Groyne system modification is described related to restoration efforts to Koggaia lagoon, Sri Lanka.The large-scale unplanned sand removal at the lagoon mouth shifted the formation of sand bar towards the lagoon and m...Groyne system modification is described related to restoration efforts to Koggaia lagoon, Sri Lanka.The large-scale unplanned sand removal at the lagoon mouth shifted the formation of sand bar towards the lagoon and made adverse effects on its ecosystem. After the removal of the natural sand bar, groyne system was constructed to avoid sand deposition in the lagoon and to protect the highway bridge （across the lagoon outlet channel） from the wave attack. The existing groyne system resulted the lagoon mouth being permanently open to sea which in turn led to many environmental problems. Groyne system modification is proposed in this study to reduce the sea water intrusion.Water budget and two-dimensional depth averaged hydrodynamic model were developed for understanding the hydrologic and flow characteristics of the lagoon. Numerical experiments was performed at lagoon mouth area for two cases： （1） existing condition and （2） proposed rubble mound groyne system condition. Comparison of results was obtained for both cases to describe flow pattern at lagoon mouth. Results further showed, the width should be reduced to a maximum of 40 m. Proposed mouth width （40 m） pushed the salting factor towards 0.5 from 0.68. Salting factor reduction with the groyne modification may result a predominant influence of fresh water which may in turn lead lagoon to a fresh water ecosystem.展开更多
The imposition and lifting of non-pharmaceutical interventions(NPIs)to avert the COVID-19 pandemic have gained popularity worldwide and will continue to be enforced until herd immunity is achieved.We developed a linea...The imposition and lifting of non-pharmaceutical interventions(NPIs)to avert the COVID-19 pandemic have gained popularity worldwide and will continue to be enforced until herd immunity is achieved.We developed a linear regression model to ascertain the nexus between the time-varying reproduction number averaged over a time window of six days(R_(ts))and seven NPIs:contact tracing,quarantine efforts,social distancing and health checks,hand hygiene,wearing of facemasks,lockdown and isolation,and health-related supports.Our analysis suggests that the second wave that emerged in Sri Lanka in early October 2020 continued despite numerous NPIs.The model indicates that the most effective single NPI was lockdown and isolation.Conversely,the least effective individual NPIs were hand hygiene and wearing of facemasks.The model also demonstrates that to mitigate the second wave to a satisfactory level(R_(ts)<1),the best single NPI was the contact tracing with stringent imposition(%of improvement of R_(ts) was 69.43 against the base case).By contrast,the best combination of two NPIs was the lockdown&isolation with health-related supports(%of improvement was 31.92 against the base case).As such,many health authorities worldwide can use this model to successfully strategize the imposition and lifting of NPIs for averting the COVID-19 pandemic.展开更多
文摘Groyne system modification is described related to restoration efforts to Koggaia lagoon, Sri Lanka.The large-scale unplanned sand removal at the lagoon mouth shifted the formation of sand bar towards the lagoon and made adverse effects on its ecosystem. After the removal of the natural sand bar, groyne system was constructed to avoid sand deposition in the lagoon and to protect the highway bridge （across the lagoon outlet channel） from the wave attack. The existing groyne system resulted the lagoon mouth being permanently open to sea which in turn led to many environmental problems. Groyne system modification is proposed in this study to reduce the sea water intrusion.Water budget and two-dimensional depth averaged hydrodynamic model were developed for understanding the hydrologic and flow characteristics of the lagoon. Numerical experiments was performed at lagoon mouth area for two cases： （1） existing condition and （2） proposed rubble mound groyne system condition. Comparison of results was obtained for both cases to describe flow pattern at lagoon mouth. Results further showed, the width should be reduced to a maximum of 40 m. Proposed mouth width （40 m） pushed the salting factor towards 0.5 from 0.68. Salting factor reduction with the groyne modification may result a predominant influence of fresh water which may in turn lead lagoon to a fresh water ecosystem.
文摘The imposition and lifting of non-pharmaceutical interventions(NPIs)to avert the COVID-19 pandemic have gained popularity worldwide and will continue to be enforced until herd immunity is achieved.We developed a linear regression model to ascertain the nexus between the time-varying reproduction number averaged over a time window of six days(R_(ts))and seven NPIs:contact tracing,quarantine efforts,social distancing and health checks,hand hygiene,wearing of facemasks,lockdown and isolation,and health-related supports.Our analysis suggests that the second wave that emerged in Sri Lanka in early October 2020 continued despite numerous NPIs.The model indicates that the most effective single NPI was lockdown and isolation.Conversely,the least effective individual NPIs were hand hygiene and wearing of facemasks.The model also demonstrates that to mitigate the second wave to a satisfactory level(R_(ts)<1),the best single NPI was the contact tracing with stringent imposition(%of improvement of R_(ts) was 69.43 against the base case).By contrast,the best combination of two NPIs was the lockdown&isolation with health-related supports(%of improvement was 31.92 against the base case).As such,many health authorities worldwide can use this model to successfully strategize the imposition and lifting of NPIs for averting the COVID-19 pandemic.
