Channel recovery in a regulated river: Effects of an experimental and natural flood in the Snowy River, SE Australia

Experimental floods, generated downstream of dams, are used to recover specific bio‐geomorphic functions in regulated rivers. Studies of the effects of experimental floods vary in their objective, location, and the hydrological and bio‐geomorphic variables used to quantify recovery. Measurements of geomorphic change are required to guide future release strategies. The focus of this study was to determine if a large experimental flood in the Snowy River Australia, could promote geomorphic recovery of the river channel downstream of Jindabyne Dam following 35 years of flow regulation. The objectives of the release were to deepen, widen, and increase channel capacity and coarsen the riverbed substratum in the Jindabyne Gorge and Dalgety Uplands sections of the Snowy River. Data from the release were compared with that of a natural flood event that occurred after the experimental flow event. Both events showed channel adjustments and a degree of geomorphic recovery, but this varied between the two river sections. Marked channel adjustments occurred in the Dalgety Uplands reach following both the experimental and natural flood event and in the Jindabyne Gorge section following the natural flood event. Geomorphic changes were related to the hydrological character of each flood event. The number of flood peaks, the sequence of peaks, the flood duration, and the total energy expenditure differed markedly between the two events, and these four flood hydrological characteristics explained the greater geomorphic recovery associated with the natural flood event in the Jindabyne Gorge. No clear hydro‐geomorphic relationship was derived for channel change in the Dalgety Uplands where existing morphological constraints limit flood effectiveness.

[1]  V. Baker,et al.  Flood power , 2020, Catastrophic Flooding.

[2]  W. Erskine,et al.  Bedform maintenance and pool destratification by the new environmental flows on the snowy river downstream of the Jindabyne Dam, New South Wales , 2017 .

[3]  M. Delong,et al.  Physical heterogeneity and aquatic community function in river networks: A case study from the Kanawha River Basin, USA , 2017 .

[4]  D. Gilvear,et al.  River Science: Research and Management for the 21st Century , 2016 .

[5]  M. Delong,et al.  An ecosystem framework for river science and management , 2016 .

[6]  Simon Williams,et al.  Mobilising fine sediment in a highly regulated upland snowmelt river using hydrological scaled experimental floods , 2016 .

[7]  R. Jacobson,et al.  The Natural Sediment Regime in Rivers: Broadening the Foundation for Ecosystem Management , 2015 .

[8]  Timothy J. Randle,et al.  Flood Releases from Dams as Management Tools: Interactions between Science and Management , 2013 .

[9]  J. O’Connor,et al.  Geomorphically Effective Floods , 2013 .

[10]  Alison J. King,et al.  Environmental flow enhances native fish spawning and recruitment in the Murray River, Australia , 2009 .

[11]  Ellen Wohl,et al.  Characterizing environmental flows for maintenance of river ecosystems: North Fork Cache la Poudre River, Colorado , 2009 .

[12]  S. Darby,et al.  Monitoring and numerical modelling of riverbank erosion processes: a case study along the Cecina River (central Italy) , 2009 .

[13]  Damià Vericat,et al.  Hydrological and sediment transport dynamics of flushing flows: implications for management in large Mediterranean Rivers , 2009 .

[14]  Ian C. Fuller,et al.  Geomorphic impacts of a 100-year flood: Kiwitea Stream, Manawatu catchment, New Zealand , 2008 .

[15]  J. David Allan,et al.  River Restoration in the Twenty‐First Century: Data and Experiential Knowledge to Inform Future Efforts , 2007 .

[16]  J. Hooke,et al.  A simulation model of morphological, vegetation and sediment changes in ephemeral streams , 2005 .

[17]  K. Pye,et al.  GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments , 2001 .

[18]  Paul E. Grams,et al.  THE 1996 CONTROLLED FLOOD IN GRAND CANYON: FLOW, SEDIMENT TRANSPORT, AND GEOMORPHIC CHANGE , 2001 .

[19]  W. Erskine,et al.  Recovery of the Snowy River: Politics and River Rehabilitation , 1999 .

[20]  L. James,et al.  Geomorphic and Sedimentological Controls on the Effectiveness of an Extreme Flood , 1998, The Journal of Geology.

[21]  Carl Richards,et al.  Landscape-scale influences on stream habitats and biota , 1996 .

[22]  J. Pitlick.  Response and recovery of a subalpine stream following a catastrophic flood , 1993 .

[23]  F. Magilligan.  Thresholds and the spatial variability of flood power during extreme floods , 1992 .

[24]  W. Graf.  Downstream Changes in Stream Power in the Henry Mountains, Utah , 1983 .

[25]  M. Wolman,et al.  Magnitude and Frequency of Forces in Geomorphic Processes , 1960, The Journal of Geology.

[26]  J. Hooke.  Morphological impacts of flow events of varying magnitude on ephemeral channels in a semiarid region , 2016 .

[27]  W. Erskine,et al.  Sedimentological and geomorphological effects of the 1997 and 1998 flood sequence on the lower Snowy River, Victoria. , 2016 .

[28]  K. Fryirs,et al.  Working with Change: The Importance of Evolutionary Perspectives in Framing the Trajectory of River Adjustment , 2008 .

[29]  Wayne D. Erskine,et al.  River rehabilitation from the hydrogeomorphic impacts of a large hydro‐electric power project: Snowy River, Australia , 1999 .

[30]  V. R. Schneider,et al.  GUIDE FOR SELECTING MANNING'S ROUGHNESS COEFFICIENTS FOR NATURAL CHANNELS AND FLOOD PLAINS , 1989 .