Author(S)Peter Hekmeijer, Hanna Zydorand Mark Reid

CMI Number:102920

Author(s)Peter Hekmeijer, Hanna Zydorand Mark Reid

Department of Primary Industries

Future Farming Systems Research Division,

Epsom, Victoria, Australia

© The State of Victoria, 2011

Disclaimer

This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.

Acknowledgments

This project would not be possible without the support and cooperation of the following:

Landholders:

Iven, Iris and Marcia Field (Mirranatwa);

Rob Lawrance and Georgie Luckock (Gatum);

Harry Youngman (Grassdale, Digby);

George Buttas (Tee Tree Creek, Elaine);

Forestry companies: Adrian Marti, Elders Forestry;

Pat McEwen Consulting for Macquarie Forestry;

Neil Harris, AKD Softwoods;

Kevin Johnson, Midway;

Universities:

La TrobeUniversity:Dr. John Webb, Fahmida Perveen, Josh Dean and Michael Reynolds;

University of Melbourne: Dr. Tom Baker, John Collopy;

University of Ballarat:Dr. Peter Dahlhaus, Bob Smith;

Industry:

Campbells Scientific

HydroTerra

Portland Water Supply Engineers

Theiss Services

Executive Summary

The rapid expansion of cropping and blue gum plantations has been a part of a substantial landuse change in south-western Victoria. With increasing development and predicted drier climate conditions, the competition for water in the region is intense and may come under stricter regulatory control. The modelling carried out in this geologically diverse region presently uses generalised input data because the catchment scale data on the land use impacts on hydrology is currently poor and inadequate. This project will provide valuable new knowledge about impacts of major land uses to inform sustainable land management and protection of natural resources in this region.

To determine the relationships between any particular land use and groundwater and surface water, as well as improve confidence in prediction of impacts of land use, detailed information is needed at a sub-catchment or catchment scale. In order to achieve that, water and salt entering and leaving a catchment, including groundwater and the salt that it carries, must be measured and water and salt balances developed.

The project has adopted a paired catchment approach which is a well established comparative technique to measure hydrologic parameters of competing land uses. At each site, at least two sub-catchments with different agricultural land uses (grazing, some cropping, and tree plantations) but the same or very similar topography, geology and soils were instrumented. The size of sub-catchments ranges from approx. 50ha (Mirranatwa) to 500ha (Digby). All sub-catchments comply with the criteria established for this method.

Four paired research sites have been established. Three are located near Hamilton, namely at Digby, Gatum and Mirranatwa, and the fourth is located in the Morrisons-Sheoak area, near Ballarat. They comprise groundwater observation bores (some existing and some new), stream gauges and rainfall stations. Data collected at each site (e.g. stream flow and EC, groundwater levels and EC in bores, rainfall) will be used to construct water and salt balances, which will allow accurate quantification and comparison of the catchment scale impacts of these agricultural land uses on surface water, groundwater and salinity.

This report describes the drilling and weir construction programs, together with borehole results for the new and existing groundwater monitoring bores. Altogether, 37 new monitoring bores were constructed at the three paired research sites in the Hamilton area and a total of nine gauged weirs were established at all four paired research sites. There are 31 pre-existing monitoring bores shared mainly between the Gatum and Mirranatwa farm sites and the Morrisons-Sheoak paired sites.

Groundwater level and salinity data from the bore networks,together with flow and salinity data from the weir sites, will be used to perform analyses to assess the impacts of different land uses on groundwater levels, groundwater quality, groundwater flow, groundwater-stream interaction, and stream flow and quality.

Contents

Introduction

Research sites

Drilling program

Drilling results

Weir establishment

Data Loggers and Telemetry

Recommendations

References

Appendix A: Completion reports and logs of new bores

Appendix B: Weir designs

Tables

Table 1 Calculated area of paired research sites.

Table 2 Land use and geology of paired research sites

Table 3 Monitoring bores in paired sub-catchments

Table 4. Bore construction details and groundwater levels

Figures

Figure 1. Map of south-western Victoria showing the locations of the four paired sub-catchment study sites.

Figure 2. Geological map of the Mirranatwa farm (M1-south) and plantation (M2-north) sites showing stream gauges and bore sites.

Figure 3. Geological map of Morrisons-Sheoak farm (MS1-west) and plantation (MS2-east) sites showing stream gauges and bore sites.

Figure 4. Geological map of the Gatum farm (G1-west) and plantation (G2-east) sites showing stream gauges and bore sites.

Figure 5. Geological map of the Digby farm site showing stream gauges (D1a and D1b) and bore sites.

Figure 6. Geological map of the Digby plantation site (D3) showing stream gauges and bore sites.

Figure 7. Map of the Digby farm and plantation sites showing location of the geological cross-section (see Figure 8).

