Although all reasonable care has been taken in the preparation of the information contained in this document, the Chief Executive of the Department of Agriculture and Food and its officers and the State of Western Australia accept no responsibility for any errors or omissions it may contain, whether caused whether in negligence or otherwise, or for any loss howsoever caused, resulting from reliance on, or the use or disclosure of, this information or any part thereof. Staff from the Department of Agriculture and Food (Noel Wilson, Lorraine Hartle, Gae Plunckett, Tara Slaven, Francis Bright, Terry Hill, Anella Conrades, Peter Gardiner, Mark Pridham and Noel Schoknecht) are thanked for help with logistics and management. The authors acknowledge the assistance of the other members of DAFWA's Weaber Plain project team: Adam Lillicrap, Grant Stainer, Russell Speed, Henry Smolinski, Jim Dixon, and Justin Laycock.
Construction of the M2 feeder canal linking ORIA and Weaber Plain and the final period of irrigation planning, environmental management and associated approval processes began later in 2009. As part of the environmental planning and approval process, the WA Government was required to produce an underground water management plan water and hydrodynamic plan. As a result, the Western Australian Department of Agriculture and Food (DAFWA) was asked to lead an investigative program to support the second phase of the modelling.
Of the issues related to groundwater, uncertainty existed about the location, hydraulic properties and yield of the palaeochannel aquifer and permeability in the northern area of the proposed development, where the aquifer was expected to be absent (Lawrie et al. 2010). After the mid-1990s, a rise in groundwater levels was also observed in areas remote from the influence of the ORIA (Border Creek, Eastern Weaber Plain, Knox and Keep Plains).
Introduction
This report describes the results of the drilling and monitoring conducted to complete Phase 1, which addresses Holes 1-4. RMTR 370: Surface water characteristics of the Weaber Plain and Lower Keep River catchments (Bennett & George 2011) – addresses Phase 5 and Intervals 9-10.
Background
Rainfall
There are two different seasons; the 'wet' monsoon period from November to April when 90 percent of the annual rainfall falls, and the 'dry' from May to October. Ivanhoe Station data is reported as it is closest to the Weaber Plain (36 km west) and has the longest continuous record. A marked increase in annual rainfall at Ivanhoe Station was observed after 1993 and is represented by plots of the 10-year rolling average and cumulative annual residual rainfall (Figure 2).
Bedrock geology
Physiography
The Weaber Plain is located within the 1032 km2 Border Creek catchment, which is a sub-catchment of the 5082 km2 Keep River catchment (GHD 2010). There are no incised channels across the Weaber Plain, except towards the north-east where Border Creek becomes more defined as it heads east towards the Keep River. Additionally, overflow from the ORIA (D8 drain outlet) and surrounding hills flows northeast to Border Creek.
The mean annual flow of the Keep River at the Legune Road crossing, just upstream of its confluence with Border Creek, is approximately 430 GL and varies between 16 and 1613 GL in response to wet season rainfall (Bennett & George 2011). Analyzes of the daily flow of Border Creek and the Keep River indicate that the flow from Border Creek averages only 10 percent of the flow of the Keep River. These gauge data show that, per unit area, the Border Creek catchment is much less responsive to rainfall than the Keep River catchment and contributes a relatively small volume of surface water flow to the Keep River (Bennett & George 2011).
There is no groundwater flow in Border Creek and it contains no significant permanent pools (Bennett & George 2011). However, the Keep River contains a series of four pools, three dominated by tidal influences (K1 to K3) and one by river processes only (K4).
Methods
- Drill site selection
- Drilling methods
- Drill samples
- Bore construction and development
- Groundwater sampling and level monitoring
- Groundwater level analysis
- Access and surveying
The monitoring bores are made with a diameter of 50 mm; class 18 threaded PVC sheath or 100mm diameter, class 12 PVC sheath. Screens for the monitoring bores were of the same material as the blank housing and were perforated by machined horizontal slots, a 0.5 mm housing opening with a 50 mm diameter and a 1.0 mm housing opening with a diameter of 100mm. The annulus of all sounding bores is filled with 2-4 mm fine sand to a minimum of 1 m above the top of the shielded part.
Production nozzles were constructed with 200 mm diameter, grade 12 PVC liner and JohnsonTM wire-wrapped stainless steel screens with a 1 mm opening. Monitoring and production holes were developed using lift and/or air lift until the discharge water was clear and free of sand, with flow rates taken at regular intervals. Initial groundwater levels in all new monitoring and production holes were taken no more than one week after hole construction and again after completion of the drilling program.
Survey North also surveyed the top of casing (TOC) and concrete pad (ground level) of all newly completed wells using a Trimble® R6 GPS system that provides 30mm vertical and 20mm horizontal accuracy. All wells were surveyed using the 1994 Australian Geocentric Datum, Zone 52, and all elevations are referenced to the Australian Altitude Datum (AHD).
Results and discussion
- Aquifer conceptualisation and groundwater recharge
- Location and aquifer characteristics of the palaeochannel
- Location and characteristics of sediments at Border Creek
- Location and characteristics of sediments in the southern Weaber Plain
- Groundwater heads
In areas north of Border Creek, the shallower water table (8 m BGL) was attributed to the sandy nature of the surface soils in the area. This rise probably reflects the depth to the water table and the high permeability of the aquifer in the area. Evidence indicates that significant land reclamation of the Weaber Plain occurred from 1993 to 1994 and that this reclamation is responsible for much of the water table rise.
