title: The interaction of buoyant river plumes with vegetation and consequences for sediment transport and deposition in coastal regions

authors: Vundavilli, Venkata Satya Sai Ram Hemanth

subjects: Buoyant river plumes

abstract: Mangrove forests are one of the most prominent vegetated coastal habits in tropical and subtropical areas. These wetland ecosystems typically inhabit estuaries and tidally influenced river banks. The presence of trees helps to protect coastal regions through the dissipation of tidal currents and wave energy, forming an essential barrier against coastal erosion. River plumes are the primary mechanism of sediment delivery to these vegetated coastlines. As the buoyant freshwater merges with saline ocean waters, horizontal advection of the freshwater establishes the shape of the river plume and influences the distribution of sediments along the coast. In this thesis, I investigate the principal dynamics associated with the interaction of buoyant river plumes with vegetation. In particular, we investigate the interplay between mangrove vegetation, hydrodynamics, and sediment dynamics, specifically: (1) the principal drivers of sediment deposition within a mangrove-lined river delta, (2) the influence of river forcing and winds on the sediment transport, and (3) sediment dynamics of two adjacent and interacting coastal river plumes.  

Understanding the hydro-morphodynamics of a river plume in a mangrove environment:
We developed a 3-D idealized Delft3D morphological model to explore the effects of vegetation on the river plumes and associated sediment transport patterns. Using an idealized model based on the Firth of Thames (FoT) mangrove forest located on the North Island of Aotearoa-New Zealand, we observed that, while sediment deposition occurred in the forest and tidal flats region of the model domain, the fringe region (between the vegetation and mudflat) experienced erosion. Compared to the eastern side, sediment deposition in the western side of the model domain was more prominent owing to the influence of Coriolis (Southern hemisphere). By examining the momentum balances on the surface and bottom layers in different regions of the river plume, we found that the principal balance between the bottom shear stress (enhanced by the presence of vegetation) and baroclinic pressure gradient largely controlled the sediment deposition in the riverine sections of the domain. Additionally, we found that vertical advection and diffusion during flood tide enhanced erosion in the fringe region of the mangrove forest. The advection of suspended sediment into the forest was controlled by factors including longer duration of high water slack at the forest fringe region, pressure gradients, and inertial acceleration. In the near-field region (close to the river mouth) of the river plume, during ebb tide, the barotropic and baroclinic pressure gradients coupled with Coriolis accelerations deliver sediments into the forest and mudflat regions. In the mid-field regions of the river plume, the magnitude of changes in the bed elevation was smaller due to larger Coriolis acceleration which arrested the spreading of the river plume. Furthermore, the far-field region (away from the river mouth) of the river plume experienced erosion due to more substantial tidal influence. Conversely, in the shallow forested regions, reduced movement of sediment in the offshore direction leads to an overall flood dominance.

Linking sediment transport within river plumes to varying river flows and winds:
Subsequent modeling experiments were carried out to investigate how the forcing factors of riverine discharge and wind velocities influence sediment transport within an idealized moderate-sized freshwater river plume. We assessed total sediment transport along with the relative contributions of riverine and bed-sourced sediment into a mangrove forest. Instantaneous and tidally averaged sediment fluxes were evaluated to investigate the critical linkages between the riverine flows, tidal influence, and winds in the presence of vegetation. In the near-field region of the river plume, riverine and bed-sourced sediment were dominant and found to be directed into the forest, indicative of an accretionary environment. In the mid- and far-field regions of the river plume, bed-sourced sediment was found to be the dominant contributor to total sediment transport and was directed out of the forest, indicative of sediment erosion. While the mass loads (directed into the mangrove forest) increased with an increase in riverine discharge, mass loads were relatively similar for large flow events. The river sediment delivered into the mangrove-forested regions was found to push into and through the forest front for large river discharges. The presence of 5 m/s wind velocities could alter the sediment deposition patterns in the mid- and far-field regions of the river plume. Despite the significant river momentum, strong winds (10 m/s) were also able to alter the sediment transport in the near-field region of the river plume. Moreover, results showed that in the far-field region of the river plume, strong winds combined with the effects of riverine discharge, Coriolis, and bed-shear stress affected the overall mass movement of sediment. In the case of easterly winds, a combination of tidal effects and wind stress controlled the sediment deposition into the forest. In the case of westerly winds, as the plume was pushed away from the forest, tidal effects controlled the total sediment transport. 


Understanding the effects of coalescing buoyant river plumes on sediment transport:
We investigated how the interaction between plumes from two mangrove-lined rivers in close proximity affected coastal sediment transport patterns. In particular, I examined the links between the river plume coalescence and the trapping of sediment by mangroves, using an idealized 3-dimensional numerical. Sediment fluxes and relative contributions of riverine- and bed-sourced sediments were quantified along the western, central (located between the rivers), and eastern mangrove forests. The two river plumes coalesced into a single river plume that flowed along the edge of the central mangrove forest. As the river plumes were deflected to the left by Coriolis (Southern hemisphere), the total sediment fluxes were largest for the central and the western forest, with only modest sediment deposition along the eastern mangrove forest. Also, modeled transport fluxes along the central mangrove forest were the largest close to the rivers, consistent with the satellite imagery of the FoT field site. Flow variations through either river resulted in changes to the sediment transport patterns into the mangrove forests. In particular, an increase in flow discharge through the western river resulted in reduced contributions of the eastern river towards the total sediment transport fluxes. Conversely, an increase in flow discharge through the eastern river inhibited the contribution of western river-associated sediment towards the total sediment transport flux through the central, eastern, and western mangrove forests. Furthermore, this study revealed that 5 m/s wind velocities altered the expansion, coalescence, and overall sediment transport fluxes of the river plumes. The total sediment fluxes through the central and western mangrove forests were greatest for easterly winds. However, the total transport into the eastern mangrove forest was largest for the southerly winds, as the bulge of the eastern river plume was pushed into mangrove forests.

These modeling experiments help elucidate the interaction of river plumes with mangrove vegetation. The work presented in this thesis highlights the complex non-linear interactions of hydro-morphodynamics, sediment transport, the effects of river flows and winds within mangrove environments, and the fate of riverine sediments in the bay of the Firth of Thames. Finally, the results presented here provide insights into the sediment trapping capabilities of mangroves under variable conditions and thus may help to predict their ability to function as a coastal defense mechanism under future sea-level rise and sediment supply scenarios.

text: The interaction of buoyant river plumes with vegetation and consequences for sediment transport and deposition in coastal regions Mangrove forests are one of the most prominent vegetated coastal habits in tropical and subtropical areas. These wetland ecosystems typically inhabit estuaries and tidally influenced river banks. The presence of trees helps to protect coastal regions through the dissipation of tidal currents and wave energy, forming an essential barrier against coastal erosion. River plumes are the primary mechanism of sediment delivery to these vegetated coastlines. As the buoyant freshwater merges with saline ocean waters, horizontal advection of the freshwater establishes the shape of the river plume and influences the distribution of sediments along the coast. In this thesis, I investigate the principal dynamics associated with the interaction of buoyant river plumes with vegetation. In particular, we investigate the interplay between mangrove vegetation, hydrodynamics, and sediment dynamics, specifically: (1) the principal drivers of sediment deposition within a mangrove-lined river delta, (2) the influence of river forcing and winds on the sediment transport, and (3) sediment dynamics of two adjacent and interacting coastal river plumes.  

Understanding the hydro-morphodynamics of a river plume in a mangrove environment:
We developed a 3-D idealized Delft3D morphological model to explore the effects of vegetation on the river plumes and associated sediment transport patterns. Using an idealized model based on the Firth of Thames (FoT) mangrove forest located on the North Island of Aotearoa-New Zealand, we observed that, while sediment deposition occurred in the forest and tidal flats region of the model domain, the fringe region (between the vegetation and mudflat) experienced erosion. Compared to the eastern side, sediment deposition in the western side of the model domain was more prominent owing to the influence of Coriolis (Southern hemisphere). By examining the momentum balances on the surface and bottom layers in different regions of the river plume, we found that the principal balance between the bottom shear stress (enhanced by the presence of vegetation) and baroclinic pressure gradient largely controlled the sediment deposition in the riverine sections of the domain. Additionally, we found that vertical advection and diffusion during flood tide enhanced erosion in the fringe region of the mangrove forest. The advection of suspended sediment into the forest was controlled by factors including longer duration of high water slack at the forest fringe region, pressure gradients, and inertial acceleration. In the near-field region (close to the river mouth) of the river plume, during ebb tide, the barotropic and baroclinic pressure gradients coupled with Coriolis accelerations deliver sediments into the forest and mudflat regions. In the mid-field regions of the river plume, the magnitude of changes in the bed elevation was smaller due to larger Coriolis acceleration which arrested the spreading of the river plume. Furthermore, the far-field region (away from the river mouth) of the river plume experienced erosion due to more substantial tidal influence. Conversely, in the shallow forested regions, reduced movement of sediment in the offshore direction leads to an overall flood dominance.

Linking sediment transport within river plumes to varying river flows and winds:
Subsequent modeling experiments were carried out to investigate how the forcing factors of riverine discharge and wind velocities influence sediment transport within an idealized moderate-sized freshwater river plume. We assessed total sediment transport along with the relative contributions of riverine and bed-sourced sediment into a mangrove forest. Instantaneous and tidally averaged sediment fluxes were evaluated to investigate the critical linkages between the riverine flows, tidal influence, and winds in the presence of vegetation. In the near-field region of the river plume, riverine and bed-sourced sediment were dominant and found to be directed into the forest, indicative of an accretionary environment. In the mid- and far-field regions of the river plume, bed-sourced sediment was found to be the dominant contributor to total sediment transport and was directed out of the forest, indicative of sediment erosion. While the mass loads (directed into the mangrove forest) increased with an increase in riverine discharge, mass loads were relatively similar for large flow events. The river sediment delivered into the mangrove-forested regions was found to push into and through the forest front for large river discharges. The presence of 5 m/s wind velocities could alter the sediment deposition patterns in the mid- and far-field regions of the river plume. Despite the significant river momentum, strong winds (10 m/s) were also able to alter the sediment transport in the near-field region of the river plume. Moreover, results showed that in the far-field region of the river plume, strong winds combined with the effects of riverine discharge, Coriolis, and bed-shear stress affected the overall mass movement of sediment. In the case of easterly winds, a combination of tidal effects and wind stress controlled the sediment deposition into the forest. In the case of westerly winds, as the plume was pushed away from the forest, tidal effects controlled the total sediment transport. 


Understanding the effects of coalescing buoyant river plumes on sediment transport:
We investigated how the interaction between plumes from two mangrove-lined rivers in close proximity affected coastal sediment transport patterns. In particular, I examined the links between the river plume coalescence and the trapping of sediment by mangroves, using an idealized 3-dimensional numerical. Sediment fluxes and relative contributions of riverine- and bed-sourced sediments were quantified along the western, central (located between the rivers), and eastern mangrove forests. The two river plumes coalesced into a single river plume that flowed along the edge of the central mangrove forest. As the river plumes were deflected to the left by Coriolis (Southern hemisphere), the total sediment fluxes were largest for the central and the western forest, with only modest sediment deposition along the eastern mangrove forest. Also, modeled transport fluxes along the central mangrove forest were the largest close to the rivers, consistent with the satellite imagery of the FoT field site. Flow variations through either river resulted in changes to the sediment transport patterns into the mangrove forests. In particular, an increase in flow discharge through the western river resulted in reduced contributions of the eastern river towards the total sediment transport fluxes. Conversely, an increase in flow discharge through the eastern river inhibited the contribution of western river-associated sediment towards the total sediment transport flux through the central, eastern, and western mangrove forests. Furthermore, this study revealed that 5 m/s wind velocities altered the expansion, coalescence, and overall sediment transport fluxes of the river plumes. The total sediment fluxes through the central and western mangrove forests were greatest for easterly winds. However, the total transport into the eastern mangrove forest was largest for the southerly winds, as the bulge of the eastern river plume was pushed into mangrove forests.

These modeling experiments help elucidate the interaction of river plumes with mangrove vegetation. The work presented in this thesis highlights the complex non-linear interactions of hydro-morphodynamics, sediment transport, the effects of river flows and winds within mangrove environments, and the fate of riverine sediments in the bay of the Firth of Thames. Finally, the results presented here provide insights into the sediment trapping capabilities of mangroves under variable conditions and thus may help to predict their ability to function as a coastal defense mechanism under future sea-level rise and sediment supply scenarios.

year: 2023

title: Urban outdoor water use and response to drought assessed through mobile energy balance and vegetation greenness measurements

authors: Liang, Liyin L.

subjects: Science & Technology

abstract: Urban vegetation provides many highly valued ecosystem services but also requires extensive urban water resources. Increasingly, cities are experiencing water limitations and managing outdoor urban water use is an important concern. Quantifying the water lost via evapotranspiration (ET) is critical for urban water management and conservation, especially in arid or semi-arid regions. In this study, we deployed a mobile energy balance platform to measure evaporative fraction throughout Riverside, California, a warm, semi-arid, city. We observed the relationship between evaporative fraction and satellite derived vegetation index across 29 sites, which was then used to map whole-city ET for a representative mid-summer period. Resulting ET distributions were strongly associated with both neighborhood population density and income. By comparing 2014 and 2015 summer-period water uses, our results show 7.8% reductions in evapotranspiration, which were also correlated with neighborhood demographic characteristics. Our findings suggest a mobile energy balance measurement platform coupled with satellite imagery could serve as an effective tool in assessing the outdoor water use at neighborhood to whole city scales.

text: Urban outdoor water use and response to drought assessed through mobile energy balance and vegetation greenness measurements Urban vegetation provides many highly valued ecosystem services but also requires extensive urban water resources. Increasingly, cities are experiencing water limitations and managing outdoor urban water use is an important concern. Quantifying the water lost via evapotranspiration (ET) is critical for urban water management and conservation, especially in arid or semi-arid regions. In this study, we deployed a mobile energy balance platform to measure evaporative fraction throughout Riverside, California, a warm, semi-arid, city. We observed the relationship between evaporative fraction and satellite derived vegetation index across 29 sites, which was then used to map whole-city ET for a representative mid-summer period. Resulting ET distributions were strongly associated with both neighborhood population density and income. By comparing 2014 and 2015 summer-period water uses, our results show 7.8% reductions in evapotranspiration, which were also correlated with neighborhood demographic characteristics. Our findings suggest a mobile energy balance measurement platform coupled with satellite imagery could serve as an effective tool in assessing the outdoor water use at neighborhood to whole city scales.

year: 2017-08-01

title: Te kura o Ruatoki 1896 - 1979

authors: Williams, Kim Reina Reremoana

subjects: Ruatoki Native School

abstract: Ko tēnei tuhinga roa e kōrero ana mō te Kura o Ruatoki i roto i te rohe o te iwi o Tūhoe. I whakatūria he kura i te tau 1896 i runga i te inoi a ngā Koroua ki te Kāwanatanga o taua wā.
Hai te Upoko tuatahi, ka whakatakotoria ngā kōrero mō te āhua o te whenua, ngā tāngata me ā rātau nekeneke. Tutū ana te puehu i runga i ngā whakatū waewae ki te iwi, ki te Pākehā hoki mō taua whenua.
Hai te Upoko tuarua ka takoto ngā kōrero mō te heke o ngā pānui o ngā inoi, ngā reta a ngā Koroua ki te Kāwanatanga mō te whakatū i tētahi Kura i Ruatoki. Te nuinga o ēnei rauemi i rangahaua, i kitea, i te Whare pukapuka o Pōneke. Ko ētahi i te Whare pukapuka o Tāmaki. Ka tau te tono, ka kitea te tūtukitanga o te ao Pākehā ki te ao Māori, otirā, kua puta te kaupapa i whakatūria ake ai te kura hei whakatangata whenua i ngā tāngata, i ngā aronga hinengaro Māori kia rite ki tō te Pākehā.
Hai te Upoko tuatoru ka tirohia ko ngā tuhinga a ngā Tumuaki mai i te tau 1896 ki te tau 1979 mō te Kura o Ruatoki. Ka kite i roto i ā rātau tirohanga te āhua o tā rātau kaihautū i te rerenga o te kaupapa nei. Ko ngā kaihautū i te waka nei, he tūmau noa nā te Kāwanatanga hai whakatō i te Pākehātanga ki roto i te whatumanawa Māori.
He tini o te whārua i hinga i roto i ēnei tau i runga i ngā mate urutī, mate tauhou i pā ki roto i te whārua. Ahakoa tērā ka tukuna tonu ngā tamariki ki te kura i runga i te whakapono he oranga ka puta mai i reira. I te tau 1946 ka tū he kura tuarua, he Māori District High School. Ko te nuinga o ngā tamariki o Tawera rāua ko Ruatoki i haere mai ki tēnei kura. Tokoiti ia tau i whiwhi karahipi mō te haere ki ngā kura hāhi o Tīpene rāua ko Wikitōria. Tērā pea he tango atu i ēnei tamariki mai i ngā āhuatanga Māori o te whārua.
Hai te upoko tuawhā, ka whakakorehia te kura tuarua. Ko ngā take mō te katinga ka āta whakamāramahia. He mahi nanakia nā te tari Mātauranga me āna āpiha i runga i ngā nekeneke mō tēnei kaupapa.
Hai te Upoko tuarima ka whakarerekēhia ngā marautanga ako kia tau ko te kaupapa ako i roto i ngā reo e rua ki roto i te kura. He whakautu tēnei i te kōrero a Richard Benton o te N.Z.C.E.R e kī ana, "Kāore e roa ka ngaro te reo Māori." Koinei te wā i whakapihihia ake ai te kaupapa ako i roto i ngā reo e rua, ā, ka tiritiria ko te kaupapa Rumaki Reo.
Hai te Upoko tuaono ko te kōhuretanga o te kaupapa Māori me te puāwaitanga o ngā hinengaro me ngā wairua o ngā tamariki ki te āhua o te ako i ā rātau mahi i roto i tō rātau ake reo. I tīmatahia te kaupapa i te tau 1977. Tae rawa atu ki ngā tau o muri mai kua kitea kē te huringa o ngā ngākau ki te ako.
Hai te Upoko tuawhitu ka whakaatahia mai ngā whakanekeneke i raro i tēnei kaupapa. He nui ngā tutukitanga ki ngā ture i te whakatūtanga o ngā Kura mō Āpōpō.
Hei whakarāpopototanga i ngā moemoeā me ngā tūmanako ka titiro ake ki ngā waru tekau tau kua pahemo. Kua turuki ki te pō, ki te ao. Kua noho te pukenga o te kupu kōrero, kua taipū ngā kaupapa. Ko taku mahi he whakarārangi i ngā pikinga i ngā hekenga i ngā āhuatanga katoa i mahia i roto i tēnei kura mai kore ka kitea atu he māramatanga he huarahi rānei e tiketike ake ai ngā mahi ako, ngā akoranga, ki ēnei o ā tātau mokopuna o Ngāi Tūhoe e tipu mai nei. Nō reira ka hoki rawa ngā kauhau ki ērā i whakatakotohia mai e ngā mātua tīpuna. Ka tīkina atu te kōrero i reira hai whakatinana i ngā tūmanako mō te wharekura o Ruatoki i tēnei wā.

