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Reductions in water use following rehabilitation of a flood-irrigated area on the Murray River in South Australia
Agricultural Water Management 96 (2009) 1679–1682
Contents lists available at ScienceDirect
Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat
Short communication
Reductions in water use following rehabilitation of a flood-irrigated area on the Murray River in South Australia L.M. Mosley a,*, N. Fleming b a b
Water Quality Branch, South Australian Environment Protection Authority, GPO Box 2607, Adelaide, SA 5001, Australia South Australian Research Development Institute, GPO Box 397, Adelaide, SA 5001, Australia
A R T I C L E I N F O
A B S T R A C T
Article history: Received 17 October 2008 Accepted 3 June 2009 Available online 9 July 2009
Water use was monitored during rehabilitation of flood-irrigated farms in the lower Murray River of South Australia. Ten irrigation offtakes at six farms were monitored over a period of two years during the rehabilitation process. Full rehabilitation consisted of improved inlet structures, flow metering, elimination of water leaks, laser levelling of paddocks, and construction of re-use systems to recycle excess surface irrigation runoff. Partial rehabilitation consisted of the same improvements with the exception of the re-use system. The mean water use per watering of 0.61 0.08 Ml/ha for the fully rehabilitated farm was approximately one third of that for non-rehabilitated farms (1.89 0.15 Ml/ha) and two thirds of that for partially rehabilitated farms (0.99 0.07 Ml/ha). These differences were statistically significant at the 95% confidence level. A large improvement in efficiency of water use was achieved by upgraded water delivery infrastructure and laser levelling of paddocks. Considerable improvement in water use efficiency was also gained, however, only by installation of re-use systems. It is expected that the overall rehabilitation of irrigation infrastructure will result in a significant reduction of water extracted from the river for flood irrigation in this region. Further longer term monitoring is required to confirm this. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Flood-irrigated pasture Dairy farming Infrastructure improvement Water use efficiency Runoff recycling
1. Introduction Flood irrigation is used throughout the world for irrigation of pasture and crops such as rice and cotton. Flood irrigation is typically less efficient than other forms of irrigation such as sprinklers and drippers (Wood and Finger, 2006). However, in many Australian locations flood irrigation is the preferred method because of benefits in reducing salinisation of heavy clay soils. Flood irrigation also has relatively low capital, labour, maintenance and energy costs. Dairy farming has the highest water consumption for agricultural production in Australia, estimated at 5902 Gl per year, or 39.5% of all irrigated water (National Land and Resources Audit, 2002). There are approximately 5200 ha of flood-irrigated dairy farms on the former floodplain of the Murray River in South Australia between the townships of Mannum and Wellington, known collectively as the Lower Murray Reclaimed Irrigation Area (LMRIA). Most of this land was drained and developed for agriculture between 1880 and 1940 with levee banks constructed along the river’s edge to control flooding. Since completion of the barrages to prevent seawater intrusion at the mouth of the river in
* Corresponding author. Tel.: +61 8 8139 9900; fax: +61 8 8139 9901. E-mail address: [email protected] (L.M. Mosley). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.06.001
the 1940s, the LMRIA ground surface has been 1.0–1.5 m below the river level. Dairy farming is the predominant land use in this region with a smaller area used for beef cattle, hay production and lifestyle farming. The saline groundwater table below these floodplains is close to the paddock surface and can reach the soil surface through upward groundwater pressure and capillary action (DWLBC, 2003). This, coupled with the ability to gravity feed water as the floodplain is now lower than the river, has meant flood irrigation is the preferred method of irrigation in the LMRIA. Historically, some of the irrigation practices in the LMRIA have been inefficient due to poor condition of the water delivery infrastructure, lack of water metering, non-level paddocks, and, in some instances, poor management practices resulting in excess surface irrigation runoff. As a result large volumes of drainage water containing pollutants such as nutrients and pathogens have been pumped back to the river (EPA, 2008). This discharge is considered to pose a risk to the aquatic ecosystem of the river, recreational users, and drinking water supplies for townships and the city of Adelaide (EPA, 2001). Improving the efficient use of water and reducing pollutant loads to the river are important for the future of the dairy industry in the Lower Murray. The current prolonged drought on the River Murray has substantially reduced surface water availability with many irrigators currently on very restricted allocations (0–30%). Across Australia, reduced irrigation water availability has increased pressure on the dairy industry
