Ord
Water overview
Significant water events
There were two relatively high magnitude flood events in the region during the 2013–14 year. Both these events are highlighted in Figure W1.
On 18 January 2014, daily flow in the lower Ord River peaked above 1,800 m3/s, greater than a 1 in 4 year flood event (Department of Water 2013). This event was attributed to a large amount of rainfall occurring across the region during 15–16 January. At Kununurra airport, more than 120 mm was recorded during the 48-hour period. According to the Bureau of Meteorology's Design rainfall website, this is equivalent to a greater than 1 in 2 year rainfall event.
On 8 February 2014, daily flow in the lower Ord River was above 3,840 m3/s, equivalent to a 1 in 27–35 year flood event (Department of Water 2013). This event was attributed to a very large amount of rainfall occurring across the lower part of the Ord region. During 6–8 February 2014, more than 365 mm of rainfall was observed at the Kununurra airport during the 72-hour period. According to the Bureau of Meteorology's Design rainfall website, this is equivalent to a greater than 1 in 50 year rainfall event. Lake Argyle filled to 122% capacity (12,730,000 ML) as a result of this rainfall event and remained above 100% for the remainder of the 2013–14 year.
Figure W1 Flood events in the lower Ord River during the 2013–14 year
Both of these rainfall-runoff events contributed to the above average monthly flows in the region during January–February (see Streamflow section below) as well as meeting requirements outlined in the environmental water provisions for the lower Ord River (see Environmental benefit note).
Soil moisture
Figure W2 shows that soil moisture was generally above average in the Ord region during the 2013–14 year (compared with the 1970–2014 period). The soil moisture is based on a simple conceptual representation of soil water storage and transfer processes averaged over a 5 km x 5 km grid cell derived from the Australian Water Resources Assessment system landscape model (AWRA-L) version 3.0. The model produces a soil moisture grid for the region at a daily time step, which is then averaged over the entire year to produce an annual soil moisture grid. The annual grid represents the mean daily volume of soil moisture across the region during the year.
Figure W2 Annual soil moisture deciles for the Ord region during the 2013–14 year
The combination of above average rainfall and soil moisture conditions across the Ord region has contributed to the above average streamflow in the upper reaches of the Ord River during the 2013–14 year (see Streamflow).
Streamflow
The upper Ord and Negri rivers contribute most of the inflows to Lake Argyle. The location of these rivers is provided in Figure P7 in the 'Contextual information'.
Total annual flows in these rivers during the 2013–14 year were approximately 50% above the mean annual flow, and approximately four times that recorded during the 2012–13 year. The 3-month period between January and March is usually when the majority of the total annual flow occurs in these rivers. Total flow during this period was well above the long-term average (figures W3–W4), particularly during January–February, which contributed to the overall above average annual flow during the 2013–14 year.
Interestingly, total flow during February in these rivers upstream of Lake Argyle (figures W3–W4) was still less than expected given the total rainfall during this month was well above the 90th percentile (see Climate overview). This is likely to be because the majority of rainfall during the storm event on 6–8 February 2014 (see Significant water events), which made up more than half the total February rainfall, was concentrated in the lower part of the Ord region.
Figure W3 Total monthly flow along upper Ord River during the 2013–14 year compared with the long-term average and percentiles for the river
Figure W4 Total monthly flow along Negri River during the 2013–14 year compared with the long-term average and percentiles for the river
Streamflow in the lower Ord River below Lake Argyle is measured at Tarrara Bar (Station 809339). The location of this station is provided in Figure P7 in the 'Contextual information'.
Total annual flow during the 2013–14 year in the lower Ord River was equivalent to the mean annual flow; however, for the majority of the year monthly flow was below the long-term average (Figure W5). Flow was only relatively large during the early part of the wet season (January–February), which contributed to the overall average annual flow during the year. During these two months, flow was above the 90% percentile. Flow during February was the highest on record.
The record high flow during February in the lower Ord River can be attributed to a combination of high runoff from the unregulated catchment area during the large rainfall event on 6–8 February 2014 (see Significant water events), which was concentrated in the lower part of the Ord region, and overflow from Lake Argyle. Given Lake Argyle was almost 100% capacity by the end of January, much of the runoff generated in the upper catchments during February will have overflowed from Lake Argyle into the downstream river.
The flow conditions in the Ord region, both upstream and downstream of Lake Argyle, reflect the rainfall observed throughout the region during the 2013–14 year, (see Climate overview), particularly during the early part of the wet season (January–February).
Figure W5 Total monthly flow along lower Ord River during the 2013–14 year compared with the long-term average and percentiles for the river
Major water initiatives
Ord–East Kimberley Expansion Project
The Ord–East Kimberley Expansion Project is a major initiative of the Western Australian Government. The State committed $220 million from the Royalties for Regions fund under the Ord Irrigation Expansion Project and a further $195 million was contributed by the Australian Government via the East Kimberley Development Package.
The first stage of the expansion will develop 74 km² of irrigated farmland known as the Goomig farmlands (Figure W6). Construction of the irrigation infrastructure commenced in 2010 and was still in development throughout the 2013–14 year. In late 2013 the Western Australian Government signed an agreement with Kimberley Agricultural Investment (KAI) for the company to develop the 74 km² of Goomig farmlands with an option to develop a further 60 km² of the Knox Plain (Figure W6) over the next few years. KAI propose to develop these areas to establish a sugar industry in the region.
Figure W6 Proposed expansion in the Ord River Irrigation Area
The Ord Irrigation Cooperative currently holds a licence for diversion of 335,000 ML/year from the Ord River for the Ivanhoe and Packsaddle irrigation districts (see Water entitlements and other statutory water rights). Additional water demand from the Ord River to support irrigation development in the Goomig farmlands and the Knox Plain is expected to be 80,000–170,000 ML/year and 60,000–110,000 ML/year respectively.
There are proposals to develop other irrigated areas in the Ord region, such as the Ord West Bank and the Mantinea areas, the Carlton and Keep River plains and areas alongside the Packsaddle Plain (Figure W6). Development of these areas could take place in the next 5–10 years. Further details on these potential irrigation areas are given in Chapter 3 of the Ord Surface Water Allocation Plan.
Further information on the Ord–East Kimberley Expansion Project can be found at the following Government of Western Australia websites: