Measuring the extent of the threat to river and stream ecosystems in NSW from water extraction
Rivers and streams are acknowledged as one of the most imperilled of global ecosystems yet are not effectively conserved by existing protection measures that almost always lack a catchment focus. One of the major threats to rivers is the extraction of water for consumptive uses. Using water extraction licence data supplied by the NSW Department of Natural Resources we calculated the total upstream water allocation for all of the rivers and streams in NSW and compared this to estimates of annual mean natural flow computed from a simple catchment water balance model for each of the years 1970 to 2004. We also considered the variability of natural flows by determining the proportion of flow allocated in both dry and wet years (the 10th. and 90th. percentiles of the modelled annual flows respectively). Information was computed for each stream segment (link) and summarized for drainage basins.
Unavoidably, this analysis contains significant uncertainties due to limitations of the catchment water balance model and the representation of drainage patterns, especially in distributary and floodplain systems. Nonetheless, the analysis provides a statewide comparative indication of the threats from water extraction to rivers and stream ecosystems. It identifies the rivers under greatest stress, particularly in drier years where many rivers and creeks appear to be over-allocated. Included among these are many within protected areas highlighting the difficulties of protecting rivers in reserves where reserve managers have no control on water use upstream. Free-flowing rivers are globally rare. This analysis confirms this is also true in NSW where very few river systems were found to be entirely free of the threat from water extraction from source to mouth (or terminal lake) and none among larger rivers. Assessing the conservation value and options for protection of the remaining free-flowing rivers must be a priority.