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L.M. Mosley, N. Fleming / Agricultural Water Management 96 (2009) 1679–1682
to use water more efficiently (Armstrong, 2004; Bethune and Armstrong, 2004). Based on community concerns about poor river water quality, the Australian Federal and South Australian State governments have funded (A$ 22 million) and implemented, in cooperation with irrigators, a major rehabilitation program of the LMRIA. The overall objective was to reduce pollutant loads returned to the river. Irrigators received funding (up to A$ 3130/ha government funding) and also contributed their own funding (A$ 470/ha mandatory contribution plus any additional funding needed to complete the works). Approximately 4200 ha of land was rehabilitated, and the remaining approximately 1000 ha retired from commercial farming. It was considered that the key to achieving the program objective was to reduce drainage water volumes. Various infrastructure improvements have been undertaken including new water delivery infrastructure (siphons/sluices, meters, inlet channels), water metering, laser grading of paddock surfaces, and construction of runoff re-use systems (>50 kl/ha capacity) to recycle excess surface irrigation runoff water and pollutants that
were previously returned to the river (EPA, 2005). Water meters and runoff recycling systems were the mandatory components of these works. This paper reports the results of a two-year monitoring study of irrigation water use after the rehabilitation project was undertaken. The aim was to determine what reductions in water use occurred and what contributed to these reductions. 2. Methods Six irrigation areas were selected for the study: Cowirra, Baseby, Wall Flat, Pompoota, Woods Point, and Jervois (Fig. 1). These are six of the twenty four individual irrigation areas that comprise the LMRIA on the Murray River between the townships of Mannum and Wellington. Monitoring stations were established at ten irrigation water offtakes of the study areas. Fig. 2 shows a schematic cross-section of a typical (rehabilitated) irrigation area in the LMRIA. The water offtakes consist of polyethylene sluices and siphons (600 mm pipe diameter) and extend through a clay
Fig. 1. Study locations (dark circles) and townships (open circles) on the Lower Murray River in South Australia.
L.M. Mosley, N. Fleming / Agricultural Water Management 96 (2009) 1679–1682
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Fig. 2. Schematic cross-section of a typical irrigated area in the LMRIA (not to scale).
levee bank. During irrigation, gates or valves are opened to allow water to be gravity fed from the river into an inlet channel, and then through an outlet into the irrigation bay. Bays are the individual paddock watering unit and are typically 400 m long by 25–50 m wide and are laser levelled at a 1:500 to 1:800 gradient. Prior to full rehabilitation, ‘salt’ drains (2 m deep) at the end of the bay returned excess surface irrigation runoff and saline groundwater to the river. After rehabilitation, all surface runoff water is collected (prior to the salt drain) in shallow (1 m deep) re-use/‘toe’ drains and recycled back on farm via pumping. Water flows were measured by installing ultrasonic flow meters in the sluices or siphons. The meters were independently calibrated approximately every three months for the two-year duration of the study. Flow data was downloaded and processed at this time. Irrigators recorded the date and location of their irrigations to enable calculation of water use per hectare. All the study locations were active dairy farms. The typical summer
irrigation season in the LMRIA is from September to April with occasional irrigations during the winter if conditions are dry. 3. Results and discussion Flood-irrigation water volumes measured at the different study areas are shown in Table 1. The stage of rehabilitation for each study location is also shown. The mean water use per watering of 0.61 0.08 Ml/ha for the fully rehabilitated sites at Woods Point was approximately one third of the mean water use per watering (1.89 0.15 Ml/ha) for the non-rehabilitated sites, and two thirds of that at the partly rehabilitated sites (0.99 0.07 Ml/ha). The difference between the means was statistically significant at the 95% confidence level (Table 1). Further longer term monitoring at more fully rehabilitated sites is required to confirm these findings. However the results for the fully rehabilitated sites compare well to previous data (EPA, 2005)
Table 1 Irrigation water use at the study locations in comparison with their stage of rehabilitation. Site
Cowirra 1 2 3
Baseby 4 Wall Flat 5 Pompoota 6 Woods Pt 7 8 Jervois 9 10
All All All a
Year
na
Total water use (Ml)
Mean water use per irrigation 95% CI (Ml/ha)
Rehabilitation stageb
2005 2006 2005 2006 2005 2006
7 3 21 9 7 7
62.7 30.0 219.1 88.4 117.7 127.0
1.57 0.22 1.75 0.29 1.21 0.16 1.13 0.18 1.31 0.37 0.90 0.22
