Dams on the Mekong: Cumulative sediment starvation

TLDR

The Mekong River, largely undeveloped before 1990, is now experiencing rapid dam construction, with seven dams underway on the mainstem in China and 133 proposed for the Lower Mekong and its tributaries. The authors delineated nine geomorphic regions, estimated sediment yields from geomorphic and tectonic characteristics, and used the 3W model to compute cumulative sediment trapping by dams, incorporating time‑varying trap efficiency and multiple dams per system. Under a scenario of 38 dams, sediment reaching the Delta would be reduced by 51 %; full build‑out would trap 96 % of sediment, leaving only 4 % to reach the Delta, threatening Delta productivity and landform stability and underscoring the need for sediment‑passage strategies.

Abstract

Abstract The Mekong River, largely undeveloped prior to 1990, is undergoing rapid dam construction. Seven dams are under construction on the mainstem in China and 133 proposed for the Lower Mekong River and tributaries. We delineated nine distinct geomorphic regions, for which we estimated sediment yields based on geomorphic characteristics, tectonic history, and the limited sediment transport data available. We then applied the 3W model to calculate cumulative sediment trapping by these dams, accounting for changing trap efficiency over time and multiple dams on a single river system. Under a “definite future” scenario of 38 dams (built or under construction), cumulative sediment reduction to the Delta would be 51%. Under full build‐out of all planned dams, cumulative sediment trapping will be 96%. That is, once in‐channel stored sediment is exhausted, only 4% of the predam sediment load would be expected to reach the Delta. This scenario would have profound consequences on productivity of the river and persistence of the Delta landform itself, and suggests that strategies to pass sediment through/around dams should be explored to prevent the consequences of downstream sediment starvation.