Estuarine dams and weirs: Global analysis and synthesis

Estuarine dams and weirs are constructed in estuaries for reasons such as blocking the salt intrusion, securing freshwater, and stabilizing upstream water levels. While they can provide many social benefits, they can also alter estuarine physical and sedimentary processes. How this occurs and their relative importance to global estuaries and deltas are not well understood. To address this, we perform and extensive remote sensing and literature analysis. Remote sensing was conducted based on a global river database of 1531 rivers representing the largest rivers cumulatively draining 85 % of the landmass discharging into the global ocean. It was found that 9.7 % of global estuaries and deltas are currently affected by estuarine dams or weirs acting as the upstream limit of salt, tide, or storm surge intrusion. If we include supplementary examples, overall 220 estuaries with estuarine dams or weirs were identified and confirmed by literature review. These structures are found worldwide and are prominent in developed or developing countries in Asia, Europe, North America, and Oceania. The number of estuarine dams and weirs has increased rapidly since the 1800s with a peak in construction rate in the 1970s, particularly due to construction in Asia. Estuarine dams and weirs are found at the river mouths of both small and large watersheds. Most of these estuarine structures are located at x = 0–100 km inland from the mouth and their discharge intervals can be continuous, daily – weekly, seasonal, or interannual. Based on a quantified classification by geomorphology, estuarine dams and weirs are found most in river mouths which are wave-dominated followed by tide-dominated and then river-dominated. Estuarine dams and weirs can cause significant changes to the quantity and timing of freshwater discharge, tides, stratification, turbidity, sedimentation, oxygen conditions, phytoplankton blooms, and fish migration. We synthesize this current knowledge on estuarine dams and weirs and propose a conceptual model for physical and geomorphological change in mixed wave- and river-dominated and tide-dominated estuaries with estuarine dams.