Cumulative Impacts in Water Resource Development

Cumulative impacts occur where decisions made, apparently within the terms of legislation or prevailing policy, produce a series of small scale, individual outcomes that cumulatively have an effect contrary to the original intent of the legislation. We illustrate this problem using three examples. The Victorian Catchment and Land Protection Act (1994) is one of a series of Acts that have made special provision for land use determinations in declared water supply catchments. Ultimately, however, these intentions get put into practice through local council planning schemes where zoning provisions mandate acceptable land uses in any area. Recent decisions by local council planning committees, invariably upheld on appeal, take account only of specific site scale activity. There is no ability within this planning process to take account of the clear intention of the Act to control land use across the wider catchment. Although catchment water resources are finite, water authorities have often been unwilling to impose usage limits until catchment hydrology is at crisis point. This is perhaps most starkly illustrated in the Murray-Darling, where a combination of surface and groundwater entitlements have resulted in gross over-allocation to human needs. Farm dams are invariably small in the context of the larger drainage basins within which they are situated and the smaller of these dams have traditionally been outside the influence of government regulation. Most individual farm dams have non-measurable impacts at the scale at which planning of catchment water resources is undertaken. Collectively, however, farm dams can store and extract a significant proportion of the available resource and may deny access to downstream users and to downstream aquatic environments.