting vegetation along ephemeral drainage lines will intercept runoff and reduce recharge and salinisation.

Tree plantations are believed to reduce recharge to groundwater, but preliminary detailed studies on a plantation, again using data loggers, have shown that there is little difference to nearby farmland. Preferential recharge may be occurring during heavy rainfall events down the tree roots.

Hydrological modelling using a monthly time-step has been carried out on a number of lakes in western and central Victoria, to determine the controls on lake level and salinity. This has shown that groundwater is rarely a significant component of the lake budget, and that saline baseflow is more important than evaporation in increasing salinity in water supply reservoirs. Climatic fluctuations are the primary factor in lake water and salt budgets, although land use changes have an impact in some instances. The models allow prediction of future trends under any likely climatic scenario.

This modelling has been extended to watertables in the basalt plains of western Victoria, by relating infiltration (from local climate data) to watertable fluctuations. Initial progress is promising, and the model is presently being refined by determining the best measure of infiltration and the time lag between infiltration events and watertable response. The results will then be tested against existing catchment models like CAT (Catchment Area Tool) and MIKE SHE, to see how different management strategies (tree planting, level of water usage) will impact on groundwater levels.

Refereed journal papers

Raiber, M., Webb, J.A and Bennetts, D., in review. Strontium isotopes as tracers to delineate aquifer interactions and groundwater salinisation in the basalt plains of southeastern Australia. Journal of Hydrology,

Edwards, M.D. and Webb, J.A., in review. Influence of soil processes on groundwater composition, southeastern Australia. Hydrogeology Journal,

Raiber, M. and Webb, J.A., 2008. Development of the Streatham Deep Lead System in Western Victoria: Implications for Tertiary tectonism and landscape evolution. Australian Journal of Earth Sciences, 55, 493-508.

Bennetts, D.A., Webb, J.A., McCaskill, M. and Zollinger, R., 2007. Dryland salinity processes within the discharge zone of a local groundwater system, Southeastern Australia. Hydrogeology Journal, 15, 1197-1210.

Tweed, S.O., Leblanc, M., Webb, J.A. and Lubczynski, M.W., 2006. Remote sensing and GIS for mapping groundwater recharge and discharge areas in salinity prone catchments, southeast Australia. Hydrogeology Journal 15, 75-96.

Bennetts, D.A., Webb, J.A., Stone, D.J.M. and Hill, D.M., 2006. Understanding the salinisation process for groundwater in an area of southeastern Australia, using hydrochemical and isotopic evidence. Journal of Hydrology, 323, 178-192.

Papers in conference proceedings

Yihdego, Y. and Webb, J. A., 2008. Modelling of seasonal and longterm trends in lake salinity in Southwestern Victoria, Australia. Proceedings of Water Down Under April 2008, 994-1000.

Hagerty, S. and Webb, J.A., 2008. Aquifer interactions and groundwater discharge into streams identified using 87Sr/86Sr isotope ratios in the Upper Loddon Catchment, Central Victoria. Proceedings of Water Down Under April 2008, 1272-1278.

Raiber, M., Webb, J.A., Jacobsen, G.E., Chisari R. and Williams, A.A., 2008. Geological controls on the spatial variability of groundwater recharge and salinity in a regional-scale basalt aquifer in western Victoria. Proceedings of Water Down Under April 2008, 1279-1283.

Webb, J.A., Williams, B.G., Bailue, K., Walker, J. and Anderson, J.W., 2008. Short-term groundwater dynamics at a paddock scale. Proceedings of Water Down Under April 2008, 1493-1500.

Raiber, M., Webb, J.A., Jacobsen, G., Chisari, R. and Neklapilova, B., 2007. Aquifer interactions and their impact on groundwater resources in the basalt plains of Western Victoria. Twelfth International Symposium on Water-Rock Interaction, Kunming, China, August 2007; Conference Proceedings, 985-988.

