Tidal influence on the discharge distribution over the Pearl river Delta, China

Abstract

The discharge distribution is influenced by the tidal behaviour at tidally affected junctions. The Pearl River Delta (PRD) is one of the most complicated deltas and highly affected by human interventions. The tides are reinforced by the riverbed downcutting caused by intensive sand dredging in the PRD. While some efforts have been made to interpret flow division at the apex of the delta, little attention has been paid to the role of tides on discharge distribution. A 2D hydrodynamic model covering the entire PRD has been established and applied to quantify the tidal influence on subtidal flow division at the tidal junctions. The discharge asymmetry index is introduced to quantify the subtidal discharge division. The method of factor separation is used to decompose the subtidal discharge into the contributions of tides, river discharge and river-tide interactions. Results indicate that the tides alter the allocation of river discharge over distributary channels in the PRD, especially in the dry season. Generally, the effect of tides is to reduce unequal subtidal flow division that occurs without tides. The tidal influence increases seaward with a maximum value of the order of 110% in the dry season, which indicates that the tidal influence on the flow distribution can overwhelm the impact induced by river discharge only. Sensitivity analyses also demonstrate that the tidal constituent M2 makes the largest contribution on flow division at junctions, followed by K1, O1 and S2. In addition, the tidal influence is more apparent due to the increased water depths caused by long-term and extensive sand excavations.