Evaluating the Effects of River Crossings on Fish Habitats and Connectivity

With the growth of urban populations, it has become necessary to develop new urban areas as well as to utilize rivers as water supply resources, which directly impacts human life. Weirs, which are structures built across rivers to regulate stream flow, facilitate human water usage, such as water supply and water level regulation. However, they directly alter the cross-sections of rivers, significantly affecting hydraulic parameters such as flow velocity and water depth. This leads to changes in aquatic habitats, reducing their biodiversity and altering the habitat connectivity of aquatic organisms. This study analysed the changes in habitat connectivity of rivers inhabited by diverse fish populations, considering the presence of weirs, flow regimes and fluvial geomorphological characteristics, to help establish eco-friendly riverine environments that support the coexistence of nature and humans. The analysis revealed that the habitat area, depending on the presence or absence of weirs, varied depending on the flow regime and patch size. In drought flow conditions with smaller patches, the habitat area was larger in the presence of weirs. Conversely, in conditions with flow rates at or above low flow and larger patch sizes, the habitat area was larger without the presence of weirs. Additionally, considering fluvial geomorphological characteristics, sections with medium or low sinuosity and bed slope exhibited a larger preferred habitat area in the absence of weirs. The findings of this study contribute to improving aquatic ecosystem connectivity through the evaluation of habitat connectivity changes based on the presence of weirs and flow regime variations.