The impact of creek formation and land drainage runoff on sediment cycling in estuarine systems

Abstract

Field investigation and empirical analysis were used to assess the impact of tidal creeks and tidal flap gates (through which land surface runoff drains into estuaries) on sediment transport in the receiving waters downstream of the creeks and propose a semi-empirical model to assess the impact of water level rise and increased runoff flow, as may be expected under many climate change scenarios.Results show that there is increased suspended sediment concentration (SSC) at low tide within the deeper channel downstream of the tidal flap gate. This is due to the high SSC that is ejected by the creek because of land drainage runoff with SSC in the creek ranging from 47 mg/l to 300 mg/l at spring ebb tide and that in the deeper channel ranging from 22 mg/l to 104 mg/l. This effect was more pronounced at spring tides when the water level in the deeper channel was low. Substantial sediment is supplied by the creek on a spring low tide than a neap low tide due to higher exposure period of intertidal flats for spring low tides. The combination of creeks and tidal flap gates has the highest impact on SSC in the deeper channel at low tide and high surface runoff flow.It is recommended that moving forward on developments around coastal areas, management authorities create more effective and sustainable drainage systems with less impact on estuarine environments to protect aquatic life and promote habitat creation for a sustainable future. Such systems whereby there are numerous drainage flaps surrounding estuaries especially in intertidal flat areas should be transformed into systems with fewer secondary effects on estuarine environments.