Behaviors of extreme water level in the Pearl River Delta and possible impacts from human activities

Abstract. Trends and variations of the extreme water levels defined as exceeding/falling below certain thresholds (mean ± std) across the Pearl River Delta (PRD) are systematically explored using the linear regression method. Research results indicate that: 1) The upper PRD is dominated by the significant decreasing low water level, and significant increasing low water level can be identified in the lower PRD. The variations of the relative frequency of the high water level are characterized by the decreasing variability in the middle PRD. However more stations show significant changes of the relative frequency of the low water level across the PRD. No confirmative changing patterns of the relative frequency of the low water level can be detected in the middle PRD; 2) When it comes to the seasonal variations of the high/low water level in JJA (high flow periods in the PRD), stations located closer to the estuary tend to exhibit increasing high/low water level. However stations located closer to the upper PRD tend to show decreasing high/low water level. Similar patterns can be identified in the high/low water level in DJF (low flow periods in the PRD); 3) The changes of the water level in the PRD are heavily affected by human interferences, e.g. in-channel dredging, sand mining and the construction of levees. The stations dominated by decreasing water level are mostly located along the river channels featured by highly-intensive dredging. The stations along the coastal regions show significant increasing extreme high/low water level. The coastal regions are not influenced by in-channel dredging, and furthermore, sediment loads from upper and middle PRD are deposited in the river mouths and which will tend to raise the water level in the estuary of the PRD. The findings of this paper may be helpful for local water resource management.