Environmental monitoring and assessment, Jan 19, 2017
Water quality of the Kelani River has become a critical issue in Sri Lanka due to the high cost o... more Water quality of the Kelani River has become a critical issue in Sri Lanka due to the high cost of maintaining drinking water standards and the market and non-market costs of deteriorating river ecosystem services. By integrating a catchment model with a river model of water quality, we developed a method to estimate the effect of pollution sources on ambient water quality. Using integrated model simulations, we estimate (1) the relative contribution from point (industrial and domestic) and non-point sources (river catchment) to river water quality and (2) pollutant transfer coefficients for zones along the lower section of the river. Transfer coefficients provide the basis for policy analyses in relation to the location of new industries and the setting of priorities for industrial pollution control. They also offer valuable information to design socially optimal economic policy to manage industrialized river catchments.
Regularly observed seiches from tide gauge records around the Sri Lanka coast have been analyzed ... more Regularly observed seiches from tide gauge records around the Sri Lanka coast have been analyzed to determine the forcing mechanisms. The seiche periods range from a few 10s of min to 2 h. Fortnightly and seasonal variations of seiche amplitudes are clearly visible on the east coast. These seiche amplitudes are particularly large approximately 6-8 days after spring tides, with maximum seiche amplitudes observed during March-April and October-November, suggesting that the seiche variation could be related to stratification and internal wave activity. There is no visible fortnightly and seasonal variation of seiche amplitudes in west coast records. Instead, they show a daily pattern with relatively larger seiches around 1000 LT, suggesting that the seiches on the west coast could result from diurnal atmospheric forcing. Barotropic and two-layer models have been developed to investigate the influence of atmospheric forcing and internal wave activity on the seiches. A barotropic model applied to the west coast shows that the daily seiche amplitude variation could be simulated with cyclic diurnal meteorological forcing. Two-layer model runs for Trincomalee Bay and the adjacent east coast shelf suggest that seiche amplitudes are proportional to vertical stratification and mixed layer depths. Therefore, the observed seiches there could be excited by internal waves, which originate as far away as the Andaman Sea during spring tides and have a travel time of 6-8 days to the Sri Lankan east coast. However, further studies, including direct measurements of internal wave activity within the region, are required to confirm this hypothesis.
Sea level oscillations at the Buenos Aires province coastal waters were detected as a response to... more Sea level oscillations at the Buenos Aires province coastal waters were detected as a response to the magnitude 9.3 earthquake centered off the west coast of northern Sumatra (3.3071N, 95.9471E) on December 26, 2004 at 00:59 UTC. The aim of the present work is to report the first description on sea level oscillations in the Buenos Aires continental shelf generated by oceanic seismic activity. Sea level records gathered at three tide gauge stations located at Santa Teresita (361 32 0 S, 561 40 0 W), Mar del Plata (381 05 0 S, 571 30 0 W) and Puerto Belgrano (381 54 0 S, 621 06 0 W) were filtered and analyzed. The first arrival was measured at Mar del Plata (December 27, 2004, 00:15 UTC). At Santa Teresita and Puerto Belgrano, the tsunami reached the coast 33 min and 4.5 h later than at Mar del Plata, respectively. Maximum wave heights observed were 0.27, 0.15 and 0.20 m at Santa Teresita, Mar del Plata and Puerto Belgrano stations, respectively, and wave periods were detected in the range from 20 to 120 min. Wave amplitudes presented a remarkable temporal variability in the period immediately following tsunami wave arrival. After the first arrivals, waves lasted during the first 40 and 54 h at Mar del Plata and Santa Teresita, respectively. Even though, atmospherically forced sea level oscillations (in the tsunami frequency band) are frequently observed at different tide stations at locations on the Buenos Aires province coast, the weather patterns between December 24 and 27, 2004 showed no evidences of either frontal passages or atmospheric gravity waves. Thus sea level perturbations recorded at Santa Teresita, Mar del Plata and Puerto Belgrano stations can certainly be linked to the Indian Ocean tsunami.
