Ord
Water access and use

This note provides information about the water access rights granted by jurisdictions to the users of the region's water resources and the associated allocation announcements and abstractions.

The 2014 Account acknowledges that the legislative water resource management frameworks relating to Australian water rights vary greatly across jurisdictions, sometimes making comparisons difficult. To facilitate meaningful comparisons between the 2014 water accounting reports, the Bureau of Meteorology has developed and applied an accounting concept to classify and report water entitlements within a water asset/water liability framework.

According to that framework, water rights for the Ord region for the 2013–14 year have been classified as shown below.

In the Ord region, surface water allocations were equal to 100% of the water access entitlement.

The volumes of surface water allocation and abstraction for the 2013–14 year, compared to the previous two years, are shown in Figure 1. The percentage shows the ratio of abstraction to the allocation announcement.

Figure 1 Surface water allocations and abstractions in the Ord region for the years ending 30 June 2014, 2013 and 2012

Figure 1 shows that the allocation announcements for surface water diversion during the 2013–14 year were the same as the previous two years for urban water and irrigation scheme supply and only marginally less for individual users.

Surface water abstractions to the Ord River Irrigation Area during the 2013–14 year decreased slightly compared to the previous two years, which may be attributed to the increased rainfall during the year (see Climate overview). Abstractions to the urban water system marginally increased during the year compared to the previous two years; abstractions for individual users were similar to the previous year.

In the Ord region, groundwater allocations were equal to 100% of the water access entitlement.

The volumes of groundwater water allocation and abstraction for the 2013–14 year, compared to the previous two years, are shown in Figure 2. The percentage shows the ratio of abstraction to the allocation announcement.

Figure 2 Groundwater allocations and abstractions in the Ord region for the years ending 30 June 2014, 2013 and 2012

Figure 2 shows that the allocation announcements for groundwater extraction during the 2013–14 year remained relatively unchanged from  the previous two years.

Groundwater extractions during the 2013–14 year for both individual users and the urban water system were also relatively unchanged from the 2012–13 year. Figure 2 shows extractions to individual users during the 2011–12 year were almost 100% of the allocation; however, this was because metered abstraction data were unavailable for one of the large mining licences that year. Consequently, it was assumed that abstraction was equal to the annual announcement.

There were no water restrictions in the Ord region during the 2013–14 year.

Water entitlement trades and transfers in the Ord region can occur within the same surface water management area (see the Trades and water rights transfers section in the 'Contextual information'); however, no trades or transfers of surface water or groundwater licence entitlements occurred during the 2013–14 year.

More information on water entitlement transactions can be found on the Western Australian Department of Water website.

Water is released from Lake Argyle for hydroelectric generation. The power station requires enough water released to enable at least 210 gigawatt hours/year to be generated (see the Operating rules and constraints section in the 'Contextual information'). To generate this power commitment, about 2,100,000 ML/year must be released from Lake Argyle. The water released has the dual purpose of administering water access entitlements downstream, including bulk irrigation in the Ord River Irrigation Area, and other agricultural, commercial, industrial, and mining activities.

For a summary of the water volumes allocated for various economic purposes within the Ord region, including the actual volumes abstracted, refer to Surface water rights and Groundwater rights above.

Water provided for the environment to maintain specific levels in the lower Ord River has the dual purpose of satisfying ecological requirements and allowing access to boats for recreational purposes.

Periods of low flow in the lower Ord River are administered to support traditional hunting and fishing activities (see the Cultural water management section in the 'Contextual information'). This occurs from time to time when maintenance and inspection work on dam infrastructure is required. During the 2013–14 year, the hydroelectric power station had a shutdown between 21–26 March 2014. Consequently, flow in the lower Ord River was reduced during this period (see Figure 4 in the 'Environmental benefit' note).

Introduction

Water for environmental benefit in the Ord region is provided according to the following environmental water management scenario:

• planned, partly regulated surface water.

Environmental water legislation

Environmental water provisions in the Ord region are defined for the lower Ord River (downstream of Lake Argyle). These provisions are outlined in the Ord Surface Water Allocation Plan.

The plan outlines a flow regime required to maintain current ecological conditions in the lower Ord River, including:

• populations of fish and macro invertebrates
• vegetation community structure
• water quality
• channel morphology.

The plan recognises that different parts of the flow regime, such as low, high and overbank flows have different ecological functions. The different components of the flow regime, which reflect the seasonality of the river, are important to the ecology of the lower Ord River.

Environmental water provisions

Environmental water provisions for the lower Ord River comprise three components:

1. baseflow (minimum flow rate)
2. wet season flood events
3. infrequent (high magnitude) wet season flood events.

All three components of the flow regime are critical for maintaining ecological conditions in the Ord River. The required flow regimes are maintained from a combination of water releases from Lake Argyle and Lake Kununurra, and unregulated catchment inflow.

The Water Corporation of Western Australia operates the two storages and manages the releases of water. The Department of Water monitors the flow along the lower Ord River at the Tarrara Bar gauging station (Station 809339—see Figure P7 in the 'Contextual information' for location) to ensure the required flow is being maintained throughout the year.

The required minimum baseflow in the lower Ord River varies between the wet and dry seasons. Figure 3 shows the required baseflows at the Tarrara Bar station throughout the year; the minimum baseflow is 42 m³/s. Baseflow during the dry season (April–October) is managed almost entirely by water releases from the storages. Figure 3 also shows the frequency, duration, and peak flows required for the wet season flood events in the lower Ord River.

Figure 3 Example water provisions for the lower Ord River; required baseflows and wet season flood events are also shown

The infrequent wet season flood events occur as a result of runoff from the catchment downstream of Lake Argyle and cannot be managed by water releases from the storages. The return intervals for these flood events are greater than 1 in 2 years, so this component of the required flow regime is difficult to evaluate on an annual basis. These flood events are not shown in Figure 3 above.

A more detailed description of the environmental water provisions for the lower Ord River are provided in Chapter 4 of the Ord Surface Water Allocation Plan, including variations to the flow regimes for low rainfall years (determined by water levels in Lake Argyle).

Environmental water outcomes

The mean daily flow at the Tarrara Bar gauging station along the lower Ord River during the 2013–14 year is shown in Figure 4.

For all but one day of the year (1 November 2013), flow in the lower Ord River exceeded the minimum baseflow requirements. Figure 4 also shows that wet season peak flows met the requirements outlined in the water provisions. The only exception was that flow exceeded 125 m³/s on only three separate occasions rather than the required four spells; however, total duration of flow above 125 m³/s for the wet season was 132 days, well above the required 10 days.

Figure 4 Flow in the lower Ord River compared with the required flow regime during the 2013–14 year

Infrequent wet season flood events are the third component of the flow regime critical for maintaining ecological conditions in the lower Ord River (see Environmental water provisions above). One flood peak on 18 January 2014 met the required 1 in 4 year flood event (average daily discharge >1,400 m³/s); a second flood peak on 8 February 2014 met the required 1 in 27 year flood event (average daily discharge >3,700 m³/s). The 1 in 27 year flood peak requirement is the largest in the environmental water provisions. Both of these flood events are described in more detail in the Water overview.