Selected publications<\/h2>\n\t\t\t\t\n\t\t\t\t![\"RalstonGeyer_JGRES_2017\"](\"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-content\/uploads\/sites\/147\/2017\/12\/RalstonGeyer_JGRES_2017.png\" "\\"RalstonGeyer_JGRES_2017\\"")
\n\t\t\t\t<\/a>\nSediment transport in a tidal river<\/h3>\n
Ralston, DK and WR Geyer, 2017.\u00a0Sediment transport time scales and trapping efficiency in a tidal river.<\/a>\u00a0J. Geophys. Res. Earth Surface<\/em>, 122, 2042-2063. https:\/\/doi.org\/10.1002\/2017JF004337<\/a>.<\/p>\nIn many rivers, a large region of tidally influenced freshwater is located upstream from the saline estuary. We use observations and a numerical model to characterize how sediment moves through the tidal Hudson River. A sediment budget shows that about 40% of the sediment entering the tidal river remains trapped for an extended period.\u00a0High discharge events disproportionately account for the sediment that is trapped, and suspended sediment pulses during events move seaward more slowly than the river flow by a factor of 1.5 to 3. With the model we show that both the trapping efficiency and seaward transport rate depend primarily on settling velocity, which can vary by orders of magnitude from clay to fine sand. The transport rate decreases linearly with settling velocity, such that time scales for sediment to move through the estuary are several years to several decades, much greater than the variation in river discharge at event or seasonal time scales.<\/p>\n\t\t\t\t\n\t\t\t\t![\"RalstonEtal_GRL_2013_IreneHudson_satellite_365494\"](\"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-content\/uploads\/sites\/147\/2017\/11\/RalstonEtal_GRL_2013_IreneHudson_satellite_365494.png\" "\\"RalstonEtal_GRL_2013_IreneHudson_satellite_365494\\"")
\n\t\t\t\t<\/a>\nThe Hudson after Irene and Lee<\/h3>\n
Ralston, DK, JC Warner, WR Geyer, and GR Wall, 2013.\u00a0Sediment transport due to extreme events: the Hudson River estuary after Tropical Storms Irene and Lee.<\/a>\u00a0Geophys. Res. Let.<\/em>, 40(20):5451-5455, doi:10.1002\/2013GL057906.<\/p>\nRunoff from Tropical Storms Irene and Lee in 2011 introduced\u00a0about 2.7 Mton of new sediment to the Hudson River, about 5 times the\u00a0annual average. Rather than the conventional wisdom that\u00a0sediment would be trapped in the estuary, we show with observations\u00a0and a model that ~2\/3 of\u00a0the new sediment remained in the tidal freshwater\u00a0river more than a month after the storms, and only ~1\/5\u00a0reached the estuary. Instead, the high\u00a0sediment concentrations seen in the estuary were likely\u00a0due to\u00a0remobilization of bed sediment by to high stresses and reduced stratification from the storms.<\/p>\n\t\t\t\t\n\t\t\t\t![\"RalstonEtal_JGR_2012_hudsonHaverstraw_fig13_365496\"](\"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-content\/uploads\/sites\/147\/2017\/11\/RalstonEtal_JGR_2012_hudsonHaverstraw_fig13_365496.png\" "\\"RalstonEtal_JGR_2012_hudsonHaverstraw_fig13_365496\\"")
\n\t\t\t\t<\/a>\nFrontal trapping and lateral partitioning of sediment flux<\/h3>\n
Ralston, DK, WR Geyer, and JC Warner, 2012.\u00a0Bathymetric controls on sediment transport in the Hudson River estuary: lateral asymmetry and frontal trapping<\/a>. \u00a0J. Geophys Res.<\/em>, 117, C10013, doi:10.1029\/2012JC008124.<\/p>\nLateral gradients in depth, and therefore\u00a0estuarine circulation and stratification, lead to sediment\u00a0fluxes that are strongly landward in the channel\u00a0and seaward on the shoals. Bottom salinity fronts form at bathymetric expansions at multiple locations along the estuary,\u00a0and convergences at the fronts create local maxima in\u00a0suspended sediment and deposition, providing a general mechanism for\u00a0creation of secondary ETMs. Lateral sediment fluxes between channel and shoals vary with the spring-neap cycle, going\u00a0from regions of higher to lower bed stress depending on the elevation of the pycnocline\u00a0relative to the bed. Lateral and along-channel\u00a0gradients in bathymetry and thus stratification, bed stress, and sediment flux lead to an\u00a0unsteady, heterogeneous distribution of sediment transport\u00a0rather than the traditional schematic of trapping at an ETM at the salinity limit.<\/p>\n\t\t\t\t\n\t\t\t\t![\"RalstonEtal_CSR_2013_skagitStratSed_fig1_365653\"](\"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-content\/uploads\/sites\/147\/2017\/11\/RalstonEtal_CSR_2013_skagitStratSed_fig1_365653.png\" "\\"RalstonEtal_CSR_2013_skagitStratSed_fig1_365653\\"")
