Check dams decrease the channel complexity of intermediate reaches in the Western Carpathians (Czech Republic)

Check dams can modify local channel and sedimentological characteristics through sediment deposition in upstream sedimentary wedges and scour processes downstream of individual check dams. However, research focusing on the channel reaches between subsequent check dams (referred to here as intermediate reaches) is limited. We evaluated channel complexity and its selected dimensions (longitudinal and cross-section heterogeneity, sediment characteristics and the presence of instream wood) in 30-m long intermediate reaches (n = 10) between subsequent check dams in comparison with channel reaches that were not treated with check dams (n = 10) in both a stepped-bed stream in a steep confined valley and an originally pool-riffle stream in an unconfined foothill valley. Check dams altered the channel complexity of intermediate reaches when compared with reaches of undisturbed streams. However, in contrast to foothills streams, check dams did not heavily affect longitudinal or cross-sectional heterogeneity of the intermediate reaches in the steep streams. Despite an increase in sediment homogeneity in steep reaches treated with check dams, the presence of coarse bed sediments helped to preserve their stepped-bed morphology. In contrast, the longitudinal profile of the treated foothill stream completely lost its vertical oscillations because of the transformation of pool-riffles to a uniform plane bed morphology. Similarly, cross-sectional heterogeneity in the foothill stream was degraded in comparison with those of untreated reaches. We did not observe differences in instream wood abundance between treated and untreated streams.