Non Non Partly Partly Partly Partly
2005 2006
8 3
382.2 78.0
1.83 0.35 1.00 0.12
Non Non
2005 2006
7 4
60.7 38.3
0.58 0.20 0.64 0.12
Partly Partly
2005 2006
17 18
190.6 115.9
1.91 0.25 0.84 0.14
Non Partly
2005 2006 2005 2006
20 7 4 6
457.1 106.86 96.9 97.5
0.99 0.04 0.55 0.12 0.85 0.14 0.68 0.04
Partly Fully Partly Fully
2005 2006 2005 2006
2 6 4 8
45.1 123.5 116.1 191.5
1.58 0.37 2.09 0.14 3.06 1.04 1.90 0.18
Non Non Non Non
1.89 0.15c 0.99 0.07c 0.61 0.08c
Non Part Full
2005–2006 2005–2006 2005–2006
58 97 13
n is the number of waterings measured at each location. Non-rehabilitated: original infrastructure; Partly rehabilitated: new inlet channels, meter, laser levelled; Fully rehabilitated: new inlet channels, meter, laser levelled, reuse system. c The 95% confidence intervals were non: 1.73–2.04, part: 0.92–1.06, full: 0.52–0.69. As these confidence intervals do not overlap the differences are statistically significant. b
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L.M. Mosley, N. Fleming / Agricultural Water Management 96 (2009) 1679–1682
for a trial site at Cowirra (average of 0.7 Ml/ha). The partly rehabilitated (new inlet channels, laser levelled) and nonrehabilitated areas were also comparable to previous findings in the LMRIA (Murray and Philcox, 1995; Fleming et al., 2003) and other locations (Wood and Finger, 2006). The site at Pompoota clearly illustrated the effect of partial rehabilitation as water use decreased from 1.8 Ml/ha to 0.8 Ml/ha during the study duration (Table 1). The site at Wall Flat appeared comparably more efficient than other partly rehabilitated sites. This farm had a much shorter irrigation bay length than the other sites that likely resulted in quicker and more efficient irrigation events. The improvements in efficiency of water use following full or partial rehabilitation in the LMRIA are attributed to a combination of improved inlet structures (new sluices and channels), water metering, elimination of leaks, laser levelling of paddocks, and construction of re-use systems to recycle excess surface irrigation runoff. A large proportion of the reduction in water use was achieved by new water delivery infrastructure, metering and laser levelling, but additional efficiency gains were achieved following construction of re-use systems (Table 1). Laser levelling results in a smoothly sloping surface that delivers water quickly and efficiently along the irrigation bay (Philcox, 2002). This substantially reduces both the amount of irrigation water required and the volume of sub-surface drainage. Rehabilitation has also reduced watering times and consolidated watering infrastructure, producing time savings for the irrigator. There was some unexplained variability within the results at several sites (Table 1). For example, site 4 at Baseby and site 10 at Jervois showed efficiency gains which were not clearly linked to rehabilitation, and even at the same study location some monitoring sites increased water use between 2005 and 2006 (e.g. Cowirra 1) while some decreased (e.g. Cowirra 2 and 3). We analysed rainfall data to see if efficiency gains at some sites could be a result of variable crop irrigation water requirements. The total annual rainfall at Murray Bridge for 2005 and 2006 was 491 mm and 241 mm respectively. In theory the drier year experienced in 2006 should have increased crop irrigation water requirements but may also have lead to increased incentives for irrigators to achieve improved water efficiency through different management strategies (e.g. watering short to conserve water). As only two sites were fully rehabilitated, further longer term monitoring is required to confirm the wider applicability of these findings. Nevertheless these preliminary results strongly indicate that the overall LMRIA rehabilitation project should produce large reductions in the amount of water extracted from the river. The current water allocation plan for the LMRIA allows for a total irrigation allocation of 89.5 Gl per year, equating to an irrigation water allocation of 13.92 Ml/ha per year, plus an additional allocation of 3–6.5 Ml/ha per year for control of land salinisation. This allocation is variable, depending on the average rainfall at a particular irrigation area (RMCWMB, 2004). Based on a predicted post-rehabilitation application rate of less than 0.7 Ml/ha per watering, the current irrigation allocation would allow for about 20 irrigation waterings per annum. Approximately 16–18 irrigations per annum are required for laser levelled paddocks and 12 for nonlasered paddocks, with average intervals between irrigations of 14 and 18 days, respectively (Philcox, 2002). This indicates there should be sufficient water available for irrigators to maintain full production under the allocation (which is now metered). The current drought and low flows on the Murray River have resulted in irrigators receiving only a portion of their allocation (60% in 2006–2007). Irrigators who have completed rehabilitation works and are more water efficient will be best equipped to maximise their production during drought.
