Entitlements, allocations and sustainable yields
Governments, scientists and communities have struggled with how to express whether water systems are achieving a sustainable balance between consumptive use and the environment. A number of key definitions are involved, including:
- A water access entitlement—a perpetual or ongoing entitlement to exclusive access to a share of water from a specified consumptive pool as defined in the relevant water plan (ABS
- A water allocation—the specific volume of water allocated to a specific water resource access entitlement in a given season, defined according to rules established in the relevant water plan (ABS
- Overallocation—situations in which, with full development of water access entitlements in a particular system, the total volume of water able to be extracted by entitlement holders at a given time exceeds the environmentally sustainable level of extraction for that system (NWI definition).
- Overuse—situations in which the total volume of water actually extracted for consumptive use in a particular system at a given time exceeds the environmentally sustainable level of extraction for that system. Overuse may arise in systems that are overallocated, or it may arise in systems where the planned allocation is exceeded due to inadequate monitoring and accounting (NWI definition).
- Environmentally sustainable level of extraction (often referred to as sustainable yield) for a given water management system—the level of water extraction that would compromise environmental assets, or ecosystem functions and the productive base of the resource, if it were exceeded (NWI definition).
Herein lies a major problem. There is no agreed national approach to estimating the environmentally sustainable level of extraction (sustainable yield).
Under the NWI, environmental outcomes for a particular system are identified primarily through the water planning process informed by best available science, socio-economic analysis and community input. Such outcomes must include the maintenance of ecosystem function, and also include targets for matters such as river health, which may vary between systems.
Total channel control in the Macalister Irrigation District, West Gippsland, being shown to industry group
Image by Axel Allgaier, sourced from Sinclair Knight Merz
AWR 2005 has used the estimates of environmentally sustainable levels of extraction or yield as provided by states and territories. To a greater or lesser extent, these estimates indicate the volume of divertible yield after environmental flows have been taken into account, so that extractions and diversions do not compromise environmental assets or ecosystem functions. Importantly, the climate has dried during the past decade over much of southern Australia, so that the use of sustainable extraction or yield values derived from the last half of the last century may no longer reflect sustainable levels of extraction.
The use of the term overallocation as defined under the NWI more accurately refers to over-entitlement or over-development — the situation in which the cumulative volume of water access entitlements at given point in time for a specific system exceeds the environmentally sustainable level of extractions, or sustainable yield for the system. However, each state and territory currently uses different terminology to describe water entitlements and allocations (refer to the NWC
Dictionary of Terms). Jurisdictions have also issued entitlements with differing reliabilities. Reliability represents the frequency with which water that has been allocated under a water access entitlement is expected to be able to be supplied in full. This is described in some jurisdictions as high or low security.
It is possible to identify water management areas (within the 51 priority geographic areas considered, and based on available data) where the water resource was stressed (overused/overallocated, fully allocated or approaching full allocation) during 2004–05. Note that the data for this assessment has been obtained from a range of sources including states and territories, the Level 1 AWR 2005 assessment, the Level 2 AWR 2005 water balances for the priority areas, Water Entitlements, Allocations and Trade (ABS 2006) and the Water 2010 project (BRS 2006).
Because of the potential confusion regarding definitions and the fact that sustainable levels of extraction may need revision for many systems, as well as identifying overallocation and overuse, several water resource development ratios that identify stress on the water resource were also considered. These include:
- consumptive use as a proportion of inflows
- consumptive use as a proportion of the water resource
Water management areas defined herein as overused/overallocated or under a high level of water resource development, are likely to be under the greatest stress. Under the 2004–05 entitlement, allocation or use regimes, this may affect either security of supply for productive users or ecosystem functions.
The integrated assessment is discussed in more detail in the following sections: