Under climate change, sea-level rise and increasing storm surge intensity will increase the likel... more Under climate change, sea-level rise and increasing storm surge intensity will increase the likelihood of floods for low-lying coastal areas. Therefore, Coastal Flood Vulnerability Assessments (CFVA) are necessary to inform decision making for coastal management, where applicable. Two types of tools, hydrodynamic models and Geographic Information Systems (GIS), are commonly employed for these evaluations. Using Pigeon Point, Southwest Tobago, as a case study, this paper compares the application of both to determine the best approach for CFVA that can be used to guide coastal management. For hydrodynamic modelling, available and surveyed data on bathymetry, topography and tides along with current and future estimates of mean sea-level were used to create a structured and an unstructured grid model via the LISFLOOD-FP and TELEMAC-2D codes, respectively. For the GIS assessment, a coastal digital elevation model was developed using the same data on bathymetry and elevation. These models were used to project the present and future impact of storm surges on coastal flood extent at Pigeon Point. Outputs generated were compared and analysed within a GIS. Using predictions from TELEMAC-2D (full shallow water equations) as the baseline for comparison, average results acquired revealed that projections generated by all three models were consistent (less than 5.00% difference in flood predictions). To add certainty to the modelling results, all models were used to simulate an observed spring high tide event for model validation purposes. The Root Mean Squared Error (RMSE) was calculated as an indication of model performance. RMSE values indicated that all models were consistent and matched well to the field observations. However, further analysis revealed that inherent in the use of GIS for CFVA is hydraulic connectivity issues due to exclusion of flow dynamics, which leads to over-estimation in flood extent. Acknowledging the theory that over-estimation leads to over-management, it is suggested that hydrodynamic models are better suited for detailed CFVA, while GIS can be used rapidly as a potential indicator of flood exposure for large sites.
Jamaica, the third largest island in the Caribbean , has been affected significantly by flooding ... more Jamaica, the third largest island in the Caribbean , has been affected significantly by flooding and flood-related damage. Hence assessing the probability of flooding and susceptibility of a place to flood hazard has become a vital part of planning and development. In addition to heavy rainfall from tropical storms and Atlantic hurricanes, several terrestrial factors play significant roles in flooding, including local geology, geomorphology, hydrology and land-use. In this study, a GIS-based multi-criteria statistical methodology was developed to quantify hazard potential and to map flood characteristics. Fourteen factors potentially responsible for flooding were identified and used as initial input in a hybrid model that combined principal component analysis with logistic regression and frequency distribution analysis. Of these factors, seven explained 65 % of the variation in the data: elevation, slope angle, slope aspect, flow accumulation, a topographic wetness index, proximity to a stream network, and hydro-stratigraphic units. These were used to prepare the island's first map of flood hazard potential. Hazard potential was classified from very low to very high, nearly one-fifth (19.4 %) of the island was included within high or very high flood hazard zones. Further analysis revealed that areas prone to flooding are often low-lying and flat, or have shallow north-or northwest-facing slopes, are in close proximity to the stream network, and are situated on underlying impermeable lithology. The multi-criteria hybrid approach developed could classify 86.8 % of flood events correctly and produced a satisfactory validation result based on the receiver operating characteristic curve. The statistical method can be easily repeated and refined upon the availability of additional or higher quality data such as a high resolution digital elevation model. Additionally , the approach used in this study can be adopted to evaluate flood hazard in countries with similar characteristics , landscapes and climatic conditions, such as other Caribbean or Pacific Small Island Developing States.
Grande Riviere beach, located on the north coast of Trinidad, West Indies, is internationally rec... more Grande Riviere beach, located on the north coast of Trinidad, West Indies, is internationally recognised as a critical habitat/nesting ground for the endangered leatherback turtles (Dermochelys coriacea). Episodic extreme flooding of the Grande Riviere River led to the shifting of the river mouth and resulted in backshore beach erosion, with the most recent recorded event occurring in 2012. Following this event, the construction of a sand dam to arrest further erosion which threatened coastal infrastructure, precipitated a host of new problems ranging from beach instability to public health threats. In January 2013, high energy swell waves naturally in-filled the erosion channel, and the beach recovery continued over the successive months, thereby rendering the intervention in the previous year questionable. This paper presents a geomorphological analysis of beach dynamics for Grande Riviere, within the context of this erosion event. Data on beach profiles, sediment and coastal processes were collected using standard geomorphological techniques. Beach topographic analysis and water quality tests on impounded water in the erosion channel were conducted. Results indicate that the event created an erosion channel of 4843.42 m 3 over a contiguous area of 2794.25 m 2. While swell waves were able to naturally infill the channel, they also eroded 17,762 m 3 of sand overall across the beach. Water quality tests revealed that the impounded water was classified as a pollutant, and created challenges for remediation. Hydrologic and coastal geomorphologic interplay is responsible for the existence and sustainability of this coastal system. It is also evident that the beach system is able to recover naturally following extreme events. Our results demonstrate that effective and integrated management of such critical habitats remains dependent upon continuous monitoring data which should be used to inform policy and decision making.
