Zaki Zainudin

Southwest monsoon influences the water quality and waste assimilative capacity in the Mandovi estuary (Goa state, India)

The monsoon-dominated Mandovi estuary is located in Goa state – a global tourist destination along the centralwest coast of India. In addition to factor analyses of water quality data, the water quality index (WQI), trophic state index (TSI) and percentage of freshwater volume in the estuary are calculated in order to infer the general waste assimilative capacity and prevailing water quality conditions. Factor analysis showed a dominance of PO4–P, NO2–N, NH3–N, total suspended solids (TSS) and turbidity during southwest (SW) monsoon relative to other seasons. The WQI suggested that an increase in nutrients, turbidity and TSS during SW monsoon increase the WQI values beyond 2, rendering the water at some locations slightly polluted. During pre-monsoon, considerable increase in the WQI is observed at all the upstream stations rendering slightly polluted water at these stations. The TSI showed an average value of 46.95 during SW monsoon, 42.43 during post-monsoon and 48.42 during the pre-monsoon seasons, suggesting better productivity level during pre-monsoon, followed by SW monsoon, but the least during the post-monsoon. All the seasons, however, indicated a mesotrophic condition in the estuary and the assimilative capacity of the estuary is found to be in good to fairly good state (pre-monsoon < SW monsoon < post-monsoon).

Visual plumes coastal dispersion modeling in south-west Sabah

The visual plumes model encompassing the DKHW (Davis, Kannberg, Hirst model for Windows) and Update Merge (UM3) sub-models were utilized in the modeling exercise. In theory, the dilution capacity of open waters, particularly coastal areas, straits and oceans are enormous. This means that for surface and sub-merged point source discharges, the effluent concentration (C e ) will cause insignificant change in the overall ambient water quality. Instead, C e will eventually reach C a (ambient concentration) over a spatial distance (vertical and horizontal). This distance is of interest with regards to water quality preservation efforts as the macro level distribution effects of the pollutant species in question can be determined. The travel distance (l t ) is a main function of ambient current velocity (m/s) and direction. Prior to the modeling exercise, field data pertaining to ambient water quality, hydraulic characteristics and tide patterns were collected. The modeling results indicated that there was no significant change in ambient concentration for all constituents modeled when the effluent discharge was increased from 1,500 m 3 /h to 2,400 m 3 /h, as long as the current quality was maintained. The plume travel distance would also not entrain into foreign waters as long as proposed volumetric discharge rate is no violated. Key words : Visual plumes, coastal, Sabah.