Towards a comprehensive river barrier mapping solution to support environmental management

The environmental effects of large dams on river connectivity are well recognized and mapped globally. However, datasets describing the distribution and attributes of smaller barriers (such as weirs and culverts) are lacking or incomplete for many regions. This has hindered accurate impact assessments for water resource planning, biased understanding of restoration potential and limited research aiming to understand and mitigate river fragmentation effects. Developing an efficient method to accurately record river barriers, including small ones, has become a priority. We critically examine barrier mapping approaches, from field survey to automated detection, showcasing recent approaches to recording, counting and classifying river barriers. We demonstrate how incomplete barrier databases, particularly those lacking many small barriers, provide a flawed basis for water management and ecological restoration planning. We discuss the efficiency and accuracy of alternative barrier mapping approaches, highlight future priorities and emphasize harmonizing barrier assessment methods to generate reliable, freely available information for effective basin-level management.