The influence of tide, meteorological conditions and hydrodynamics of fine sediment transport in a macro-tidal estuarine lagoon
With predicted climate change and sea level rise, the understanding of estuarine
systems becomes more critical so as to gain an insight into the stability of the coastal
environment both for environmental and economic reasons. The combined influence of
tide and meteorological effects on the erosion, transport, deposition, consolidation
cycle (ETDC) of intertidal sediment is not well understood. To further the knowledge
into this area an intensive data collection program was conducted in the previously
hydraulically un-investigated, macro-tidal estuarine lagoon at Pagham Harbour,
Monitoring of variations in the elevation of the mudflats indicate that generally accretion
occurs in the west of harbour, with the east acting as source as well as a temporary
storage area for the sediment which is primarily imported from the English Channel
during winter storm periods. The redistribution of the sediment is dependant upon
exposure to predominant wind direction, wind speed and local channel geomorphology.
Monitoring of the water column identified that sediment is moved landward by means of
a peak in turbidity which occurs at the beginning of each flood tide. This sediment
movement is enhanced by tidal pumping caused by saline stratification which occurs at
the onset of each flood tide as a result of a combination of the harbours'
geomorphology and of the control of freshwater input.
Precipitation during low tide causes eroded sediment to migrate towards the channels
of the harbour, and the increase in freshwater discharge moves loosely consolidated
sediment seaward. High freshwater events also retard the advancement of the saline
water, prolonging the duration of the peak in turbidity. The magnitude of the peak is
controlled by tidal range and recent precipitation events.
Calibration of an "off the shelf coastal model highlighted the need for more data
collection so that the accuracy of the prediction of the tidal curve, which directly
influences depth and velocity, can be improved.
Changes in climate and sea level are rendering coastal defences unsustainable, with
management plans becoming outdated at an accelerating rate. Knowledge gained
from these investigations can aid coastal manager to make more informed decisions
for future management strategies in Pagham Harbour and at other coastal sites.