A detailed cost:benefit analysis of the LMRIA rehabilitation project has not been undertaken. However, based on the predicted water savings (50 Gl) and market cost of water (approximately A$ 1200 per Ml at time of study) versus the total project cost (A$ 25 million), the estimated benefit:cost ratio is between 2 and 3 (EPA, 2008). There was no apparent negative impact on farm production noted from the rehabilitation works during the timescale of the monitoring project. Further long term monitoring is required to verify this, particularly in relation to possible salt build-up due to increased runoff recycling. 4. Conclusion Water use per hectare was monitored from ten different irrigation offtakes on farms with differing degrees of rehabilitation. The average water use per watering of 0.61 Ml/ha for the fully rehabilitated sites was one third of the average water use per watering (1.89 Ml/ha) for non-rehabilitated sites. A large proportion of the reduction in water use was achieved by upgraded water delivery infrastructure and laser levelling of paddocks, but significant additional gains in efficiency were achieved following construction of runoff re-use systems. The rehabilitation project is expected to result in large total water savings across the floodirrigated areas in the lower Murray River. Further longer term monitoring of fully rehabilitated sites is required to confirm these findings. Acknowledgements The receipt of National Action Plan (NAP) for Water Quality and Salinity funding to undertake this monitoring study is gratefully acknowledged. Thanks are also due to irrigators who were involved in the study and the staff of Water Data Services Pty Ltd. for providing technical support with monitoring. The assistance of Ying He with map production is also acknowledged. The valuable comments of two anonymous reviewers are gratefully acknowledged. References Armstrong, D.P., 2004. Water use efficiency and profitability on an irrigated dairy farm in northern Victoria: a case study. Aust. J. Exp. Agric. 44, 137–144. Bethune, M.G., Armstrong, D.P., 2004. Overview of the irrigated dairy industry in Australia. Aust. J. Exp. Agric. 44, 127–130. DWLBC, 2003. Regional salt and water balances for the Lower Murray in South Australia. Report 2003/27. Department of Water Land and Biodiversity Conservation, Adelaide, South Australia. EPA, 2001. Ambient Water Quality Monitoring of the Murray River 1990–1999. Environment Protection Authority, Adelaide, South Australia. EPA, 2005. Cowirra Surface Irrigation Re-use Trial. Environment Protection Authority, Adelaide, South Australia. EPA, 2008. Lower Murray Reclaimed Irrigation Area Environmental Monitoring Report, Phase 1. Environment Protection Authority, Adelaide, South Australia. Fleming, N.K., Gepp, M.J., Cox, J.C., Hutson, J.L., 2003. Reduced Nutrient Loads to the Lower Murray in South Australia, Milestone Report No. 7-watering volumes and runoff 2001/3. South Australian Research and Development Institute, Adelaide, South Australia. Murray, P., Philcox, M.B., 1995. An assessment of irrigation runoff from flood irrigated dairy pastures of the Lower Murray, Primary Industries and Resources South Australia report. Adelaide, South Australia. National Land and Resources Audit, 2002. Australians and Natural Resource Management. Australian Natural Resources Atlas V2.0. Commonwealth of Australia. Philcox, M.B., 2002. Laser Levelling on the Lower Murray: a collection of articles and papers on laser levelling from research undertaken on the reclaimed swamps. Primary Industries and Resources South Australia report. Adelaide, South Australia. RMCWMB, 2004. Water Allocation Plan for the Murray River Prescribed Watercourse. River Murray Catchment Water Management Board, South Australia. Wood, M.L., Finger, L., 2006. Influence of irrigation method on water use and production of perennial pastures in northern Victoria. Aust. J. Exp. Agric. 46, 1605–1614.
