Seasonal variations of sediment load related to all large damming in the Red River system: A 64‐year analysis

Abstract

Variations of water discharge and sediment load in the Red River basin have received considerable attention due to its drastic reduction during the past several decades. This paper presents a more specifically investigating of the seasonal variations in water discharge and sediment load from 1958 to 2021, both before and after the impoundment of all large dam‐reservoirs, using daily observations from the Son Tay hydrological gauging station, the outlet of the Red River system and entry to the delta. Sediment loads have decreased progressively since the early 1990s due to sediment yield reduction and dams in the upper basin, with a reduction of about 91% (from 116 × 106 to 11 × 106 t/year) over the 64‐year observation period. Prior to the impoundment of the Hoa Binh dam‐reservoir in 1988, the hydrological processes in the Red River system exhibited seasonal anomalies (clockwise mode on the hysteresis of rating curve), which implies that sediment load is highly proportional to water discharge and precipitation. The hysteresis loops between mean monthly water discharge and suspended sediment concentration after 1988 were altered by tributary dam‐reservoirs and a phenomenon known as ‘temporal monsoon moving’, which shifted the rating curve from clockwise to counterclockwise mode. Our long‐term analysis indicates that approximately 57.5% and 79% of sediments were trapped during the periods 1989–2008 (after Hoa Binh dam‐reservoir impoundment) and 2009–2021 (a series of new dam‐reservoirs went into operation), respectively, primarily during the high‐discharge months (June–October). Additionally, we concluded that the contribution of climate components (e.g., rainfall) to the dramatic decline in sediment load of the Red River system was less than the human impact.