Suspended solids transport dynamics in regulated rivers
Gilvear, David J.
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Suspended solids, turbidity and discharge data for thirty-seven reservoir releases, three major periods of dam overspill, and 20 unregulated tributary flood events, on seven different river systems, are analysed in order to examine suspended solids transport dynamics within regulated rivers and to assess the effectiveness of reservoir releases material. Within Great Britain, two sudden releases of water to the in removing within-channel accumulations of out of every five major reservoirs cause regulated river. Reservoir releases also provide, with their fixed and constant discharges, a unique opportunity to undertake field experiments investigating the importance of channel suspended solids sources, suspended solids supply limitation, the nature of the suspended solids load on turbidity and flow routing within upland boulder bed channels. The reservoir release suspended solids loads relate to sediment source depletion and changing sources along the channel. Close to the· dam, suspended loads are usually small with fine organic matter dominating the seston, which. scanning electron microscopy revealed to be predominantly autochthonous organic matter, with algal fragments derived from extensive and ·rapid periphyton growth within the regulated rivers. Downstream, minerogenic particles dominate the seston. This represents the flushing of channel bed accumulations derived from· unregulated tributaries. Seasonal variation in the nature of the suspended solids loads is also revealed. The quantity of material transported relates to the relationship between reservoir release or dam overspill frequency and that of unregulated tributary flood events. Marked hysteresis between suspended solids transport and discharge was characteristic on all the regulated rivers. In addition, hysteresis in the relationship between turbidity and suspended solids concentrations was also apparent, this relating to spatial and temporal changes in seston composition. Finally, the results obtained allow not only the nature of suspended solids transport within regulated rivers to be described and the effectiveness of reservoir releases for flushing in-channel accumulations of material to be ascertained but also the formulation of management guidelines and recommendations. These guidelines relate to effective environmental management of regulated river habitats in rivers experiencing reservoir releases.