Contents lists available at ScienceDirect
Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat
Short communication
Reductions in water use following rehabilitation of a flood-irrigated area on the Murray River in South Australia L.M. Mosley a,*, N. Fleming b a b
Water Quality Branch, South Australian Environment Protection Authority, GPO Box 2607, Adelaide, SA 5001, Australia South Australian Research Development Institute, GPO Box 397, Adelaide, SA 5001, Australia
A R T I C L E I N F O
A B S T R A C T
Article history: Received 17 October 2008 Accepted 3 June 2009 Available online 9 July 2009
Water use was monitored during rehabilitation of flood-irrigated farms in the lower Murray River of South Australia. Ten irrigation offtakes at six farms were monitored over a period of two years during the rehabilitation process. Full rehabilitation consisted of improved inlet structures, flow metering, elimination of water leaks, laser levelling of paddocks, and construction of re-use systems to recycle excess surface irrigation runoff. Partial rehabilitation consisted of the same improvements with the exception of the re-use system. The mean water use per watering of 0.61 0.08 Ml/ha for the fully rehabilitated farm was approximately one third of that for non-rehabilitated farms (1.89 0.15 Ml/ha) and two thirds of that for partially rehabilitated farms (0.99 0.07 Ml/ha). These differences were statistically significant at the 95% confidence level. A large improvement in efficiency of water use was achieved by upgraded water delivery infrastructure and laser levelling of paddocks. Considerable improvement in water use efficiency was also gained, however, only by installation of re-use systems. It is expected that the overall rehabilitation of irrigation infrastructure will result in a significant reduction of water extracted from the river for flood irrigation in this region. Further longer term monitoring is required to confirm this. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Flood-irrigated pasture Dairy farming Infrastructure improvement Water use efficiency Runoff recycling
1. Introduction Flood irrigation is used throughout the world for irrigation of pasture and crops such as rice and cotton. Flood irrigation is typically less efficient than other forms of irrigation such as sprinklers and drippers (Wood and Finger, 2006). However, in many Australian locations flood irrigation is the preferred method because of benefits in reducing salinisation of heavy clay soils. Flood irrigation also has relatively low capital, labour, maintenance and energy costs. Dairy farming has the highest water consumption for agricultural production in Australia, estimated at 5902 Gl per year, or 39.5% of all irrigated water (National Land and Resources Audit, 2002). There are approximately 5200 ha of flood-irrigated dairy farms on the former floodplain of the Murray River in South Australia between the townships of Mannum and Wellington, known collectively as the Lower Murray Reclaimed Irrigation Area (LMRIA). Most of this land was drained and developed for agriculture between 1880 and 1940 with levee banks constructed along the river’s edge to control flooding. Since completion of the barrages to prevent seawater intrusion at the mouth of the river in
* Corresponding author. Tel.: +61 8 8139 9900; fax: +61 8 8139 9901. E-mail address: [email protected] (L.M. Mosley). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.06.001
the 1940s, the LMRIA ground surface has been 1.0–1.5 m below the river level. Dairy farming is the predominant land use in this region with a smaller area used for beef cattle, hay production and lifestyle farming. The saline groundwater table below these floodplains is close to the paddock surface and can reach the soil surface through upward groundwater pressure and capillary action (DWLBC, 2003). This, coupled with the ability to gravity feed water as the floodplain is now lower than the river, has meant flood irrigation is the preferred method of irrigation in the LMRIA. Historically, some of the irrigation practices in the LMRIA have been inefficient due to poor condition of the water delivery infrastructure, lack of water metering, non-level paddocks, and, in some instances, poor management practices resulting in excess surface irrigation runoff. As a result large volumes of drainage water containing pollutants such as nutrients and pathogens have been pumped back to the river (EPA, 2008). This discharge is considered to pose a risk to the aquatic ecosystem of the river, recreational users, and drinking water supplies for townships and the city of Adelaide (EPA, 2001). Improving the efficient use of water and reducing pollutant loads to the river are important for the future of the dairy industry in the Lower Murray. The current prolonged drought on the River Murray has substantially reduced surface water availability with many irrigators currently on very restricted allocations (0–30%). Across Australia, reduced irrigation water availability has increased pressure on the dairy industry
