title: Modelling the long-term morphological evolution of tidal embayments

authors: van Maanen, Barend

subjects: tidal embayments

abstract: A numerical model was developed to improve the understanding of the long-term morphological evolution of tidal embayments. Morphological change was simulated as a result of the interactions between hydrodynamics, sediment transport, and the evolving topography. Numerical simulations indicate that these morphodynamic interactions can lead to the initiation of tidal channels and potentially give rise to large scale channel pattern development. The tidal range and the depth of the initially unchannelized tidal basin determined the time scale over which the channel network developed. Channels and intertidal areas rapidly formed when the basin was shallow and the tidal range large. For a large tidal range and a deep tidal basin, the tidal flow imported large volumes of sediment. The large water depths inhibited the formation of channels and the imported sediment formed a flood-tidal delta. The flood-tidal delta grew and became shallower over time until it became incised by channels. Ultimately, a complete channel network developed. Changes in the morphology of a deep basin were slowed down when the tidal range was small and the channel network then remained underdeveloped over long time scales. All the simulated morphologies, with different combinations of the tidal range and depth of the basin, evolved toward a state of less morphodynamic activity and obtained a hypsometry which resembles those of natural systems. Basins with well-developed channel networks were used to explore the response of tidal embayments to sea level rise. During sea level rise, the intertidal geometry adjusted to the changing environmental forcing conditions. Tidal channels became larger and more widely-spaced and expanded landward because of headward erosion. This landward shift of the channel network can be accompanied by a change in the asymmetry between the flood and ebb tidal currents. Sea level rise can even lead to a transition from exporting to importing sediment. These findings indicate that morphodynamic interactions need to be included in the study of sea level rise impacts on tidal systems. The morphodynamic model was extended to account for the interactions between mangroves and physical processes. Mangroves affected hydrodynamics and sediment dynamics in a variety of ways. In turn, hydrodynamic conditions controlled the colonization, growth, and dying of mangroves. Mangroves influenced channel network evolution by enhancing the branching of channels because the extra flow resistance in mangrove forests drove flow concentration and thus sediment erosion in between vegetated areas. On the other hand, mangroves hindered the landward expansion of channels. When the sea level was rising, mangroves increased the ability of areas to maintain an elevation above mid tide. Channel network expansion, induced by the rise in sea level, occurred differently when mangroves were present because they hindered both the branching and headward erosion of the expanding channels.

text: Modelling the long-term morphological evolution of tidal embayments A numerical model was developed to improve the understanding of the long-term morphological evolution of tidal embayments. Morphological change was simulated as a result of the interactions between hydrodynamics, sediment transport, and the evolving topography. Numerical simulations indicate that these morphodynamic interactions can lead to the initiation of tidal channels and potentially give rise to large scale channel pattern development. The tidal range and the depth of the initially unchannelized tidal basin determined the time scale over which the channel network developed. Channels and intertidal areas rapidly formed when the basin was shallow and the tidal range large. For a large tidal range and a deep tidal basin, the tidal flow imported large volumes of sediment. The large water depths inhibited the formation of channels and the imported sediment formed a flood-tidal delta. The flood-tidal delta grew and became shallower over time until it became incised by channels. Ultimately, a complete channel network developed. Changes in the morphology of a deep basin were slowed down when the tidal range was small and the channel network then remained underdeveloped over long time scales. All the simulated morphologies, with different combinations of the tidal range and depth of the basin, evolved toward a state of less morphodynamic activity and obtained a hypsometry which resembles those of natural systems. Basins with well-developed channel networks were used to explore the response of tidal embayments to sea level rise. During sea level rise, the intertidal geometry adjusted to the changing environmental forcing conditions. Tidal channels became larger and more widely-spaced and expanded landward because of headward erosion. This landward shift of the channel network can be accompanied by a change in the asymmetry between the flood and ebb tidal currents. Sea level rise can even lead to a transition from exporting to importing sediment. These findings indicate that morphodynamic interactions need to be included in the study of sea level rise impacts on tidal systems. The morphodynamic model was extended to account for the interactions between mangroves and physical processes. Mangroves affected hydrodynamics and sediment dynamics in a variety of ways. In turn, hydrodynamic conditions controlled the colonization, growth, and dying of mangroves. Mangroves influenced channel network evolution by enhancing the branching of channels because the extra flow resistance in mangrove forests drove flow concentration and thus sediment erosion in between vegetated areas. On the other hand, mangroves hindered the landward expansion of channels. When the sea level was rising, mangroves increased the ability of areas to maintain an elevation above mid tide. Channel network expansion, induced by the rise in sea level, occurred differently when mangroves were present because they hindered both the branching and headward erosion of the expanding channels.

year: 2011

title: Green space justice amid COVID-19: Unequal access to public green space across American neighborhoods

authors: Gao, Shuqi

subjects: COVID-19

abstract: Countries around the world have resorted to issuing stay-at-home orders to slow viral transmission since the COVID-19 pandemic. During the lockdown, access to public park plays a central role in the public health of surrounding communities. However, we know little about how such an unprecedented policy may exacerbate the preexisting unequal access to green space (i.e., green space justice). To address this research void, we used difference-in-difference models to examine socioeconomic disparities, urban-rural disparities, and mobility disparities in terms of public park access in the United States. Our national analysis using the weekly mobile phone movement data robustly suggests the following three key findings during COVID-19: (1) The elderly, non-college-educated people, poor people, and blacks are less likely to visit public parks frequently, while unemployed people appear to be the opposite. (2) Compared to rural areas, populations in urban neighborhoods appear to visit public parks more frequently and they generally go to larger parks to minimize the risk of infection. (3) Populations in neighborhoods with higher private vehicle ownership or those with a higher density of transit stops would more frequently visit and travel a longer distance to public parks during the stay-at-home order. Our results imply that conventional inequality in green space access may still exist and even become worse during COVID-19, which could negatively impact people's health during isolation. We suggest that special attention should be paid to park-poor neighborhoods during the pandemic and in the post-pandemic recovery phase.

text: Green space justice amid COVID-19: Unequal access to public green space across American neighborhoods Countries around the world have resorted to issuing stay-at-home orders to slow viral transmission since the COVID-19 pandemic. During the lockdown, access to public park plays a central role in the public health of surrounding communities. However, we know little about how such an unprecedented policy may exacerbate the preexisting unequal access to green space (i.e., green space justice). To address this research void, we used difference-in-difference models to examine socioeconomic disparities, urban-rural disparities, and mobility disparities in terms of public park access in the United States. Our national analysis using the weekly mobile phone movement data robustly suggests the following three key findings during COVID-19: (1) The elderly, non-college-educated people, poor people, and blacks are less likely to visit public parks frequently, while unemployed people appear to be the opposite. (2) Compared to rural areas, populations in urban neighborhoods appear to visit public parks more frequently and they generally go to larger parks to minimize the risk of infection. (3) Populations in neighborhoods with higher private vehicle ownership or those with a higher density of transit stops would more frequently visit and travel a longer distance to public parks during the stay-at-home order. Our results imply that conventional inequality in green space access may still exist and even become worse during COVID-19, which could negatively impact people's health during isolation. We suggest that special attention should be paid to park-poor neighborhoods during the pandemic and in the post-pandemic recovery phase.

year: 2023-02-02

title: A Māori and Pacific lens on infant and toddler provision in early childhood education

authors: Rameka, Lesley Kay

abstract: While New Zealand has made major advances in educational provision, Mäori and Pacific chil- dren continue to lag behind other groups, achieving disproportionately lower results on national averages (Marriot & Sim, 2014). Key to educational success for Mäori and Pasifika children is the acknowledgement that they are culturally located and the recognition that effective education must embrace culture. Early childhood education has an important role in building strong learn- ing foundations for young children; however, achieving this is a complex process, especially with regard to Mäori and Pacific children in early childhood education. This article outlines findings from a 2014 nationwide online survey conducted with Mäori and Pacific teachers working in Mäori and Pacific early childhood services and language nests. Respondents were asked about traditional and contemporary caregiving practices for infants and toddlers and what barriers and enablers were faced in implementing these caregiving practices within their services.

text: A Māori and Pacific lens on infant and toddler provision in early childhood education While New Zealand has made major advances in educational provision, Mäori and Pacific chil- dren continue to lag behind other groups, achieving disproportionately lower results on national averages (Marriot & Sim, 2014). Key to educational success for Mäori and Pasifika children is the acknowledgement that they are culturally located and the recognition that effective education must embrace culture. Early childhood education has an important role in building strong learn- ing foundations for young children; however, achieving this is a complex process, especially with regard to Mäori and Pacific children in early childhood education. This article outlines findings from a 2014 nationwide online survey conducted with Mäori and Pacific teachers working in Mäori and Pacific early childhood services and language nests. Respondents were asked about traditional and contemporary caregiving practices for infants and toddlers and what barriers and enablers were faced in implementing these caregiving practices within their services.

year: 2015