Scoping options for the ecological assessment of cold water pollution mitigation downstream of Keepit Dam, Namoi River.
Boys CA, Miles N and Rayner T (2009) Scoping options for the ecological assessment of cold water pollution mitigation downstream of Keepit Dam, Namoi River. Final report prepared for the Native Fish Strategy, Murray-Darling Basin Commission (now Murray-Darling Basin Authority), Canberra, Australia. MDBA Publication 20/09. 52pp. ISBN 978-1-921257-82-7.
Cold water pollution (CWP) remains a significant problem hindering the recovery of native fish populations in the Murray-Darling Basin (MDB). Despite this, of all the factors impacting on native fish, CWP is among the easiest to recognise, quantify in magnitude and extent, and there are several pragmatic solutions available to alleviate its impact. When and where CWP has the potential to be addressed as part of dam safety upgrade projects, research is needed to gauge the degree of ecological improvement that can be gained.
This report examines how documenting fish assemblage responses to CWP mitigation in the MDB can be achieved based on a well-established impact assessment design framework, appropriate sampling equipment and fish assemblage indicators. Specifically, a monitoring program to accompany the installation of a multi-level offtake (MLO) at Keepit Dam (Namoi River) was scoped. The scoping study concluded that a four year program to determine the fish assemblage response to the operation of a MLO at Keepit Dam would cost about $1.2 million, almost half of the proposed works budget. Whilst the maximum 5oC improvement in temperature that is expected downstream of Keepit Dam may have positive effects on the fish assemblage, the response may not be large enough to be cost-effectively measured using the indicators available. Based on this, other suitable locations for a CWP mitigation monitoring and evaluation study need to be explored as possible alternatives to Keepit Dam. The current magnitude of CWP downstream of many storages in the MDB is much larger than what is experienced downstream of Keepit Dam and these other storages may provide better case studies because the potential for thermal improvement is greater. Alternative storages will have to be localities where CWP mitigation works are already being planned (e.g., Burrendong Dam). The design proposed in this scoping report can be equally applied to other large storages throughout the MDB, with only a small amount of additional work being required to apply the design to the site-specific features of habitat, thermal regime and fish assemblage.
The extended drought, record low inflows and very low storage levels currently being experienced in the MDB mean that now is not an opportune time to study fish responses to CWP. However, given that research into CWP mitigation is considered of high priority under the Murray-Darling Basin Authority’s Native Fish Strategy, it is recommended that the opportunity to support such research be re-addressed annually using up-to-date predictions of storage levels and the likelihood of CWP events.