Scotts Creek Spawning Enhancement
Mark Webb, Fish and Game Officer.

Scotts Creek is an important spawning stream which flows into Lake Alexandrina.  A 1.5 tonne excavator was used to alter flow characteristics of the creek to better suit trout spawning. The work was completed on 10/11 March and involved increasing the water velocity in deep slow sections of the creek. This was achieved by two means – narrowing stream width and/or reducing the height of the downstream hydraulic control which was usually the riffle at the downstream end of the pool.  By dragging shingle upstream into the pool, pool depth was reduced  and by using some of the gravel to create new banks the pool width was reduced. The new gravel lined banks will also reduce silt intrusion into the stream by preventing erosion of the bank by stream flow and trout activity. Overall we have  improved spawning in about 400 m of the 600m of stream above the hut settlement.

The flow of Scotts Creek appears to be reducing year by year and while not obvious as an annual increment, taken over decades the reduction is significant. Reduced flow equates directly to less spawning habitat. In the 20 years I have been working on Scotts Creek the average flow has probably reduced by one-third but this has really only become noticeable with recreation of a uniform streambed in 2005 as it was in 1986 through regravelling. We did not recognize this problem when we regravelled in 2005 and the same stream width was used as in 1986. The result being a streambed that in places was too wide and too shallow for trout spawning and this was the second issue. The first issue we are unlikely to be able to rectify without flow augmentation and this is a long term option. In the short term, by adding gravel to reduce stream width we can still create good water depth and velocity for spawning with the flow available. This is likely to be the focus of our habitat work in March 2009 and if successful we would see regular maintenance of stream width being sufficient to retain spawning habitat through to the next regravelling in about ten years time.

The stream currently lacks escape cover for adult trout.  Planting of Carex secta on the west bank will provide good overhead cover and spawning trout will find some security as the plants mature.

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