1680
L.M. Mosley, N. Fleming / Agricultural Water Management 96 (2009) 1679–1682
to use water more efficiently (Armstrong, 2004; Bethune and Armstrong, 2004). Based on community concerns about poor river water quality, the Australian Federal and South Australian State governments have funded (A$ 22 million) and implemented, in cooperation with irrigators, a major rehabilitation program of the LMRIA. The overall objective was to reduce pollutant loads returned to the river. Irrigators received funding (up to A$ 3130/ha government funding) and also contributed their own funding (A$ 470/ha mandatory contribution plus any additional funding needed to complete the works). Approximately 4200 ha of land was rehabilitated, and the remaining approximately 1000 ha retired from commercial farming. It was considered that the key to achieving the program objective was to reduce drainage water volumes. Various infrastructure improvements have been undertaken including new water delivery infrastructure (siphons/sluices, meters, inlet channels), water metering, laser grading of paddock surfaces, and construction of runoff re-use systems (>50 kl/ha capacity) to recycle excess surface irrigation runoff water and pollutants that
were previously returned to the river (EPA, 2005). Water meters and runoff recycling systems were the mandatory components of these works. This paper reports the results of a two-year monitoring study of irrigation water use after the rehabilitation project was undertaken. The aim was to determine what reductions in water use occurred and what contributed to these reductions. 2. Methods Six irrigation areas were selected for the study: Cowirra, Baseby, Wall Flat, Pompoota, Woods Point, and Jervois (Fig. 1). These are six of the twenty four individual irrigation areas that comprise the LMRIA on the Murray River between the townships of Mannum and Wellington. Monitoring stations were established at ten irrigation water offtakes of the study areas. Fig. 2 shows a schematic cross-section of a typical (rehabilitated) irrigation area in the LMRIA. The water offtakes consist of polyethylene sluices and siphons (600 mm pipe diameter) and extend through a clay
Fig. 1. Study locations (dark circles) and townships (open circles) on the Lower Murray River in South Australia.
L.M. Mosley, N. Fleming / Agricultural Water Management 96 (2009) 1679–1682
1681
Fig. 2. Schematic cross-section of a typical irrigated area in the LMRIA (not to scale).
levee bank. During irrigation, gates or valves are opened to allow water to be gravity fed from the river into an inlet channel, and then through an outlet into the irrigation bay. Bays are the individual paddock watering unit and are typically 400 m long by 25–50 m wide and are laser levelled at a 1:500 to 1:800 gradient. Prior to full rehabilitation, ‘salt’ drains (2 m deep) at the end of the bay returned excess surface irrigation runoff and saline groundwater to the river. After rehabilitation, all surface runoff water is collected (prior to the salt drain) in shallow (1 m deep) re-use/‘toe’ drains and recycled back on farm via pumping. Water flows were measured by installing ultrasonic flow meters in the sluices or siphons. The meters were independently calibrated approximately every three months for the two-year duration of the study. Flow data was downloaded and processed at this time. Irrigators recorded the date and location of their irrigations to enable calculation of water use per hectare. All the study locations were active dairy farms. The typical summer
irrigation season in the LMRIA is from September to April with occasional irrigations during the winter if conditions are dry. 3. Results and discussion Flood-irrigation water volumes measured at the different study areas are shown in Table 1. The stage of rehabilitation for each study location is also shown. The mean water use per watering of 0.61 0.08 Ml/ha for the fully rehabilitated sites at Woods Point was approximately one third of the mean water use per watering (1.89 0.15 Ml/ha) for the non-rehabilitated sites, and two thirds of that at the partly rehabilitated sites (0.99 0.07 Ml/ha). The difference between the means was statistically significant at the 95% confidence level (Table 1). Further longer term monitoring at more fully rehabilitated sites is required to confirm these findings. However the results for the fully rehabilitated sites compare well to previous data (EPA, 2005)
Table 1 Irrigation water use at the study locations in comparison with their stage of rehabilitation. Site
Cowirra 1 2 3
Baseby 4 Wall Flat 5 Pompoota 6 Woods Pt 7 8 Jervois 9 10
All All All a
Year
na
Total water use (Ml)
Mean water use per irrigation 95% CI (Ml/ha)
Rehabilitation stageb
2005 2006 2005 2006 2005 2006
7 3 21 9 7 7
62.7 30.0 219.1 88.4 117.7 127.0
1.57 0.22 1.75 0.29 1.21 0.16 1.13 0.18 1.31 0.37 0.90 0.22
Non Non Partly Partly Partly Partly
2005 2006
8 3
382.2 78.0
1.83 0.35 1.00 0.12
Non Non