Figure 8. North-South geological cross-section through the Digby farm and plantation sites (see Figure 5 and 6).

Figure 9. The V-notch weir at the Digby plantation site.

Introduction

This report describes the establishment of surface water and groundwater monitoring sites in south west Victoria as part of FFSR Project 102920 "Catchment scale water and salinity impacts of changing land use in south western Victoria" (short title: "Catchment scale impacts of land use in south western Victoria"). This report is aligned to the 2009-10 Annual Report (Reid et al 2010) from which some of the introductory text herein is taken.

This project forms part of the DPI Key Project, “Accountable Agriculture” (FF104), which aims to equip farmers with new knowledge and smart decision making tools to balance production and environmental outcomes more efficiently and effectively. Project 102920 addresses policy issues relating to impacts of tree plantations on water security (Action 2.20 in the Victorian Water White Paper) and sustainable management of plantations (Victorian Timber Strategy). La TrobeUniversity is a key collaborative partner. The Universities of Melbourne and Ballarat are also collaborative partners.

The rationale for this project includes (i) substantial land use change (increase in blue gum plantations in particular) and uncertainty about its impacts or sustainability, (ii) the lack of high quality catchment-scale hydrologic data (particularly including groundwater data), and (iii) the inadequacy of plot-scale data for extrapolation to catchment scale hydrologic budgets. To address these issues, four (4) paired catchment research sites have been established in geologically different landscapes to calculate and compare water and salt balances.

The water and salt balances will be used to accurately quantify and compare the catchment scale impacts of these agricultural land uses on surface water, groundwater and salinity. The new data and knowledge gained will also improve the prediction capacity of regional process models such as CAT.

At each site location, two sub-catchments with different agricultural land uses (grazing-dominant versus tree plantations) but sharing the same or very similar topography, geology and soils were identified to establish automated monitoring networks to measure the amount of water and salt entering the sub-catchments (as rainfall and groundwater) and leaving the site (as surface water and groundwater). The salt storage in each sub-catchment will be measured, both above and below the watertable.

All four paired research sites possess automated monitoring networks comprising groundwater observation bores, stream gauges and rainfall stations, and there is now a program in place to also establish evaporation pans. At this stage, the three priority research sites are those established in the Hamilton area (i.e. Mirranatwa, Gatum and Digby). They have the advantages of: (i) more manageable size for effective data collection, (ii) better monitoring control, and (iii) proximity to each other. In contrast, the Morrisons-Sheoak paired site, near Ballarat, is isolated, quite large, and lacks groundwater observation control. There is presently insufficient budget to address the shortfall in groundwater data at this site.

Project objectives

•To install a monitoring system to measure the water and salt balance in four paired catchments with different geological settings and land use, (particularly plantation forestry against grazing)

•To use the collected data to construct water and salt balances for the catchments and accurately quantify and compare the catchment scale impacts of the different agricultural land uses on the surface water and groundwater resources and salinity.

•To use the above new data and conceptual models of catchment processes developed at each paired research site to validate and strengthen the current predictive catchment models such as CAT.

Research sites

The project has adopted a paired catchment approach, which is a well established comparative technique to measure hydrologic parameters of competing or different land uses. For each pair of research sites, criteria for selection were as follows:

• each pair should be located in an area of significant interest to stakeholders in regards to water security, agricultural or environmental issues (including salinity);
• each pair should comprise one with predominantly grazing/cropping and one with predominantly tree plantations;
• each individual site should encompass a defined surface drainage area of reasonable size (i.e. approx. 50 ha to 1000 ha);
• each pair should be of similar or comparable size and located reasonably close together (i.e. within 10 km, preferably closer);
• each pair should share the same or very similar geology, soil, landscape and climate characteristics;
• the downstream end of each site should satisfy requirements for weir construction, including complete capture of surface flow leaving the site and negligible alteration to flow from the site;
• prior existence of monitoring bores was considered in the selection of all but the Digby paired site.

The following 4 locations were selected for establishment of paired sub-catchment research sites in south western Victoria(Figure 1, Tables 1 and 2):

• Mirranatwa - VictoriaValley, southern Grampians, Glenelg Hopkins CMA region (Figure2);
• Morrisons-Sheoak - near Meredith, eastern MooraboolRiver catchment, Corangamite CMA region (Figure 3);
• Gatum - Eastern Dundas Tablelands, Glenelg Hopkins CMA region (Figure 4);
• Digby - upper CrawfordRiver catchment, Glenelg Hopkins CMA region (Figures 5 and 6)

Each research site location comprises a pair of sub-catchments, one of each pair supporting wood plantations (blue gum or pine) and the otherpredominantly or completely supporting grazing. In the case of the Digby site, the monitoredgrazing area is comprised of two adjoined sub-catchments to make the monitored area more comparable in size to the monitored blue gum plantation area.