Bennetts, D.A. and Webb, J.A., 2004. Processes affecting groundwater quality in a basalt aquifer system in southern Australia. In: R.B. Wanty and R.R. Seal (Editors), Proceedings 11th International Symposium on Water-Rock Interaction, Saratoga Springs, USA, 347-351. Balkema, Rotterdam.

Edwards, M.D. and Webb, J.A. 2003. Ground-truthing of a Tempest airborne electromagnetic survey in the salinised Kamarooka catchment, near Bendigo in central Victoria. In Roach, I.C. (ed.), Advances in regolith; Proceedings CRC LEME Regional Regolith Symposium, Adelaide, Nov 2003, 110-114.

Bennetts, D.A., Webb J.A. and Gray C.M., 2003. Distribution of Plio-Pleistocene basalts and regolith around Hamilton, western Victoria, and their relationship to groundwater recharge and discharge. In Roach, I.C. (ed.), Advances in regolith; Proceedings CRC LEME Regional Regolith Symposium, Adelaide, Nov 2003, 11-15.

PhD Theses

Matthias Raiber, in progress. Quantification of future changes in groundwater salinisation in the Basalt Plains of the Eastern Glenelg Hopkins CMA, using hydrogeological, chemical and isotopic techniques. PhD thesis, La Trobe University.

Sarah Hagerty, in progress. Groundwater resources and salinity associated with granites in the upper Wimmera, western Victoria. PhD thesis, La Trobe University.

Yohannes Yihdego, in progress. Modeling hydrograph response to climate and land use changes and relating the impacts to groundwater salinisation and lake level/salinity in western Victoria

Matthew Edwards, 2007. Dryland salinity of Mt William Creek, upper Wimmera catchment; a hydrological, hydrogeological and hydrogeochemical study. PhD thesis, La Trobe University

Darren Bennetts, 2006. Hydrology, hydrogeology and hydrogeochemistry of groundwater flow systems within the Hamilton basalt plains, western Victoria, and their role in dryland salinisation. PhD thesis, La Trobe University.

Msc Theses

Jane McLeish, in progress. Quantifying groundwater discharge into rivers systems using radon-222 as a tracer.

Martin Fussell, in progress. Surface water - groundwater interactions along the Murrumbidgee River around Narrandera, NSW (joint project with Environmental Management, Wodonga).

Honours Theses

Sharon Honicke, in progress. Hydrogeology and hydrogeochemistry of the upper Campaspe deep lead.

John Sharples, in progress. Modelling management effects on Lake Bolac, Fiery Creek and Salt Creek - evaluation of the Catchment Analysis Tool (CAT).

Dale McKenzie, in progress. Groundwater - surface water interactions in the Cairn Curran catchment.

Kate Bailue, 2007. Groundwater recharge and flow on a small scale (paddock) in the Willaura area, western Victoria.

Catherine Hart, 2007. Salinisation and groundwater - surface water interactions in the Glenelg River, western Victoria.

Matt Ryan, 2007. Using water and salt budgets to quantify the effect of blue-gum plantations on water sources in the Eastern Dundas Tableland, western Victoria.

Katherine Coady, 2007. Hydrogeochemical study of Upper Bet Bet catchment.

Sarah Hagerty, 2006. Groundwater - surface water interactions in the Tullaroop catchment, central Victoria.

Meredith Bormann, 2004. Variation in rainfall composition across Victoria.

Michael Ernest, 2004. Hydrogeology around Lake Bolac, Western Victoria.

Janaya Wattie, 2003. Salinity of the Hopkins River, western Victoria.

Ben Beatty, 2003. Hydrogeology and water chemistry of the groundwater in the upper Loddon catchment, Clunes-Creswick district.

Chihiro Tanaka, 2003. Hydrogeology and water chemistry of groundwater in the Campaspe valley.

Matthew Edwards, 2002. Chemical, isotopic and geophysical study of dryland salinity at Kamarooka, central Victoria.

Darren Bennetts, 2001. Locating preferential flowpaths within the Willaura catchment using isotopic geochemistry.