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Sedimentation in the Tijuana River Estuary (TRE) and its Relationship to Urbanization in the Watershed

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In the past four decades, the Tijuana River Watershed (TRW) has experienced significant land use change along with rapid human population growth. Rapid urbanization has resulted in sedimentation issues in Tijuana River Estuary (TRE). An earlier study in 2001 suggested that sediment accretion rates ranged from 0.7 to 1.2 cm/yr, which is high for coastal wetlands (with rates in the 1-5 mm/yr range). When sediments accumulate faster than sea level rises in estuaries, the marsh plains can become elevated enough to change tidal wetlands to upland habitats. Obtaining sediment accretion rates is important for restoration efforts protecting tidal wetland vegetation and species. In this study, by digitizing land cover from satellite imagery using ArcGIS, we estimated the size of urban areas in 1984 to be about 32,555 acres. By 2018, that value rose to approximately 94,281 acres. Since 2000, there was a 33% increase in the urban areas in the TRW. Using a DJI quadcopter and Agisoft Photoscan software, we captured imagery of the study area and processed it to create a three-dimensional terrain model with a vertical resolution of about 18 m. A small portion of the terrain model is compared with a 2014 digital elevated model (DEM) to obtain the sedimentation rates for locations without vegetation cover. We then compare these rates with land cover changes in the watershed. Our method could allow more frequent monitoring of sedimentation rates for the TRE, which is important for restoration efforts and assessment of the impacts of sea level rise.

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Sedimentation in the Tijuana River Estuary (TRE) and its Relationship to Urbanization in the Watershed

In the past four decades, the Tijuana River Watershed (TRW) has experienced significant land use change along with rapid human population growth. Rapid urbanization has resulted in sedimentation issues in Tijuana River Estuary (TRE). An earlier study in 2001 suggested that sediment accretion rates ranged from 0.7 to 1.2 cm/yr, which is high for coastal wetlands (with rates in the 1-5 mm/yr range). When sediments accumulate faster than sea level rises in estuaries, the marsh plains can become elevated enough to change tidal wetlands to upland habitats. Obtaining sediment accretion rates is important for restoration efforts protecting tidal wetland vegetation and species. In this study, by digitizing land cover from satellite imagery using ArcGIS, we estimated the size of urban areas in 1984 to be about 32,555 acres. By 2018, that value rose to approximately 94,281 acres. Since 2000, there was a 33% increase in the urban areas in the TRW. Using a DJI quadcopter and Agisoft Photoscan software, we captured imagery of the study area and processed it to create a three-dimensional terrain model with a vertical resolution of about 18 m. A small portion of the terrain model is compared with a 2014 digital elevated model (DEM) to obtain the sedimentation rates for locations without vegetation cover. We then compare these rates with land cover changes in the watershed. Our method could allow more frequent monitoring of sedimentation rates for the TRE, which is important for restoration efforts and assessment of the impacts of sea level rise.