Wapienica dam as a contributing factor in (dis)connectivity associated with sediment transfer in mountain river catchment (Poland)

The construction of reservoirs and associated river regulation, on the one hand, positively affects human quality of life and related economic considerations (i.e. construction of drinking water reservoirs, storage of water for farmland irrigation purposes, flood prevention measures), but on the other hand constitutes a major form of interference in the environment by generating irreversible changes in its functioning. One key impact of reservoir construction is the severance of natural connectivity in the river channel upstream of the dam. This leads to a disruption in the dynamic equilibrium of the river due to the accumulation of sediment upstream of the reservoir’s dam, limited sediment outflow from the reservoir, and increased downcutting downstream of the dam. The main aim of the present study is to examine the impact of a midsize reservoir and dam located along an upstream part of a mountain river and associated river engineering structures on the Wapienica River on (dis)connectivity in terms of sediment transfer.

The Wapienica river catchment area has an area of 51.36 km² and is located in southern Poland (Śląskie Province). It has a longitudinal shape and runs from south to north across three geographic mesoregions – Beskid Śląski Mountains, Śląskie Foothills, Upper Vistula Valley. Each mesoregion is characterized by different relief, land use, and climate, all of which help determine a different rate of change of erosional processes in each of the studied regions.  The construction plan for the Wapienica Reservoir was created in 1911 in response to growing drought conditions in the region and increasing water usage by textile plants operating in the region. The reservoir was to  perform three distinct functions – water storage, flood control, and creation of a key source of drinking water for area residents. Construction work on the reservoir was completed in 1932.

Archived materials and maps, orthophotomaps  as well as a digital elevation model (DEM) with a resolution of one meter were examined in the study along with survey data on suspended sediment accumulation sites along the river. In addition, the Connectivity Index tool in ArcMap software was used, as well as the Soil and Water Assessment Tool (SWAT).

The internal structure of the studied catchment has changed due to strong human impact in the form of reservoir construction in the upstream part of the catchment and regulation in the river channel of the Wapienica along its entire length. This has made it possible to identify six zones characterized by different degrees of structural and functional connectivity.