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

Abstract

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. KEYWORDS channel maintenance flows, conceptual model of channel adjustment, environmental flows, flushing flows, geomorphic recovery

Riverine landscapes, water resource development and management: A view from downunder

“…The construction of dams and subsequent alteration to downstream flow and sediment regimes has had irreversible effects on river ecosystems. The study by Rose, Erskine, and Miners (2020a) develops a model that determines the geomorphic effectiveness of small floods in a regulated Australian river and shows how this can ameliorate specific geomorphic impacts in reaches downstream of dams. The complementary case study by Rose, Erskine, and Miners (2020b) shows how experimental releases from dams can be used to quantify recovery in downstream‐regulated reaches.…”

Long‐term environmental flows restore benthic invertebrate communities in a highly regulated river

“…Furthermore, the relative abundances of one filter feeder (Coloburiscidae) increased at all sites. These patterns may have occurred because higher flows altered environmental conditions by expanding the area of fast‐flowing habitat (Rose et al 2020 b ), creating more space and increasing food resources. Higher flows may have increased the amount, quality, and availability of adult oviposition substrates for egg‐laying adults (emergent rocks in fast flows) resulting in proportionally higher filter feeder abundances via greater recruitment (Reich 2004; Encalada & Peckarsky 2012; Lancaster & Downes 2014).…”

Hydromorphological response of heavily modified rivers to flood releases from reservoirs: A case study of the Spöl River, Switzerland

“…Despite the importance of flood events to river health, examining their hydromorphological impacts has been largely ignored in e‐flow studies (Gregory et al, 2018; Rose et al, 2020; Wohl et al, 2015). Moreover, it remains a challenge to understand how flood characteristics (e.g.…”