River management on a reach basis highlights lagged channel responses to multiple channel disturbances: Yea River and Murrindindi Rivers, Victoria — ASN Events

River management on a reach basis highlights lagged channel responses to multiple channel disturbances: Yea River and Murrindindi Rivers, Victoria (11656)

Wayne D Erskine 1 , ANTHONY LADSON 2 , John W Tilleard 2 , Michael Cheetham 3
  1. Hydrological, Geomorphological and Chemical Processes Group, Environmental Research Institute of the Supervising Scientist, Darwin, NT, Australia
  2. Moroka Pty Ltd, Sommers, Vic, Australia
  3. Watertech, Brisbane, Queensland, Australia

The Yea River and its major tributary, the Murrindindi River are tributaries of the Goulburn River in Victoria. Each river was classified into geomorphologically homogeneous river reaches, six on the Yea River and four on the Murrindindi River. The main distinguishing geomorphological features of each reach have been described and each reach has been used as the basis for identifying river management issues in terms of dominant bio- hydrogeomorphic processes, connectivity between reaches, prognoses for future river behaviour and evolutionary trajectories, and deriving river management plans.

Historically, avulsions have been the most significant river management issue. The lowermost reach on the Murrindindi River (Turnbull avulsive straight reach) has received large amounts of coarse granitic sand since European settlement from gold mining (1850-1920), catchment erosion due to a rabbit plague (1890-1950) and salvage logging following the 1939 conflagration (1939-1944). This sand has now been exhausted. River response to the sanding was multiple avulsions and the supply of large amounts of sand to the Yea River downstream of the junction (Cheviot avulsive meandering reach). Avulsions occurred due to sand aggradation of the channel and the formation of an elevated alluvial ridge above the floodplain. When the channel avulsed off the alluvial ridge into a connected floodplain depression, the main channel rapidly switched from the original to the new channel and the two channels only functioned simultaneously for a short period of time. The recent decrease in sand supply has reduced the incidence of avulsions.

The upper Yea River in the Toolangi meandering reach has a forested floodplain. Minor attempts to 'snag' the channel in the 1930s and 1940s were restricted in extent and the channel has remained stable since then despite predictions of large-scale erosion and the formation of numerous  debris dams. The channel should be left undisturbed. Nevertheless, strawberry production on the surrounding steep hills of marine mudstones has caused accelerated soil erosion and the supply of fine-grained sediment to the channel. Improved agricultural practices are needed to reduce soil erosion and filter strips are required to trap sediment before reaching the integrated channel network.

River reaches are the logical basis for river management. While many river management activities can be applied over large areas (fpr example, riparian fencing, riparian revegetation, large wood recruitment, removal of artificial fish barriers, etc), most management problems (avulsions, sand aggradation, artifical constrictions) have a localised distribution and require more specific mitigative activities.

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