Impact of hydrogeomorphic processes on ecological functions of brown trout habits
2017
Majdzadeh Tabatabai, M. R. | Mousavi Nadushan, R. | Hashemi, S.
In recent decades, due to river regulations and their impact on river morphology, brown trout populations have been declining along Lar River downstream of Lar Dam located near Tehran, Iran. Considering the recent water scarcity in the country, development of river habitat assessment models seems necessary. Therefore, in this research, an analytically applied approach is adopted to evaluate brown trout habitat by creating a relation among the hydrologic, hydraulic, geomorphic and ecologic processes. After field survey, dimensionless shear stress of the stream flow thresholds including environmental flow, bankfull flow, surface and subsurface sediment flow thresholds was calculated for Lar, Dalichay and Sefidab Rivers using Shields formula. Then, by considering the dimensionless shear stress ranges of the stream flow thresholds, functional flows ranges and duration were calculated together with ecological efficiency of the cross sections. In addition, effects of annual water yield and entrenchment ratio of the cross sections on habitat functionality were also worked out as a result of which an exponential interaction was developed between the dimensionless shear stress and discharge. Results show that an increase in functional flows ranges and duration, together with rising of ecological efficiency, is directly proportional to an increase in median bed sediment size, entrenchment ratio and annual water yield. Therefore, flow regime, cross-sectional geometry, water-surface slope and bed sediment size could be effective on the ecological functions of the brown trout’s life cycle and functionality of river flow.
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