This paper details research which compared rainfall data obtained from the Tropical Rainfall Meas... more This paper details research which compared rainfall data obtained from the Tropical Rainfall Measuring Mission [TRMM] to ground-based rain gauge data in northwestern Trinidad. Specifically, comparisons were made between the TRMM 3B42 (version 6) data product and rainfall data from rain gauges at the University Field Station and at the Sir Frank Stockdale building on the main campus of the University of the West Indies, St Augustine. The research was fo-cused on a TRMM grid cell which covers most of the Caroni River basin in Trini-dad. Comparisons between the data were made by using correlation tests. For each year during the analysis period 1998-2008, it was found that on a daily scale TRMM 3B42 data generally had a weak positive correlation (range of r values: 0.14-0.54) with the average rain gauge measurements. In addition, the TRMM satellite recorded fewer days per year of measured rainfall (an average of 124.1 days) as compared to rain gauges (an average of 180 days for both gauges). The average monthly rainfall measurements made by TRMM 3B42 data gave a clear representation of the differences between the dry and wet seasons in Trinidad. However, TRMM 3B42 still underestimated the rainfall measurements as compared to the rain gauge data.
The Leatherback turtle (Dermochelys coriacea) is a critically endangered species reliant on sandy... more The Leatherback turtle (Dermochelys coriacea) is a critically endangered species reliant on sandy beaches for nesting. Consequently, changes in beach morphology are a background factor in embryonic mortality. Grande Riviere beach has the highest density of nesting leatherbacks in the world, supporting a thriving ecotourist industry. The beach undergoes natural seasonal cycles of erosion and accretion, with renewal of sediment of importance to reduce diseases to eggs. Beach morphology surveys were conducted using standard surveying techniques both during and outside the nesting season, from the 2009 nesting season to the end of 2011. A survey was conducted in June 2012 to illustrate changes in the dynamics of the Grande Riviere River, and results reported here focus on a profile adjacent to the river. Relative stability was observed in the profile during the 2009 and 2011 nesting season, with 2010 displaying fluctuations in elevation throughout. In June 2012 there was a drastic decrease in estimated sediment volume of-644 m 3 due to the river changing to a westerly course.Nest loss was greatest when wave-induced erosion of beach sediment greater than 70cms in depth took place, or when river channels shifted, as in the 2012 nesting season. As stable river outlets are essential for both turtle nest preservation and the local fishing industry, the study has implications for the management of this sensitive environment.
The Surface Water and Ocean Topography (SWOT) mission, scheduled for launch in 2020, will provide... more The Surface Water and Ocean Topography (SWOT) mission, scheduled for launch in 2020, will provide a step-change improvement in the measurement of terrestrial surface-water storage and dynamics. In particular, it will provide the first, routine two-dimensional measurements of water-surface elevations. In this paper, we aimed to (i) characterise and illustrate in two dimensions the errors which may be found in SWOT swath measurements of terrestrial surface water, (ii) simulate the spatio-temporal sampling scheme of SWOT for the Amazon, and (iii) assess the impact of each of these on estimates of water-surface slope and river discharge which may be obtained from SWOT imagery. We based our analysis on a virtual mission for a ∼ 260 km reach of the central Amazon (Solimões) River, using a hydraulic model to provide water-surface elevations according to SWOT spatio-temporal sampling to which errors were added based on a two-dimensional height error spectrum derived from the SWOT design requirements. We thereby obtained water-surface elevation measurements for the Amazon main stem as may be observed by SWOT. Using these measurements, we derived estimates of river slope and discharge and compared them to those obtained directly from the hydraulic model. We found that cross-channel and along-reach averaging of SWOT measurements using reach lengths greater than 4 km for the Solimões and 7.5 km for Purus reduced the effect of systematic height errors, enabling discharge to be reproduced accurately from the water height, assuming known bathymetry and friction. Using cross-sectional averaging and 20 km reach lengths, results show Nash–Sutcliffe model efficiency values of 0.99 for the Solimões and 0.88 for the Purus, with 2.6 and 19.1 % average overall error in discharge, respectively. We extend the results to other rivers worldwide and infer that SWOT-derived discharge estimates may be more accurate for rivers with larger channel widths (permitting a greater level of cross-sectional averaging and the use of shorter reach lengths) and higher water-surface slopes (reducing the proportional impact of slope errors on discharge calculation).
