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"June 1996".Project Number: Strategic management plan for the Severn River and tributaries - YH/6/14.MDFRC item.The Severn River and its tributaries were assessed on the basis of a single site visit in April 1996 The scope of the assessment was to investigate the condition of the riparian and instream environment, and to make recommendations concerning their future management. Instream conditions were assessed overall as good to satisfactory, with medium levels of disturbance noted. A major alteration to instream conditions was the large number of weirs, which can obstruct fish passage, affect flows and locally alter instream habitat. Dredging for tin mining was a major cause of disturbance in the past. 15 species of fish have been recorded in the system, including three native species which were not originally found above the falls in Sundown National Park, and possibly 3 introduced species. The riparian vegetation is al so in moderately good condition, with slight impacts evident from introduced weed species such as blackberries and honeysuckle, and local impacts from grazing. The major concerns for both instream and riparian environments is depletion of flows by extractions from in-stream weirs and from impoundments in the catchment. This has an effect on volume and on timing of flows. Long periods of low base flow reduce the available instream habitat by reducing the wetted area available to fish and aquatic invertebrates. The reduction in flood frequency can have serious effects on spawning and fish movement, and on the movement of sediment and organic matter within the stream. The low flows and loss of frequent small floods also has an impact on the riparian vegetation, which depends on the additional water supply to maintain a distinct riparian community, and to allow riparian species to successfully compete with invading dryland species. Pike Creek has a more natural flow regime, but suffers greater impact from grazing with reduction in riparian vegetation, and loss of habitat. The Severn River Trust has an opportunity to become a major advocate for the Severn River system, as the issues are largely catchment issues, with competing interests for water use which can have far-reaching effects on the river environment. Summary of Major Recommendations.- Further water extractions from the Severn River system should only occur after a more detailed analysis of present and natural (pre-extraction) flow regimes, the environmental impact of these and the preparation of a Water Management Plan.- The importance of high flows and small floods to both the in stream habitat and the riparian zone should be recognised, - Any further weir construction, and modifications to existing weirs, should include attention to the requirements of fish passage.- A detailed survey of the fish in the Severn River system should be carried out as part of an ecosystem condition assessment. European Carp, if not already present, should be kept out of the Upper Severn River at all costs.- An education program about the threat of Carp to the system should be undertaken as a matter of urgency. A campaign to increase awareness of the potential problems associated with the use of Carp and Mosquito Fish as live bait should also take place.- Management and protection of the riparian zone should become an important component of good property management.- The riparian zone should be fenced where necessary and grazing should be discouraged.- Attention to weed control in the riparian zone should be sufficient to prevent a minor problem from becoming a major issue. |