2005 2006
7 4
60.7 38.3
0.58 0.20 0.64 0.12
Partly Partly
2005 2006
17 18
190.6 115.9
1.91 0.25 0.84 0.14
Non Partly
2005 2006 2005 2006
20 7 4 6
457.1 106.86 96.9 97.5
0.99 0.04 0.55 0.12 0.85 0.14 0.68 0.04
Partly Fully Partly Fully
2005 2006 2005 2006
2 6 4 8
45.1 123.5 116.1 191.5
1.58 0.37 2.09 0.14 3.06 1.04 1.90 0.18
Non Non Non Non
1.89 0.15c 0.99 0.07c 0.61 0.08c
Non Part Full
2005–2006 2005–2006 2005–2006
58 97 13
n is the number of waterings measured at each location. Non-rehabilitated: original infrastructure; Partly rehabilitated: new inlet channels, meter, laser levelled; Fully rehabilitated: new inlet channels, meter, laser levelled, reuse system. c The 95% confidence intervals were non: 1.73–2.04, part: 0.92–1.06, full: 0.52–0.69. As these confidence intervals do not overlap the differences are statistically significant. b
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L.M. Mosley, N. Fleming / Agricultural Water Management 96 (2009) 1679–1682
for a trial site at Cowirra (average of 0.7 Ml/ha). The partly rehabilitated (new inlet channels, laser levelled) and nonrehabilitated areas were also comparable to previous findings in the LMRIA (Murray and Philcox, 1995; Fleming et al., 2003) and other locations (Wood and Finger, 2006). The site at Pompoota clearly illustrated the effect of partial rehabilitation as water use decreased from 1.8 Ml/ha to 0.8 Ml/ha during the study duration (Table 1). The site at Wall Flat appeared comparably more efficient than other partly rehabilitated sites. This farm had a much shorter irrigation bay length than the other sites that likely resulted in quicker and more efficient irrigation events. The improvements in efficiency of water use following full or partial rehabilitation in the LMRIA are attributed to a combination of improved inlet structures (new sluices and channels), water metering, elimination of leaks, laser levelling of paddocks, and construction of re-use systems to recycle excess surface irrigation runoff. A large proportion of the reduction in water use was achieved by new water delivery infrastructure, metering and laser levelling, but additional efficiency gains were achieved following construction of re-use systems (Table 1). Laser levelling results in a smoothly sloping surface that delivers water quickly and efficiently along the irrigation bay (Philcox, 2002). This substantially reduces both the amount of irrigation water required and the volume of sub-surface drainage. Rehabilitation has also reduced watering times and consolidated watering infrastructure, producing time savings for the irrigator. There was some unexplained variability within the results at several sites (Table 1). For example, site 4 at Baseby and site 10 at Jervois showed efficiency gains which were not clearly linked to rehabilitation, and even at the same study location some monitoring sites increased water use between 2005 and 2006 (e.g. Cowirra 1) while some decreased (e.g. Cowirra 2 and 3). We analysed rainfall data to see if efficiency gains at some sites could be a result of variable crop irrigation water requirements. The total annual rainfall at Murray Bridge for 2005 and 2006 was 491 mm and 241 mm respectively. In theory the drier year experienced in 2006 should have increased crop irrigation water requirements but may also have lead to increased incentives for irrigators to achieve improved water efficiency through different management strategies (e.g. watering short to conserve water). As only two sites were fully rehabilitated, further longer term monitoring is required to confirm the wider applicability of these findings. Nevertheless these preliminary results strongly indicate that the overall LMRIA rehabilitation project should produce large reductions in the amount of water extracted from the river. The current water allocation plan for the LMRIA allows for a total irrigation allocation of 89.5 Gl per year, equating to an irrigation water allocation of 13.92 Ml/ha per year, plus an additional allocation of 3–6.5 Ml/ha per year for control of land salinisation. This allocation is variable, depending on the average rainfall at a particular irrigation area (RMCWMB, 2004). Based on a predicted post-rehabilitation application rate of less than 0.7 Ml/ha per watering, the current irrigation allocation would allow for about 20 irrigation waterings per annum. Approximately 16–18 irrigations per annum are required for laser levelled paddocks and 12 for nonlasered paddocks, with average intervals between irrigations of 14 and 18 days, respectively (Philcox, 2002). This indicates there should be sufficient water available for irrigators to maintain full production under the allocation (which is now metered). The current drought and low flows on the Murray River have resulted in irrigators receiving only a portion of their allocation (60% in 2006–2007). Irrigators who have completed rehabilitation works and are more water efficient will be best equipped to maximise their production during drought.