text: Te kura o Ruatoki 1896 - 1979 Ko tēnei tuhinga roa e kōrero ana mō te Kura o Ruatoki i roto i te rohe o te iwi o Tūhoe. I whakatūria he kura i te tau 1896 i runga i te inoi a ngā Koroua ki te Kāwanatanga o taua wā.
Hai te Upoko tuatahi, ka whakatakotoria ngā kōrero mō te āhua o te whenua, ngā tāngata me ā rātau nekeneke. Tutū ana te puehu i runga i ngā whakatū waewae ki te iwi, ki te Pākehā hoki mō taua whenua.
Hai te Upoko tuarua ka takoto ngā kōrero mō te heke o ngā pānui o ngā inoi, ngā reta a ngā Koroua ki te Kāwanatanga mō te whakatū i tētahi Kura i Ruatoki. Te nuinga o ēnei rauemi i rangahaua, i kitea, i te Whare pukapuka o Pōneke. Ko ētahi i te Whare pukapuka o Tāmaki. Ka tau te tono, ka kitea te tūtukitanga o te ao Pākehā ki te ao Māori, otirā, kua puta te kaupapa i whakatūria ake ai te kura hei whakatangata whenua i ngā tāngata, i ngā aronga hinengaro Māori kia rite ki tō te Pākehā.
Hai te Upoko tuatoru ka tirohia ko ngā tuhinga a ngā Tumuaki mai i te tau 1896 ki te tau 1979 mō te Kura o Ruatoki. Ka kite i roto i ā rātau tirohanga te āhua o tā rātau kaihautū i te rerenga o te kaupapa nei. Ko ngā kaihautū i te waka nei, he tūmau noa nā te Kāwanatanga hai whakatō i te Pākehātanga ki roto i te whatumanawa Māori.
He tini o te whārua i hinga i roto i ēnei tau i runga i ngā mate urutī, mate tauhou i pā ki roto i te whārua. Ahakoa tērā ka tukuna tonu ngā tamariki ki te kura i runga i te whakapono he oranga ka puta mai i reira. I te tau 1946 ka tū he kura tuarua, he Māori District High School. Ko te nuinga o ngā tamariki o Tawera rāua ko Ruatoki i haere mai ki tēnei kura. Tokoiti ia tau i whiwhi karahipi mō te haere ki ngā kura hāhi o Tīpene rāua ko Wikitōria. Tērā pea he tango atu i ēnei tamariki mai i ngā āhuatanga Māori o te whārua.
Hai te upoko tuawhā, ka whakakorehia te kura tuarua. Ko ngā take mō te katinga ka āta whakamāramahia. He mahi nanakia nā te tari Mātauranga me āna āpiha i runga i ngā nekeneke mō tēnei kaupapa.
Hai te Upoko tuarima ka whakarerekēhia ngā marautanga ako kia tau ko te kaupapa ako i roto i ngā reo e rua ki roto i te kura. He whakautu tēnei i te kōrero a Richard Benton o te N.Z.C.E.R e kī ana, "Kāore e roa ka ngaro te reo Māori." Koinei te wā i whakapihihia ake ai te kaupapa ako i roto i ngā reo e rua, ā, ka tiritiria ko te kaupapa Rumaki Reo.
Hai te Upoko tuaono ko te kōhuretanga o te kaupapa Māori me te puāwaitanga o ngā hinengaro me ngā wairua o ngā tamariki ki te āhua o te ako i ā rātau mahi i roto i tō rātau ake reo. I tīmatahia te kaupapa i te tau 1977. Tae rawa atu ki ngā tau o muri mai kua kitea kē te huringa o ngā ngākau ki te ako.
Hai te Upoko tuawhitu ka whakaatahia mai ngā whakanekeneke i raro i tēnei kaupapa. He nui ngā tutukitanga ki ngā ture i te whakatūtanga o ngā Kura mō Āpōpō.
Hei whakarāpopototanga i ngā moemoeā me ngā tūmanako ka titiro ake ki ngā waru tekau tau kua pahemo. Kua turuki ki te pō, ki te ao. Kua noho te pukenga o te kupu kōrero, kua taipū ngā kaupapa. Ko taku mahi he whakarārangi i ngā pikinga i ngā hekenga i ngā āhuatanga katoa i mahia i roto i tēnei kura mai kore ka kitea atu he māramatanga he huarahi rānei e tiketike ake ai ngā mahi ako, ngā akoranga, ki ēnei o ā tātau mokopuna o Ngāi Tūhoe e tipu mai nei. Nō reira ka hoki rawa ngā kauhau ki ērā i whakatakotohia mai e ngā mātua tīpuna. Ka tīkina atu te kōrero i reira hai whakatinana i ngā tūmanako mō te wharekura o Ruatoki i tēnei wā.

year: 1998