ИСТИНА

The Goloustnaya River is a tributary to the Lake Baikal, flowing into the lake at the southwestern shoreline and forming a delta that covers the area of about 13 sq. km. Positioned exactly across the lake from the largest lake Baikal tributary – the Selenga River, the Goloustnaya River shows contrasting hydrological and hydromorphological conditions, which determine the nature of streamflow discharge and sediment distribution in the deltaic channels. The distributary network, consisting only of 3 active channels, and linear size of this delta allows for easy access and rapid flow measurements over each of them, thus serving as a great natural lacustrine hydrology laboratory. In the 2022 we conducted a field campaign to research the discharge and sediment distribution in the deltaic channels. For this we installed a network of automatic water level loggers accompanied by streamflow discharge measurements. The Onset Hobo U20L loggers were installed in the deltaic channels and the streamflow discharges were measured under three conditions: spring freshet rise, early summer freshet ebb and late summer low flows. This setup allowed for characterization of deltaic channel distribution along with water turbidity and dissolved solids measurement. Water balance computation between the distributary channels and the main stream reveals that during higher flows the channels distribute less stream flow than is measured in the delta apex, and in the low-flow conditions the opposite effect is observed. This effect is explained by saturated flow conditions in coarse highly permeable deltaic deposits during different streamflow conditions. This shows that unlike other river deltas on the Lake Baikal, the Goloustnaya River estuary can be characterized as an alluvial fan rather than a delta. This is further confirmed by channel morphology measurements also carried out during the field campaign.