A detailed cost:benefit analysis of the LMRIA rehabilitation project has not been undertaken. However, based on the predicted water savings (50 Gl) and market cost of water (approximately A$ 1200 per Ml at time of study) versus the total project cost (A$ 25 million), the estimated benefit:cost ratio is between 2 and 3 (EPA, 2008). There was no apparent negative impact on farm production noted from the rehabilitation works during the timescale of the monitoring project. Further long term monitoring is required to verify this, particularly in relation to possible salt build-up due to increased runoff recycling. 4. Conclusion Water use per hectare was monitored from ten different irrigation offtakes on farms with differing degrees of rehabilitation. The average water use per watering of 0.61 Ml/ha for the fully rehabilitated sites was one third of the average water use per watering (1.89 Ml/ha) for non-rehabilitated sites. A large proportion of the reduction in water use was achieved by upgraded water delivery infrastructure and laser levelling of paddocks, but significant additional gains in efficiency were achieved following construction of runoff re-use systems. The rehabilitation project is expected to result in large total water savings across the floodirrigated areas in the lower Murray River. Further longer term monitoring of fully rehabilitated sites is required to confirm these findings. Acknowledgements The receipt of National Action Plan (NAP) for Water Quality and Salinity funding to undertake this monitoring study is gratefully acknowledged. Thanks are also due to irrigators who were involved in the study and the staff of Water Data Services Pty Ltd. for providing technical support with monitoring. The assistance of Ying He with map production is also acknowledged. The valuable comments of two anonymous reviewers are gratefully acknowledged. References Armstrong, D.P., 2004. Water use efficiency and profitability on an irrigated dairy farm in northern Victoria: a case study. Aust. J. Exp. Agric. 44, 137–144. Bethune, M.G., Armstrong, D.P., 2004. Overview of the irrigated dairy industry in Australia. Aust. J. Exp. Agric. 44, 127–130. DWLBC, 2003. Regional salt and water balances for the Lower Murray in South Australia. Report 2003/27. Department of Water Land and Biodiversity Conservation, Adelaide, South Australia. EPA, 2001. Ambient Water Quality Monitoring of the Murray River 1990–1999. Environment Protection Authority, Adelaide, South Australia. EPA, 2005. Cowirra Surface Irrigation Re-use Trial. Environment Protection Authority, Adelaide, South Australia. EPA, 2008. Lower Murray Reclaimed Irrigation Area Environmental Monitoring Report, Phase 1. Environment Protection Authority, Adelaide, South Australia. Fleming, N.K., Gepp, M.J., Cox, J.C., Hutson, J.L., 2003. Reduced Nutrient Loads to the Lower Murray in South Australia, Milestone Report No. 7-watering volumes and runoff 2001/3. South Australian Research and Development Institute, Adelaide, South Australia. Murray, P., Philcox, M.B., 1995. An assessment of irrigation runoff from flood irrigated dairy pastures of the Lower Murray, Primary Industries and Resources South Australia report. Adelaide, South Australia. National Land and Resources Audit, 2002. Australians and Natural Resource Management. Australian Natural Resources Atlas V2.0. Commonwealth of Australia. Philcox, M.B., 2002. Laser Levelling on the Lower Murray: a collection of articles and papers on laser levelling from research undertaken on the reclaimed swamps. Primary Industries and Resources South Australia report. Adelaide, South Australia. RMCWMB, 2004. Water Allocation Plan for the Murray River Prescribed Watercourse. River Murray Catchment Water Management Board, South Australia. Wood, M.L., Finger, L., 2006. Influence of irrigation method on water use and production of perennial pastures in northern Victoria. Aust. J. Exp. Agric. 46, 1605–1614.