Abstract

Abstract. The Hoa Binh dam (HBD), located on a tributary of the Red River in Vietnam, has a capacity of 9.45 × 109 m3 and was commissioned in December 1988. Although it is important for flood prevention, electricity production and irrigation in northern Vietnam, the Hoa Binh dam has also highly influenced the suspended sediment distribution in the lower Red River basin, in the delta and in the coastal zone. Its impact was analysed from a 50-year data set of water discharge and suspended sediment concentration (1960–2010), and the distribution of water and sediment across the nine mouths of the delta was simulated using the MIKE11 numerical model before and after the dam settlement. Although water discharge at the delta inlet decreased by only 9%, the yearly suspended sediment flux dropped, on average, by 61% at Son Tay near Hanoi (from 119 to 46 × 106 t yr−1). Along the coast, reduced sedimentation rates are coincident with the lower sediment delivery observed since the impoundment of the Hoa Binh dam. Water regulation has led to decreased water discharge in the wet season (−14% in the Red River at Son Tay) and increased water discharge in the dry season (+12% at the same station). The ratios of water and suspended sediment flows, as compared to the total flows in the nine mouths, increased in the northern and southern estuaries and decreased in the central, main Ba Lat mouth. The increasing volume of dredged sediments in the Haiphong harbour is evidence of the silting up of the northern estuary of Cam–Bach Dang. The effect of tidal pumping on enhanced flow occurring in the dry season and resulting from changed water regulation is discussed as a possible cause of the enhanced siltation of the estuary after Hoa Binh dam impoundment.

Highlights

  • Asia and Oceania contribute 70 % of the global sediment supply from land to the ocean (Milliman and Syvitski, 1992; Farnsworth and Milliman, 2003)

  • This paper aims at complementing the previous studies both in the Red River basin and in its delta before and after Hoa Binh dam (HBD) impoundment

  • The estimates of water and sediment discharge can be improved in the future, this paper is the first to provide the distribution of water and sediments within the nine distributaries of the Red River, one of the biggest rivers in the world

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Summary

Introduction

Asia and Oceania contribute 70 % of the global sediment supply from land to the ocean (Milliman and Syvitski, 1992; Farnsworth and Milliman, 2003). Sediment discharge decreased from 480 to approximately 150 × 106 t yr−1 over a 20-year period in the Yangtze River (Changjiang) (Yang et al, 2006; Wang et al, 2008) and from 1080 to 150 × 106 t yr−1 over a 40-year period in the Yellow River (Huanghe) (Wang et al, 2007). Large rivers and their deltas in Southeast Asia have been impacted by other human activities such as groundwater pumping, irrigation, dredging and deforestation (Tran et al, 2004; Saito et al, 2007)

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