Struktur Saliniti dan Discas Air Tawar di Estuari Sungai Muda

The objectives of the study are to determine the influence of tides on pattern of seawater intrusion into Muda estuary and to examine the effects of monsoon season on characteristics of the estuarine water. Field measurements of salinity and temperature were carried out monthly for a period of one year during spring tides; in addition several measurements were also conducted during neap tides. Based on the obtained salinity pattern, the Muda estuary is categorized as a salt wedge type. The distance of intrusion of the salt wedge was estimated to be 5 km during spring tide. It was found that the fresh water flowed out to the sea within the upper surface layer (between 0.5 m to 1.0 m) of the estuarine water column while seawater flowed into the estuary at the bottom layer. Our results show that this circulation pattern diminishes when the fresh water discharge increases above the average value (50-100 m3s^-1) in the months of October, November and December. It appears that during periods of high discharges the fresh water controls mixing in the estuary. A negative correlation was established between salinity values and fresh water discharge with a value of 0.74, reflecting a typical phenomenon of an estuary situated in the tropical region. This implies that an increase in fresh water discharge into the Muda estuary results in a decrease in the estuarine salinity values and vice versa.