Tide and river influences on distributary channels of the Mekong River delta

Abstract:

The Mekong River delta, one of the world’s largest deltas, has extended from Phnom Penh in Cambodia (apex) to the coast from the Saigon River mouth to Cape Camau in Vietnam with a triangular-shape area of more than 60,000 km². The delta has prograded more than 200 km over at least the last 6–7 ka. The river-mouth area of the delta is meso-tidal with the mean tidal range of 2.5 ± 0.1 m and the maximum tidal range is 3.2–3.8 m. The mean wave height is 0.9 m. Its water discharge is 470 km³/y and its sediment discharge is 160 million t/y, or tenth and ninth largest in the world, respectively. The water discharge varies by season because most of the drainage area is under a monsoonal tropical regime. The flow at Phnom Penh, Cambodia, reaches a maximum in October (typically 39,000 m³/s) and a minimum in May (about 1700 m³/s). Tidal water-level changes are observed in Cambodia, more than 200 km upstream from the river mouth.

To understand the combined influenced of river and tide on river bottom sediments, we have collected ~210 surface samples from river bottoms of the whole Mekong River delta in Vietnam, covering five distributaries during dry season from January to May 2015. Sediment characteristics show clearly tide- and river-influenced areas, which are closely linked with river morphology.