Plastic debris is the most common and exponentially increasing human pollutant in the world's oce... more Plastic debris is the most common and exponentially increasing human pollutant in the world's ocean. The distribution and impact of plastic in the Pacific and Atlantic oceans have been the subject of many publications but not so the Indian Ocean (IO). Some of the IO rim countries have the highest population densities globally and mismanagement of plastic waste is of concern in many of these rim states. Some of the most plastic-polluted rivers empty into the IO, with all this suggesting that the IO receives a tremendous amount of plastic debris each year. However, the concentration, distribution, and impacts of plastics in the IO are poorly understood as the region is under-sampled compared to other oceans. In this review, we discuss sources and sinks, which are specific to the IO. We also discuss unique atmospheric, oceanographic, and topographic features of the IO that control plastic distribution, such as reversing wind directions due to the monsoon, fronts, and upwelling regions. We identify hotspots of possible plastic accumulation in the IO, which differ between the two hemispheres. In the southern IO, plastics accumulate in a garbage patch in the subtropical gyre. However, this garbage patch is not well defined, and plastics may leak into the southern Atlantic or the Pacific Ocean. There is no subtropical gyre and associated garbage in the northern IO due to the presence of landmasses. Instead, the majority of buoyant plastics most likely end up on coastlines. Finally, we identify the vast knowledge gaps concerning plastics in the IO and point to the most pressing topics for future investigation.
Malaysia Airlines flight MH370, with 239 passengers on board, was scheduled to fly from the Malay... more Malaysia Airlines flight MH370, with 239 passengers on board, was scheduled to fly from the Malaysian capital, Kuala Lumpur, to Beijing in China on Saturday 8 March 2014. It disappeared from civilian radar screens about an hour into the scheduled six-hour flight. Initially the search region was in the south China Sea, but on 24 March, it was revealed that satellite data from Inmarsat indicated that the plane flew along the southern search corridor and the flight "ended in the southern Indian Ocean". Initially the search area was in the Southern Ocean sector of the Indian Ocean (86–90 o E 44–46 o S). Further analysis of the Inmarsat data indicated the flight might have crashed ~1000 km to the north of the Southern Ocean site (94-98 o E 27-34 o S). Subsequently, the search site was moved farther north to the vicinity of the Wallaby Plateau (103-104 o E 20-21 o S). There was a huge demand by the media on how oceanography could help with the search, and the modelling group at ...
Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, wit... more Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, with the Arabian Sea on its western side and the Bay of Bengal on its eastern side, and experiences biannually reversing monsoon winds. Aggregations of blue whale (Balaenoptera musculus) have been observed along the southern coast of Sri Lanka during the northeast (NE) monsoon, when satellite imagery indicates lower productivity in the surface waters. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The model was run for 3 years to examine the seasonal and shorter-term (∼ 10 days) variability. The results reproduced correctly the reversing current system, between the Equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the southwest (SW) monsoon transporting 11.5 Sv (mean over 2010-2012) and the westward flowing Northeast Monsoon Current (NMC) transporting 9.6 Sv during the NE monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the southern coast. During the SW monsoon, the island deflects the eastward flowing SMC southward, whilst along the eastern coast, the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the southern coast, resulting from southward flow converging along the southern coast and subsequent divergence associated with the offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind-driven flow along the eastern and western coasts: during the SW (NE) monsoon, the flow along the western (eastern) coast was stronger, migrating the upwelling centre to the east (west).
Tide gauge data were used to identify the occurrence, characteristics, and cause of tsunamis of m... more Tide gauge data were used to identify the occurrence, characteristics, and cause of tsunamis of meteorological origin (termed 'meteotsunamis') along the Western Australian coast. This is the first study to identify meteotsunamis in this region, and the results indicated that they occur frequently. Although meteotsunamis are not catastrophic to the extent of major seismically induced basin-scale events, the wave heights of meteotsunamis examined at some local stations in this study were higher than those recorded through seismic tsunamis. In June 2012, a meteotsunami contributed to an extreme water-level event at Fremantle, which recorded the highest water level in over 115 years. Meteotsunamis (wave heights [0.4 m, when the mean tidal range in the region is *0.5 m) were found to coincide with thunderstorms in summer and the passage of low-pressure systems during winter. Spectral analysis of tide gauge time series records showed that existing continental seiche oscillations (periods between 30 min and 5 h) were enhanced during the meteotsunamis, with a high proportion of energy transferred to the continental shelf oscillation period. Three recent meteotsunami events (22 March 2010, 10 June 2012, and 7 January 2013) two due to summer thunderstorms and one due to a winter frontal system were chosen for detailed analysis. The meteotsunami amplitudes were up to a factor 2 larger than the local tidal range and sometimes contributed up to 85 % of the non-tidal water signal. A single meteorological event was found to generate several meteotsunamis along the coast, up to 500 km apart, as the air pressure disturbance propagated over the continental shelf; however, the topography and local bathymetry of the continental shelf defined the local sea-level resonance characteristics at each location. With the available data (sea level and meteorological), the exact mechanisms for the generation of the meteotsunamis could not be isolated.
Analysis of multi-year current meter data across North West shelf of Australia identified various... more Analysis of multi-year current meter data across North West shelf of Australia identified various aspects of the mean flow in a macro-tidal environment. Main features of the flow appear to be a continuous alongshore south-westward flow, i.e., Holloway current located along the continental shelf edge in depth 100-200 m. Annually, the current transports ~ 1 Sv of lower salinity, higher temperature water from the tropical regions to North West Cape. The Holloway current is at its maximum intensity (up to 2 Sv) during autumn/winter (Apr-Jul) when the winds are either weak or the region is dominated by southeast trade winds. Unlike alongshore flow, cross-shore structure of the flow is fairly complex and shows variations with depth and season. A new mechanism is proposed to justify the observed intensification of the flow in austral autumn that is closely related to the seasonal cycle of sea level around Australia. Each year, due to the monsoon cycles there is a high sea level anomaly that peaks in February in the Gulf of Carpentaria in the upstream side of the Holloway current that manifests itself as southward progressive high sea level anomalies in the following months along the West Australian coastline. Observed onshore fluxes can also have some implications for the strength of the Holloway current.
Meteotsunamis are generated by meteorological events, particularly moving pressure disturbances d... more Meteotsunamis are generated by meteorological events, particularly moving pressure disturbances due to squalls, thunderstorms, frontal passages and atmospheric gravity waves. Relatively small initial sea-level perturbations, of the order of a few centimetres, can increase significantly through multiresonant phenomena to create destructive events through the superposition of different factors. The global occurrence of meteotsunamis and the different resonance phenomena leading to amplification of meteotsunamis are reviewed. Results from idealized numerical modelling and field measurements from southwest Australia are presented to highlight the relative importance of the different processes. It is shown that the main influence that leads to amplification of the initial disturbance is due to wave shoaling and topographic resonance. Although meteotsunamis are not catastrophic to the extent of major seismically induced basin-scale events, the temporal and spatial occurrence of meteotsunamis are higher than those of seismic tsunamis as the atmospheric disturbances responsible for the generation of meteotsunamis are more common. High-energy events occur only for very specific combinations of resonant effects. The rareness of such combinations is perhaps the main reason why destructive meteotsunamis are exceptional and observed only at a limited number of sites globally.
Meteotsunamis are generated by meteorological events, particularly moving pressure disturbances d... more Meteotsunamis are generated by meteorological events, particularly moving pressure disturbances due to squalls, thunderstorms, frontal passages and atmospheric gravity waves. Relatively small initial sea-level perturbations, of the order of a few centimetres, can increase significantly through multiresonant phenomena to create destructive events through the superposition of different factors. The global occurrence of meteotsunamis and the different resonance phenomena leading to amplification of meteotsunamis are reviewed. Results from idealized numerical modelling and field measurements from southwest Australia are presented to highlight the relative importance of the different processes. It is shown that the main influence that leads to amplification of the initial disturbance is due to wave shoaling and topographic resonance. Although meteotsunamis are not catastrophic to the extent of major seismically induced basin-scale events, the temporal and spatial occurrence of meteotsuna...
... The Vega radar gauge is also a suitable solution since it lends itself to quick and simple in... more ... The Vega radar gauge is also a suitable solution since it lends itself to quick and simple installation due to the small physical size, light weight and low power requirements. Page 21 Page 23. ... Baptista, MA, S. Heitor, JM Miranda, PMA Miranda and L. Mendes Victor (1998). ...
The occurrence of extreme water level events along low-lying, highly populated and/or developed c... more The occurrence of extreme water level events along low-lying, highly populated and/or developed coastlines can lead to devastating impacts on coastal infrastructure. Therefore it is very important that the probabilities of extreme water levels are accurately evaluated to inform flood and coastal management and for future planning. The aim of this study was to provide estimates of present day extreme total water level exceedance probabilities around the whole coastline of Australia, arising from combinations of mean sea level, astronomical tide and storm surges generated by both extra-tropical and tropical storms, but exclusive of surface gravity waves. The study has been undertaken in two main stages. In the first stage, a high-resolution (~10 km along the coast) hydrodynamic depth averaged model has been configured for the whole coastline of Australia using the Danish Hydraulics Institute’s Mike21 modelling suite of tools. The model has been forced with astronomical tidal levels, d...
ABSTRACT Wandres, M., Pattiaratchi, C., Wijeratne, E.M.S., Hetzel, Y., 2016. The influence of the... more ABSTRACT Wandres, M., Pattiaratchi, C., Wijeratne, E.M.S., Hetzel, Y., 2016. The influence of the subtropical high-pressure ridge on the Western Australian wave climate. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 567–571. Coconut Creek (Florida), ISSN 0749-0208. Understanding the wave climate of a region is critical for its coastal zone management. The southwest Western Australian (SWWA) wave climate is dominated by waves generated in the energetic and variable Southern Ocean (SO) storm belt. The latitudinal variability of the SO storm belt can be described by the position (latitude) of the subtropical high-pressure ridge (STRP). To gain an understanding in how the SO storm belt influences the SWWA wave climate, the relationship between the STRP and the waves was examined. Wave data from three directional wave buoys along the SWWA shelf were compared to the STRP. The seasonal and interannual variability of the STRP and the wave climate indicated a significant correlation between the STRP and the SWWA wave heights with the strongest relationship during winter. A northward shift of the STRP resulted in a northward shift of the SO storm belt which led to increased wave heights in SWWA whereas a southward shift of the STRP resulted in decreased wave heights. The close relationship between the STRP and the local wave climate, suggests it could be used to estimate future wave climates in SWWA.
Short-period sea level changes around the islands of Mauritius and Rodrigues in thecentral Indian... more Short-period sea level changes around the islands of Mauritius and Rodrigues in thecentral Indian Ocean have been analysed to determine the favoured seiche periods. The largestamplitudes are found inside the harbours of Port Louis, Mauritius (7 and 20 minutes) and PortMathurin, Rodrigues (25 minutes), but these amplitudes are much smaller just outside the harbours,and the characteristic periods are found only locally, confirming that local topography controlsthe periods of the seiching. The extent and energising of these seiching phenomena calls forfurther investigation. Associated seiche currents, potentially much stronger than tidal currents,could influence harbour shipping movements. Analysis of the sea level data showed that there aresignificant spatial variations in the amplitudes and phases of the tides around Mauritius Island,but the around-island tidal variations are much smaller for Rodrigues Island.
Western Indian Ocean Journal of Marine Science, 2009
Mean sea level (MSL) data recorded at tide gauge stations in Sri Lanka and southern India, some p... more Mean sea level (MSL) data recorded at tide gauge stations in Sri Lanka and southern India, some previously unpublished, have been used in order to determine the main characteristics of the seasonal cycle of MSL in the region, concentrating on the annual component. Altimetric, meteorological and hydrographic information, together with results from numerical modelling, have been employed to try to understand the main factors which contribute to the observed MSL changes. Success in obtaining understanding has been relatively modest, especially for the southern Indian coastline, but proposals are put forward for further work in order to derive greater insight into the seasonal variability. With regard to Sri Lanka, it is evident that change in steric sea level (or dynamic height) is the main factor leading to seasonal MSL change. However, even in this case, there are apparent systematic differences between the various data sets, indicating scope for further research.
Industrialization and urbanization, as a result of rapid economic development, have led to the de... more Industrialization and urbanization, as a result of rapid economic development, have led to the deterioration of water quality in many rivers in developing countries. The Kelani River in Sri Lanka provides drinking water to Colombo and a range of market and non-market ecosystem services; but these services are threatened by deteriorating water quality. We apply a hydro-economic model that accounts for spatial patterns of water quality and abatement cost variability between firms in the catchment. The hydro-economic model combines a hydrological model of water quality with an economic optimization model to determine a cost-effective policy under alternate policy regimes. These include: the existing policy based on effluent concentration standards, effluent trading and effluent trading with multiple zones and an effluent tax. Tradeable permits with multiple zones are the least cost policy option that accounts for both spatial externalities and abatement costs. However, given current institutional capabilities, an effluent tax would be a more realistic second best policy as a transition from the current policy of effluent concentration standards to a policy based on the quantity of effluents.
Environmental monitoring and assessment, Jan 19, 2017
Water quality of the Kelani River has become a critical issue in Sri Lanka due to the high cost o... more Water quality of the Kelani River has become a critical issue in Sri Lanka due to the high cost of maintaining drinking water standards and the market and non-market costs of deteriorating river ecosystem services. By integrating a catchment model with a river model of water quality, we developed a method to estimate the effect of pollution sources on ambient water quality. Using integrated model simulations, we estimate (1) the relative contribution from point (industrial and domestic) and non-point sources (river catchment) to river water quality and (2) pollutant transfer coefficients for zones along the lower section of the river. Transfer coefficients provide the basis for policy analyses in relation to the location of new industries and the setting of priorities for industrial pollution control. They also offer valuable information to design socially optimal economic policy to manage industrialized river catchments.
Regularly observed seiches from tide gauge records around the Sri Lanka coast have been analyzed ... more Regularly observed seiches from tide gauge records around the Sri Lanka coast have been analyzed to determine the forcing mechanisms. The seiche periods range from a few 10s of min to 2 h. Fortnightly and seasonal variations of seiche amplitudes are clearly visible on the east coast. These seiche amplitudes are particularly large approximately 6-8 days after spring tides, with maximum seiche amplitudes observed during March-April and October-November, suggesting that the seiche variation could be related to stratification and internal wave activity. There is no visible fortnightly and seasonal variation of seiche amplitudes in west coast records. Instead, they show a daily pattern with relatively larger seiches around 1000 LT, suggesting that the seiches on the west coast could result from diurnal atmospheric forcing. Barotropic and two-layer models have been developed to investigate the influence of atmospheric forcing and internal wave activity on the seiches. A barotropic model applied to the west coast shows that the daily seiche amplitude variation could be simulated with cyclic diurnal meteorological forcing. Two-layer model runs for Trincomalee Bay and the adjacent east coast shelf suggest that seiche amplitudes are proportional to vertical stratification and mixed layer depths. Therefore, the observed seiches there could be excited by internal waves, which originate as far away as the Andaman Sea during spring tides and have a travel time of 6-8 days to the Sri Lankan east coast. However, further studies, including direct measurements of internal wave activity within the region, are required to confirm this hypothesis.
Sea level oscillations at the Buenos Aires province coastal waters were detected as a response to... more Sea level oscillations at the Buenos Aires province coastal waters were detected as a response to the magnitude 9.3 earthquake centered off the west coast of northern Sumatra (3.3071N, 95.9471E) on December 26, 2004 at 00:59 UTC. The aim of the present work is to report the first description on sea level oscillations in the Buenos Aires continental shelf generated by oceanic seismic activity. Sea level records gathered at three tide gauge stations located at Santa Teresita (361 32 0 S, 561 40 0 W), Mar del Plata (381 05 0 S, 571 30 0 W) and Puerto Belgrano (381 54 0 S, 621 06 0 W) were filtered and analyzed. The first arrival was measured at Mar del Plata (December 27, 2004, 00:15 UTC). At Santa Teresita and Puerto Belgrano, the tsunami reached the coast 33 min and 4.5 h later than at Mar del Plata, respectively. Maximum wave heights observed were 0.27, 0.15 and 0.20 m at Santa Teresita, Mar del Plata and Puerto Belgrano stations, respectively, and wave periods were detected in the range from 20 to 120 min. Wave amplitudes presented a remarkable temporal variability in the period immediately following tsunami wave arrival. After the first arrivals, waves lasted during the first 40 and 54 h at Mar del Plata and Santa Teresita, respectively. Even though, atmospherically forced sea level oscillations (in the tsunami frequency band) are frequently observed at different tide stations at locations on the Buenos Aires province coast, the weather patterns between December 24 and 27, 2004 showed no evidences of either frontal passages or atmospheric gravity waves. Thus sea level perturbations recorded at Santa Teresita, Mar del Plata and Puerto Belgrano stations can certainly be linked to the Indian Ocean tsunami.
Plastic debris is the most common and exponentially increasing human pollutant in the world's oce... more Plastic debris is the most common and exponentially increasing human pollutant in the world's ocean. The distribution and impact of plastic in the Pacific and Atlantic oceans have been the subject of many publications but not so the Indian Ocean (IO). Some of the IO rim countries have the highest population densities globally and mismanagement of plastic waste is of concern in many of these rim states. Some of the most plastic-polluted rivers empty into the IO, with all this suggesting that the IO receives a tremendous amount of plastic debris each year. However, the concentration, distribution, and impacts of plastics in the IO are poorly understood as the region is under-sampled compared to other oceans. In this review, we discuss sources and sinks, which are specific to the IO. We also discuss unique atmospheric, oceanographic, and topographic features of the IO that control plastic distribution, such as reversing wind directions due to the monsoon, fronts, and upwelling regions. We identify hotspots of possible plastic accumulation in the IO, which differ between the two hemispheres. In the southern IO, plastics accumulate in a garbage patch in the subtropical gyre. However, this garbage patch is not well defined, and plastics may leak into the southern Atlantic or the Pacific Ocean. There is no subtropical gyre and associated garbage in the northern IO due to the presence of landmasses. Instead, the majority of buoyant plastics most likely end up on coastlines. Finally, we identify the vast knowledge gaps concerning plastics in the IO and point to the most pressing topics for future investigation.
Malaysia Airlines flight MH370, with 239 passengers on board, was scheduled to fly from the Malay... more Malaysia Airlines flight MH370, with 239 passengers on board, was scheduled to fly from the Malaysian capital, Kuala Lumpur, to Beijing in China on Saturday 8 March 2014. It disappeared from civilian radar screens about an hour into the scheduled six-hour flight. Initially the search region was in the south China Sea, but on 24 March, it was revealed that satellite data from Inmarsat indicated that the plane flew along the southern search corridor and the flight "ended in the southern Indian Ocean". Initially the search area was in the Southern Ocean sector of the Indian Ocean (86–90 o E 44–46 o S). Further analysis of the Inmarsat data indicated the flight might have crashed ~1000 km to the north of the Southern Ocean site (94-98 o E 27-34 o S). Subsequently, the search site was moved farther north to the vicinity of the Wallaby Plateau (103-104 o E 20-21 o S). There was a huge demand by the media on how oceanography could help with the search, and the modelling group at ...
Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, wit... more Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, with the Arabian Sea on its western side and the Bay of Bengal on its eastern side, and experiences biannually reversing monsoon winds. Aggregations of blue whale (Balaenoptera musculus) have been observed along the southern coast of Sri Lanka during the northeast (NE) monsoon, when satellite imagery indicates lower productivity in the surface waters. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The model was run for 3 years to examine the seasonal and shorter-term (∼ 10 days) variability. The results reproduced correctly the reversing current system, between the Equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the southwest (SW) monsoon transporting 11.5 Sv (mean over 2010-2012) and the westward flowing Northeast Monsoon Current (NMC) transporting 9.6 Sv during the NE monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the southern coast. During the SW monsoon, the island deflects the eastward flowing SMC southward, whilst along the eastern coast, the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the southern coast, resulting from southward flow converging along the southern coast and subsequent divergence associated with the offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind-driven flow along the eastern and western coasts: during the SW (NE) monsoon, the flow along the western (eastern) coast was stronger, migrating the upwelling centre to the east (west).
Tide gauge data were used to identify the occurrence, characteristics, and cause of tsunamis of m... more Tide gauge data were used to identify the occurrence, characteristics, and cause of tsunamis of meteorological origin (termed 'meteotsunamis') along the Western Australian coast. This is the first study to identify meteotsunamis in this region, and the results indicated that they occur frequently. Although meteotsunamis are not catastrophic to the extent of major seismically induced basin-scale events, the wave heights of meteotsunamis examined at some local stations in this study were higher than those recorded through seismic tsunamis. In June 2012, a meteotsunami contributed to an extreme water-level event at Fremantle, which recorded the highest water level in over 115 years. Meteotsunamis (wave heights [0.4 m, when the mean tidal range in the region is *0.5 m) were found to coincide with thunderstorms in summer and the passage of low-pressure systems during winter. Spectral analysis of tide gauge time series records showed that existing continental seiche oscillations (periods between 30 min and 5 h) were enhanced during the meteotsunamis, with a high proportion of energy transferred to the continental shelf oscillation period. Three recent meteotsunami events (22 March 2010, 10 June 2012, and 7 January 2013) two due to summer thunderstorms and one due to a winter frontal system were chosen for detailed analysis. The meteotsunami amplitudes were up to a factor 2 larger than the local tidal range and sometimes contributed up to 85 % of the non-tidal water signal. A single meteorological event was found to generate several meteotsunamis along the coast, up to 500 km apart, as the air pressure disturbance propagated over the continental shelf; however, the topography and local bathymetry of the continental shelf defined the local sea-level resonance characteristics at each location. With the available data (sea level and meteorological), the exact mechanisms for the generation of the meteotsunamis could not be isolated.