The 4 paired sites cover a range of topography, soils and geology (Table 2) but each pair has been selected on the basis of same or similar physical dimensions. The catchment boundaries have been constructed based on the 1:100,000 topographic layer which has a 20 m contour interval. More accurate topographic and boundary delineation than currently exists is required for accurate water balance calculation. This will soon be addressed as part of a surveying program that will also include levelling of all the monitoring stations.

The Gatum plantation site has trees of approximately five years age, the Mirranatwa plantation site approximately three years, and the Digby plantation site has a mixture of immature and mature tree plantations up to about 12 years of age. The Morrisons-Sheoak pine plantation site is a mixture of mature and immature trees.

Figure 1. Map of south-western Victoria showing the locations of the four paired sub-catchment study sites.

Table 1 Calculated area of paired research sites.

Table 2 Land use and geology of paired research sites

Drilling program

A drilling program (Table 3 and Figures 2, 3, 4, 5 and 6) was planned and undertaken to obtain geological data and to establish or enhance bore networks on the three Hamilton paired sites. Together with the existing bores, these will provide effective groundwater monitoring control across each of these sites.

Within the constraints of the project resources, it was important to ensure that bores were positioned at the head and bottom of each catchment and that reasonable bore coverage was attained longitudinally and transversely with respect to catchment drainage direction. It was endeavoured to arrange bores, as much as accessibility allowed, into lines or transects to aid geological model construction and hydrogeological analysis and interpretation.

The purpose ofthe drilling is essentially twofold:

• to obtain lithological samples for geological and hydrogeological interpretation, and chemical analysis; and
• to construct observation bores to measure groundwater levels, electrical conductivity, chemistry, and aquifer parameters, the latter via slug tests.

A total of 37 new monitoring bores were completed from June 2009 to February 2010 (Table 3) of which 12 shallow bores (up to 15 m total depth) were drilled using a truck mounted auger whilst 25 deeper bores (up to approximately 30 m total depth) were drilled using an air hammer or mud rotary technique.

Groundwater level and salinity data from the bore networks will be used to perform analyses to assess the impacts of different land uses on groundwater levels, groundwater quality, groundwater flow and groundwater-stream interaction.

Appendix A contains the geological logs and bore construction details. For each bore, unless otherwise stated, there is a gravel pack and screenlocated near the bottom of the casing string with a 1m length of sump to collect any fine materialthat may enter the screen and settle out. Some bores were screened in two positions due to hydrogeological characteristics of the geological strata. For example, a bore drilled to total depth with little indication of reasonable groundwater flow at total deptha second screen has been installed higher up the bore, at a position that suggests measurable groundwater flow.

Within the budget constraints, drilling priorities were confined to the three pairs of sites around the Hamilton and Grampians area. It is hoped that, with assistance from University of Ballarat, more bores will eventually be installed at the Morrisons-Sheoak paired sites (MS1 and MS2) , particularly on the farm site (MS1), to add to the existing bores owned by them,.

Air hammer was the preferred drilling technique and this was applied at the majority of drilling sites. It is an efficient technique that allows collection of accurate, contaminant-free cutting samples for geological interpretation and chemical analysis. Unfortunately, unexpectedly difficult, unstable drilling conditions were encountered in the Digby area necessitating the application of the mud rotary technique. Although an efficient technique able to counteract the difficult conditions, it was more expensive and resulted in less accurate samples with some contamination. Due to its greater expense, it also meant that less bores were drilled at the Digby sites than originally planned (four bore sites were not drilled).

Each new bore was constructed to internationally recognised standards for groundwater monitoring using 50 mm diameter Class 9 PVC (Poly Vinyl Chloride) casing and slotted PVC screen with a fine (2mm) gravel pack. The gravel pack is placed around the screen and bentonite pellets are placed above the gravel pack to prevent annular leakage of groundwater from the developed interval. The remaining annulus is then backfilled with clay cuttings from the drilled hole. Each bore has been fitted with a robust 1 m high steel collar, whichis cemented in at the surface. The collar serves several purposes including protection, security, and providing space to seat data loggers.

Further bores are desirable, particularly at the Digby and Morrisons-Sheoak sites, although there is presently insufficient budget to support this. Nonetheless, except for Morrisons-Sheoak, the current bore coverage is regarded as adequate and should allow a reasonably concise interpretation of geology and groundwater configuration (Figures 2, 3, 4, 5, 6).

Drilling results

The new bores listed in Table 3 add to bores already existing at several sites, including Morrisons-Sheoak (drilled by University of Ballarat), Mirranatwa (drilled by DPI) and Gatum (drilled by DPI). Each new bore has a geological log.

Figures 2 to 6 show the bore networks and new weir locations at each of the four pairs of research sites (i.e. Mirranatwa, Morrisons-Sheoak, Gatum and Digby).