Under climate change, sea-level rise and increasing storm surge intensity will increase the likel... more Under climate change, sea-level rise and increasing storm surge intensity will increase the likelihood of floods for low-lying coastal areas. Therefore, Coastal Flood Vulnerability Assessments (CFVA) are necessary to inform decision making for coastal management, where applicable. Two types of tools, hydrodynamic models and Geographic Information Systems (GIS), are commonly employed for these evaluations. Using Pigeon Point, Southwest Tobago, as a case study, this paper compares the application of both to determine the best approach for CFVA that can be used to guide coastal management. For hydrodynamic modelling, available and surveyed data on bathymetry, topography and tides along with current and future estimates of mean sea-level were used to create a structured and an unstructured grid model via the LISFLOOD-FP and TELEMAC-2D codes, respectively. For the GIS assessment, a coastal digital elevation model was developed using the same data on bathymetry and elevation. These models were used to project the present and future impact of storm surges on coastal flood extent at Pigeon Point. Outputs generated were compared and analysed within a GIS. Using predictions from TELEMAC-2D (full shallow water equations) as the baseline for comparison, average results acquired revealed that projections generated by all three models were consistent (less than 5.00% difference in flood predictions). To add certainty to the modelling results, all models were used to simulate an observed spring high tide event for model validation purposes. The Root Mean Squared Error (RMSE) was calculated as an indication of model performance. RMSE values indicated that all models were consistent and matched well to the field observations. However, further analysis revealed that inherent in the use of GIS for CFVA is hydraulic connectivity issues due to exclusion of flow dynamics, which leads to over-estimation in flood extent. Acknowledging the theory that over-estimation leads to over-management, it is suggested that hydrodynamic models are better suited for detailed CFVA, while GIS can be used rapidly as a potential indicator of flood exposure for large sites.
Jamaica, the third largest island in the Caribbean , has been affected significantly by flooding ... more Jamaica, the third largest island in the Caribbean , has been affected significantly by flooding and flood-related damage. Hence assessing the probability of flooding and susceptibility of a place to flood hazard has become a vital part of planning and development. In addition to heavy rainfall from tropical storms and Atlantic hurricanes, several terrestrial factors play significant roles in flooding, including local geology, geomorphology, hydrology and land-use. In this study, a GIS-based multi-criteria statistical methodology was developed to quantify hazard potential and to map flood characteristics. Fourteen factors potentially responsible for flooding were identified and used as initial input in a hybrid model that combined principal component analysis with logistic regression and frequency distribution analysis. Of these factors, seven explained 65 % of the variation in the data: elevation, slope angle, slope aspect, flow accumulation, a topographic wetness index, proximity to a stream network, and hydro-stratigraphic units. These were used to prepare the island's first map of flood hazard potential. Hazard potential was classified from very low to very high, nearly one-fifth (19.4 %) of the island was included within high or very high flood hazard zones. Further analysis revealed that areas prone to flooding are often low-lying and flat, or have shallow north-or northwest-facing slopes, are in close proximity to the stream network, and are situated on underlying impermeable lithology. The multi-criteria hybrid approach developed could classify 86.8 % of flood events correctly and produced a satisfactory validation result based on the receiver operating characteristic curve. The statistical method can be easily repeated and refined upon the availability of additional or higher quality data such as a high resolution digital elevation model. Additionally , the approach used in this study can be adopted to evaluate flood hazard in countries with similar characteristics , landscapes and climatic conditions, such as other Caribbean or Pacific Small Island Developing States.
Grande Riviere beach, located on the north coast of Trinidad, West Indies, is internationally rec... more Grande Riviere beach, located on the north coast of Trinidad, West Indies, is internationally recognised as a critical habitat/nesting ground for the endangered leatherback turtles (Dermochelys coriacea). Episodic extreme flooding of the Grande Riviere River led to the shifting of the river mouth and resulted in backshore beach erosion, with the most recent recorded event occurring in 2012. Following this event, the construction of a sand dam to arrest further erosion which threatened coastal infrastructure, precipitated a host of new problems ranging from beach instability to public health threats. In January 2013, high energy swell waves naturally in-filled the erosion channel, and the beach recovery continued over the successive months, thereby rendering the intervention in the previous year questionable. This paper presents a geomorphological analysis of beach dynamics for Grande Riviere, within the context of this erosion event. Data on beach profiles, sediment and coastal processes were collected using standard geomorphological techniques. Beach topographic analysis and water quality tests on impounded water in the erosion channel were conducted. Results indicate that the event created an erosion channel of 4843.42 m 3 over a contiguous area of 2794.25 m 2. While swell waves were able to naturally infill the channel, they also eroded 17,762 m 3 of sand overall across the beach. Water quality tests revealed that the impounded water was classified as a pollutant, and created challenges for remediation. Hydrologic and coastal geomorphologic interplay is responsible for the existence and sustainability of this coastal system. It is also evident that the beach system is able to recover naturally following extreme events. Our results demonstrate that effective and integrated management of such critical habitats remains dependent upon continuous monitoring data which should be used to inform policy and decision making.