Distribution of groundwater salinity and determination of the chloride mass balance of the recharge, implying that a one-dimensional recharge model dominates the Weaber Plain away from the influence of the ORIA. An updated interpretation of the paleochannel extent and alluvial sequence in the Border Creek area, derived from the recent drilling, is shown in Figure 7. The hydraulic properties of the paleochannel were determined from each production bore and some piezometers and is reported in Paul et al..
In summary, the hydraulic conductivity and transmissivity of paleochannel sands and gravels do not change. Border Creek has a catchment area of over 1,032 km2 and extends approximately 30 km northwest of the Weaber Plain farmland development. An interpretation of the location of permeable sediments within this area is shown in Figure 7.
In the area south of Weaber Plain Road, alluvial flood sequences occur at the base of the Pincombe Range. It lies at the eastern end of the paleochannel, interpreted by O'Boy et al. 2001) and in the middle of the paleochannel interpreted by Lawrie et al. At the western edge of Weaber Plain (Plots 8 and 8A), there is a strong east-west groundwater gradient from the mound below Lot 3.
The image also shows an elevated groundwater table to the northwest originating from Border Creek and a groundwater sink northeast of Brown Ridge at the junction of Weaber, Knox, and Keep Plains. The water table geometry confirms that there is an interaction between the ORIA and the western Weaber Plain governed by transmissivity and gradient. However, downstream, east, and north of Brown Ridge, the regolith and steep hydraulic gradient of the aquifer indicate limited interconnection between this area and the Border Creek aquifer (Lots north of Brown Ridge) and the eastern Weaber Plain.
Conclusion
Smolinski, H, Laycock, J & Dixon, J 2011, Soil assessment of the agricultural lands of the Weaber Plain, Resource Management Technical Report 369, Department of Agriculture and Food, Western Australia. Org: KIM Bore name: 10WP31 Project: Ord Supervisors: R George & B Paul Date Catchment: Keep River Sub-basin: Weaber Plain – Border Creek Site: Weaber Plain Proposed Farmlands – West Side Lot 18. Org: KIM Bore name: 10WP32 Project: Ord Supervisor(s): B Paul Date Watershed: Keep River Sub-Watershed: Weaber Plain – Border Creek Location: Weaber Plain Proposed Farmlands – West Side Lot 18.
Simons Date Catchment: Keep River Catchment: Weaber Plain - Border Creek Location: Weaber Plain, on the boundary between proposed lots 5 and 18. George Date Catchment: Keep River Sub-catchments: Weaber Plain - Border Creek Location: Weaber Plain Proposed Agricultural Land - West Side Lot 3. Simons Date Catchment: Keep River Sub-catchment: Weaber Plain - Border Creek Location: Weaber Plain, on the boundary between proposed lots 2 and 3.
Simons Date Catchment: Hou River Sub-catchment: Weaber Plain – Border Creek Location: Weaber Plain, on boundary between proposed Sites 3 and 6. George Date Catchment: Hou River Sub-catchment: Weaber Plain – Border Creek Location: Weaber Plain Proposed Agricultural Lands – West side Lot 3. 12/07/2010 Catchment: Hou River Sub-catchment: Weaber Plain – Border Creek Location: Weaber Plain Proposed Farmland – West side Lot 3. Land Use: Pastoral Pasture Year Cleared: Uncleared.
Raper Date Catchment: Hou River Sub-catchment: Weaber Plain – Border Creek Location: – Weaber Plain Proposed Farmlands – north of Brown Ridge, northern boundary of Lot 9. Raper Date Catchment: Hou River Sub-catchment: Weaber Plain – Border Creek Location : Weaber Plain Proposed Farmlands – north of Brown Ridge, on Lot 9B. Rapist Date Catchment: Hou River Sub-catchment: Weaber Plain – Border Creek Location: Weaber Plain Proposed Farmlands – north of Brown Ridge.
Raper Date Watershed: Keep River Sub-Watershed: Weaber Plain - Border Creek Location: Weaber Plain Proposed Agricultural Areas - North of Brown Ridge, northern boundary of Lot 9B. Smith Date Watershed: Keep River Sub-Watershed: Weaber Plain – Border Creek Location: Weaber Plain, northern boundary of proposed lot 9B. Simons Date Watershed: Keep River Sub-Watershed: Weaber Plain – Border Creek Location: Weaber Plain, on the southern boundary of the proposed lot 21B.
Simons Date Catchment: Keep River Sub-catchment: Weaber Plain – Border Creek Location: Weaber Plain Proposed Agricultural Lands – South East Boundary of Lot 20. Smith Date Catchment: Keep River Sub-catchment: Weaber Plain – Border Creek Location: Weaber Plain, north of proposed Lot 9B. The influence of ORIA on groundwater levels in the western Weaber Plain has been inferred by Laws (1987) and documented by Lawrie et al.
The long-term recharge rates on the Weaber Plain are two orders of magnitude greater than those reported by Tickell et al.