Analysis of multi-year current meter data across North West shelf of Australia identified various... more Analysis of multi-year current meter data across North West shelf of Australia identified various aspects of the mean flow in a macro-tidal environment. Main features of the flow appear to be a continuous alongshore south-westward flow, i.e., Holloway current located along the continental shelf edge in depth 100-200 m. Annually, the current transports ~ 1 Sv of lower salinity, higher temperature water from the tropical regions to North West Cape. The Holloway current is at its maximum intensity (up to 2 Sv) during autumn/winter (Apr-Jul) when the winds are either weak or the region is dominated by southeast trade winds. Unlike alongshore flow, cross-shore structure of the flow is fairly complex and shows variations with depth and season. A new mechanism is proposed to justify the observed intensification of the flow in austral autumn that is closely related to the seasonal cycle of sea level around Australia. Each year, due to the monsoon cycles there is a high sea level anomaly that peaks in February in the Gulf of Carpentaria in the upstream side of the Holloway current that manifests itself as southward progressive high sea level anomalies in the following months along the West Australian coastline. Observed onshore fluxes can also have some implications for the strength of the Holloway current.
Meteotsunamis are generated by meteorological events, particularly moving pressure disturbances d... more Meteotsunamis are generated by meteorological events, particularly moving pressure disturbances due to squalls, thunderstorms, frontal passages and atmospheric gravity waves. Relatively small initial sea-level perturbations, of the order of a few centimetres, can increase significantly through multiresonant phenomena to create destructive events through the superposition of different factors. The global occurrence of meteotsunamis and the different resonance phenomena leading to amplification of meteotsunamis are reviewed. Results from idealized numerical modelling and field measurements from southwest Australia are presented to highlight the relative importance of the different processes. It is shown that the main influence that leads to amplification of the initial disturbance is due to wave shoaling and topographic resonance. Although meteotsunamis are not catastrophic to the extent of major seismically induced basin-scale events, the temporal and spatial occurrence of meteotsunamis are higher than those of seismic tsunamis as the atmospheric disturbances responsible for the generation of meteotsunamis are more common. High-energy events occur only for very specific combinations of resonant effects. The rareness of such combinations is perhaps the main reason why destructive meteotsunamis are exceptional and observed only at a limited number of sites globally.
Meteotsunamis are generated by meteorological events, particularly moving pressure disturbances d... more Meteotsunamis are generated by meteorological events, particularly moving pressure disturbances due to squalls, thunderstorms, frontal passages and atmospheric gravity waves. Relatively small initial sea-level perturbations, of the order of a few centimetres, can increase significantly through multiresonant phenomena to create destructive events through the superposition of different factors. The global occurrence of meteotsunamis and the different resonance phenomena leading to amplification of meteotsunamis are reviewed. Results from idealized numerical modelling and field measurements from southwest Australia are presented to highlight the relative importance of the different processes. It is shown that the main influence that leads to amplification of the initial disturbance is due to wave shoaling and topographic resonance. Although meteotsunamis are not catastrophic to the extent of major seismically induced basin-scale events, the temporal and spatial occurrence of meteotsuna...
... The Vega radar gauge is also a suitable solution since it lends itself to quick and simple in... more ... The Vega radar gauge is also a suitable solution since it lends itself to quick and simple installation due to the small physical size, light weight and low power requirements. Page 21 Page 23. ... Baptista, MA, S. Heitor, JM Miranda, PMA Miranda and L. Mendes Victor (1998). ...
The occurrence of extreme water level events along low-lying, highly populated and/or developed c... more The occurrence of extreme water level events along low-lying, highly populated and/or developed coastlines can lead to devastating impacts on coastal infrastructure. Therefore it is very important that the probabilities of extreme water levels are accurately evaluated to inform flood and coastal management and for future planning. The aim of this study was to provide estimates of present day extreme total water level exceedance probabilities around the whole coastline of Australia, arising from combinations of mean sea level, astronomical tide and storm surges generated by both extra-tropical and tropical storms, but exclusive of surface gravity waves. The study has been undertaken in two main stages. In the first stage, a high-resolution (~10 km along the coast) hydrodynamic depth averaged model has been configured for the whole coastline of Australia using the Danish Hydraulics Institute’s Mike21 modelling suite of tools. The model has been forced with astronomical tidal levels, d...