This paper details research which compared rainfall data obtained from the Tropical Rainfall Meas... more This paper details research which compared rainfall data obtained from the Tropical Rainfall Measuring Mission [TRMM] to ground-based rain gauge data in northwestern Trinidad. Specifically, comparisons were made between the TRMM 3B42 (version 6) data product and rainfall data from rain gauges at the University Field Station and at the Sir Frank Stockdale building on the main campus of the University of the West Indies, St Augustine. The research was fo-cused on a TRMM grid cell which covers most of the Caroni River basin in Trini-dad. Comparisons between the data were made by using correlation tests. For each year during the analysis period 1998-2008, it was found that on a daily scale TRMM 3B42 data generally had a weak positive correlation (range of r values: 0.14-0.54) with the average rain gauge measurements. In addition, the TRMM satellite recorded fewer days per year of measured rainfall (an average of 124.1 days) as compared to rain gauges (an average of 180 days for both gauges). The average monthly rainfall measurements made by TRMM 3B42 data gave a clear representation of the differences between the dry and wet seasons in Trinidad. However, TRMM 3B42 still underestimated the rainfall measurements as compared to the rain gauge data.
The Leatherback turtle (Dermochelys coriacea) is a critically endangered species reliant on sandy... more The Leatherback turtle (Dermochelys coriacea) is a critically endangered species reliant on sandy beaches for nesting. Consequently, changes in beach morphology are a background factor in embryonic mortality. Grande Riviere beach has the highest density of nesting leatherbacks in the world, supporting a thriving ecotourist industry. The beach undergoes natural seasonal cycles of erosion and accretion, with renewal of sediment of importance to reduce diseases to eggs. Beach morphology surveys were conducted using standard surveying techniques both during and outside the nesting season, from the 2009 nesting season to the end of 2011. A survey was conducted in June 2012 to illustrate changes in the dynamics of the Grande Riviere River, and results reported here focus on a profile adjacent to the river. Relative stability was observed in the profile during the 2009 and 2011 nesting season, with 2010 displaying fluctuations in elevation throughout. In June 2012 there was a drastic decrease in estimated sediment volume of-644 m 3 due to the river changing to a westerly course.Nest loss was greatest when wave-induced erosion of beach sediment greater than 70cms in depth took place, or when river channels shifted, as in the 2012 nesting season. As stable river outlets are essential for both turtle nest preservation and the local fishing industry, the study has implications for the management of this sensitive environment.
The Surface Water and Ocean Topography (SWOT) mission, scheduled for launch in 2020, will provide... more The Surface Water and Ocean Topography (SWOT) mission, scheduled for launch in 2020, will provide a step-change improvement in the measurement of terrestrial surface-water storage and dynamics. In particular, it will provide the first, routine two-dimensional measurements of water-surface elevations. In this paper, we aimed to (i) characterise and illustrate in two dimensions the errors which may be found in SWOT swath measurements of terrestrial surface water, (ii) simulate the spatio-temporal sampling scheme of SWOT for the Amazon, and (iii) assess the impact of each of these on estimates of water-surface slope and river discharge which may be obtained from SWOT imagery. We based our analysis on a virtual mission for a ∼ 260 km reach of the central Amazon (Solimões) River, using a hydraulic model to provide water-surface elevations according to SWOT spatio-temporal sampling to which errors were added based on a two-dimensional height error spectrum derived from the SWOT design requirements. We thereby obtained water-surface elevation measurements for the Amazon main stem as may be observed by SWOT. Using these measurements, we derived estimates of river slope and discharge and compared them to those obtained directly from the hydraulic model. We found that cross-channel and along-reach averaging of SWOT measurements using reach lengths greater than 4 km for the Solimões and 7.5 km for Purus reduced the effect of systematic height errors, enabling discharge to be reproduced accurately from the water height, assuming known bathymetry and friction. Using cross-sectional averaging and 20 km reach lengths, results show Nash–Sutcliffe model efficiency values of 0.99 for the Solimões and 0.88 for the Purus, with 2.6 and 19.1 % average overall error in discharge, respectively. We extend the results to other rivers worldwide and infer that SWOT-derived discharge estimates may be more accurate for rivers with larger channel widths (permitting a greater level of cross-sectional averaging and the use of shorter reach lengths) and higher water-surface slopes (reducing the proportional impact of slope errors on discharge calculation).
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