The Gordon River has a large catchment area, most of which lies within the Tasmanian Wilderness World Heritage Area. The Gordon catchment is largely undisturbed forest, and there are numerous large inflows into the 78km reach downstream of the Gordon Power Station. Prior to the Basslink investigations, little was known about the environmental condition of this reach of the Gordon River due to its remoteness and the logistics of access including helicopter access and complete power station shutdowns. A major challenge for researchers was to understand the river system adjustments to present power station operations, which in many cases were still occurring, so that projections of Basslink changes could be made against the baseline of present impacts.
The major issues of concern with the projected changes to Gordon Power Station operations under Basslink were the downstream effects on World Heritage Area values; reduction in habitat availability for macroinvertebrate and fish communities; follow-on effects due to reduced food supplies for fish, platypus and native water rats; projected further erosion of alluvial sediment banks; and a projected acceleration of vegetation losses in riparian zone. The investigations found that all present and Basslink-projected impacts were greatest in the first 15km downstream of the power station, upstream of the Denison River, a major unregulated tributary.
In response to the research findings, Hydro Tasmania made two commitments to address Basslink impacts in the Gordon River. These commitments were to maintain a minimum environmental flow of 19 m3/s in summer and 38 m3/s in winter to maintain habitat area for macroinvertebrates and ensure adequate food supplies for fish and aquatic mammals; and to implement a rampdown rule to address the risks of increased river bank erosion.