ABSTRACT Wandres, M., Pattiaratchi, C., Wijeratne, E.M.S., Hetzel, Y., 2016. The influence of the... more ABSTRACT Wandres, M., Pattiaratchi, C., Wijeratne, E.M.S., Hetzel, Y., 2016. The influence of the subtropical high-pressure ridge on the Western Australian wave climate. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 567–571. Coconut Creek (Florida), ISSN 0749-0208. Understanding the wave climate of a region is critical for its coastal zone management. The southwest Western Australian (SWWA) wave climate is dominated by waves generated in the energetic and variable Southern Ocean (SO) storm belt. The latitudinal variability of the SO storm belt can be described by the position (latitude) of the subtropical high-pressure ridge (STRP). To gain an understanding in how the SO storm belt influences the SWWA wave climate, the relationship between the STRP and the waves was examined. Wave data from three directional wave buoys along the SWWA shelf were compared to the STRP. The seasonal and interannual variability of the STRP and the wave climate indicated a significant correlation between the STRP and the SWWA wave heights with the strongest relationship during winter. A northward shift of the STRP resulted in a northward shift of the SO storm belt which led to increased wave heights in SWWA whereas a southward shift of the STRP resulted in decreased wave heights. The close relationship between the STRP and the local wave climate, suggests it could be used to estimate future wave climates in SWWA.
Short-period sea level changes around the islands of Mauritius and Rodrigues in thecentral Indian... more Short-period sea level changes around the islands of Mauritius and Rodrigues in thecentral Indian Ocean have been analysed to determine the favoured seiche periods. The largestamplitudes are found inside the harbours of Port Louis, Mauritius (7 and 20 minutes) and PortMathurin, Rodrigues (25 minutes), but these amplitudes are much smaller just outside the harbours,and the characteristic periods are found only locally, confirming that local topography controlsthe periods of the seiching. The extent and energising of these seiching phenomena calls forfurther investigation. Associated seiche currents, potentially much stronger than tidal currents,could influence harbour shipping movements. Analysis of the sea level data showed that there aresignificant spatial variations in the amplitudes and phases of the tides around Mauritius Island,but the around-island tidal variations are much smaller for Rodrigues Island.
Western Indian Ocean Journal of Marine Science, 2009
Mean sea level (MSL) data recorded at tide gauge stations in Sri Lanka and southern India, some p... more Mean sea level (MSL) data recorded at tide gauge stations in Sri Lanka and southern India, some previously unpublished, have been used in order to determine the main characteristics of the seasonal cycle of MSL in the region, concentrating on the annual component. Altimetric, meteorological and hydrographic information, together with results from numerical modelling, have been employed to try to understand the main factors which contribute to the observed MSL changes. Success in obtaining understanding has been relatively modest, especially for the southern Indian coastline, but proposals are put forward for further work in order to derive greater insight into the seasonal variability. With regard to Sri Lanka, it is evident that change in steric sea level (or dynamic height) is the main factor leading to seasonal MSL change. However, even in this case, there are apparent systematic differences between the various data sets, indicating scope for further research.
Industrialization and urbanization, as a result of rapid economic development, have led to the de... more Industrialization and urbanization, as a result of rapid economic development, have led to the deterioration of water quality in many rivers in developing countries. The Kelani River in Sri Lanka provides drinking water to Colombo and a range of market and non-market ecosystem services; but these services are threatened by deteriorating water quality. We apply a hydro-economic model that accounts for spatial patterns of water quality and abatement cost variability between firms in the catchment. The hydro-economic model combines a hydrological model of water quality with an economic optimization model to determine a cost-effective policy under alternate policy regimes. These include: the existing policy based on effluent concentration standards, effluent trading and effluent trading with multiple zones and an effluent tax. Tradeable permits with multiple zones are the least cost policy option that accounts for both spatial externalities and abatement costs. However, given current institutional capabilities, an effluent tax would be a more realistic second best policy as a transition from the current policy of effluent concentration standards to a policy based on the quantity of effluents.
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