LONG-TERM SPATIOTEMPORAL VARIATION OF SURFACE WATER TURBIDITY IN HAI PHONG BAY, VIETNAM

Hai Phong Bay, situated in Northern Vietnam, has been facing the problem of sedimentation for decades. The Cam river, falling into Hai Phong Bay, brings significant amount of sediments to the bay causing complex turbidity in the area. Since Hai Phong Bay is situated adjacent to Ha Long Bay, one of UNESCO world heritage, monitoring the turbidity in Hai Phong Bay is vital not only to tackle with the sedimentation problem in the bay but also to preserve relatively lower turbidity in Ha Long Bay. This study monitors the turbidity in Hai Phong Bay from 2002 to 2018 using satellite images and measured data. Hai Phong Bay has an area of as large as 550 km(2) and thus it is virtually difficult to capture the spatiotemporal variation of the suspended sediment concentration through in-situ measured data. In such a context, use of satellite images may be one of preferred options. This study uses satellite images of the data archive of Moderate Resolution Imaging Spectroradiometer (MODIS) to capture the spatiotemporal variation of the suspended sediment concentration. The obtained results clearly show a significant reduction of the suspended sediment in Hai Phong Bay after the years of the 2010s. According to the analysis, it was also evident that time-varying turbidity in the western part of the bay is highly correlated with the river discharge unlike the eastern part of the bay. This feature may indicate that sediment transport in the east-west direction is not dominant and the sediment discharge from the river mouth located on the west side of the bay may have relatively less impact on sedimentation in the eastern part of the bay.