Water quality planning Elliott main channel

[Extract] EXECUTIVE SUMMARY.\ud The Australian Centre for Tropical Freshwater Research (ACTFR) has undertaken a preliminary survey of freshwater environments that could be affected by the proposed construction of the Elliot Main Channel (EMC) and further development of irrigation lands between Home Hill and Bowen. The study was commissioned by the Regional Infrastructure Development group of the Queensland Department of Natural Resources. The objectives of the study were:\ud \ud -To provide an ecological description of the aquatic environments within/downstream of the proposed development, particularly in relation to their water quality and conservation status. \ud \ud -To provide a broad assessment of issues which may affect the aquatic environments. \ud \ud -To provide recommendations for planning purposes and guidance in the mitigation of potential impacts. \ud \ud Following preliminary aerial and ground surveys in late 1997, two seasonal sampling trips were undertaken in 1998. A literature/data search and review of existing information was also conducted during this period. \ud \ud Results show that the streams in the region are highly intermittent, with only one site (Saltwater Creek in Inkerman) considered to be perennial. This creek receives both channel and tail water from an existing irrigation area, and its ecological classification is artificial. This creek also maintains a valuable freshwater wetland downstream, given the paucity of other permanent water bodies in the region.\ud \ud The intermittent creeks vary in their geomorphology, water quality and conservation values. Many reflect the impacts of cattle grazing and cleared lands; however, several have retained their ecological features and provide valuable habitat. The quality of residual water in the creeks is inextricably linked to their flow regimes, and it appears they are particularly influenced by small rainfall events which are insufficient to stimulate flow in the catchment. Similarly, instream processes which can affect individual waterholes (eg. grazing, clearing etc) are currently likely to have much more of an influence on water quality than upstream catchment processes. \ud \ud The conclusions from this study concur with previous ACTFR assessments of other existing or proposed irrigation areas:\ud \ud -Significant releases of irrigation tail waters into any of the intermittent streams in the study area will destroy existing aquatic habitats and result in the establishment of a new modified ecosystem.\ud \ud -During the dry season, sediment and nutrient export loads are currently negligible because the streams do not flow. The introduction of artificial flows will therefore create a massive increase in seasonal loading even if volumes are low and water quality is good.\ud \ud -Aquatic weed invasions will inevitably occur if sufficient water is introduced into the streams to prevent the stream bed from drying out seasonally. This will happen regardless of the quality of water.\ud \ud -Weed invasions will be less rapid and may be more easily controlled if sediment and nutrient concentrations are minimised.\ud \ud -The habitat values and sustainability of the modified ecosystems created by tailwater drainage can be improved by minimising nutrient and sediment concentrations and loads. In some cases this may be partially achieved by minimising tailwater volumes. However, in order to optimise water quality and habitat values once the modified ecosystems become established, it may be necessary to ensure that flow rates are adequate to provide aeration, prevent the development of algal blooms and limit the extent of floating weed assemblages.\ud \ud Recommendations from this study relate to taking precautionary and mitigative strategies in the development of any proposed irrigation area. Essentially, this relates to: \ud \ud -Ensuring best practices are adopted (eg. water use efficiency, nutrient and pesticide use etc).\ud \ud -Protecting valuable environments (eg. directing drainage towards least valuable/susceptible areas). \ud \ud -Preventing impacts (eg. utilising catchment management tools such as constructed wetlands). \ud \ud -Undertaking further studies to better define management objectives (eg. significance of coastal and near-shore environments)