\n\t\t\t\t<\/a>\nSediment flux on deltaic tidal flats<\/h3>\n
Ralston, DK, WR Geyer, PA Traykovski, and NJ Nidzieko, 2013.\u00a0Effects of estuarine and fluvial processes on sediment transport over deltaic tidal flats<\/a>,\u00a0Contintental Shelf Res.<\/em>, 60, S40-S57, doi:10.1016\/j.csr.2012.02.004.<\/p>\nRiver discharge over tidal flats supplies freshwater buoyancy and\u00a0suspended sediment, and despite the extremely shallow water depths, strong salinity fronts and stratification\u00a0develop and favor flood-directed residual flows. The river discharge during low tides drains through a network of distributary channels on the exposed tidalflats with strongly ebb-directed stresses. The net sediment transport depends on the balance between estuarine and fluvial processes, and is modulated on spring-neap time scales by the tides of PugetSound. The baroclinic pressure gradient and periodic stratification enhance trapping during neap tides,while theprimary means of moving sediment off the tidal flats are the high stresses in the distributary channels during late ebb of spring low tides.<\/p>\n\t\t\t\t\n\t\t\t\t![\"RalstonGeyer_Estuaries_2009_hudsonHistoricSed_fig10_365673\"](\"https:\/\/www2.whoi.edu\/staff\/dralston\/wp-content\/uploads\/sites\/147\/2017\/11\/RalstonGeyer_Estuaries_2009_hudsonHistoricSed_fig10_365673.png\" "\\"RalstonGeyer_Estuaries_2009_hudsonHistoricSed_fig10_365673\\"")
\n\t\t\t\t<\/a>\nLong term sediment flux in the Hudson<\/h3>\n
In many rivers, a large region of tidally influenced freshwater is located upstream from the saline estuary. We use observations and a numerical model to characterize how sediment moves through the tidal Hudson River. A sediment budget shows that about 40% of the sediment entering the tidal river remains trapped for an extended period.\u00a0High discharge events disproportionately account for the sediment that is trapped, and suspended sediment pulses during events move seaward more slowly than the river flow by a factor of 1.5 to 3. With the model we show that both the trapping efficiency and seaward transport rate depend primarily on settling velocity, which can vary by orders of magnitude from clay to fine sand. The transport rate decreases linearly with settling velocity, such that time scales for sediment to move through the estuary are several years to several decades, much greater than the variation in river discharge at event or seasonal time scales.<\/p>\n\t\t\t\t\n\t\t\t\t Ralston, DK, JC Warner, WR Geyer, and GR Wall, 2013.\u00a0Sediment transport due to extreme events: the Hudson River estuary after Tropical Storms Irene and Lee.<\/a>\u00a0Geophys. Res. Let.<\/em>, 40(20):5451-5455, doi:10.1002\/2013GL057906.<\/p>\n Runoff from Tropical Storms Irene and Lee in 2011 introduced\u00a0about 2.7 Mton of new sediment to the Hudson River, about 5 times the\u00a0annual average. Rather than the conventional wisdom that\u00a0sediment would be trapped in the estuary, we show with observations\u00a0and a model that ~2\/3 of\u00a0the new sediment remained in the tidal freshwater\u00a0river more than a month after the storms, and only ~1\/5\u00a0reached the estuary. Instead, the high\u00a0sediment concentrations seen in the estuary were likely\u00a0due to\u00a0remobilization of bed sediment by to high stresses and reduced stratification from the storms.<\/p>\n\t\t\t\t\n\t\t\t\t Ralston, DK, WR Geyer, and JC Warner, 2012.\u00a0Bathymetric controls on sediment transport in the Hudson River estuary: lateral asymmetry and frontal trapping<\/a>. \u00a0J. Geophys Res.<\/em>, 117, C10013, doi:10.1029\/2012JC008124.<\/p>\n Lateral gradients in depth, and therefore\u00a0estuarine circulation and stratification, lead to sediment\u00a0fluxes that are strongly landward in the channel\u00a0and seaward on the shoals. Bottom salinity fronts form at bathymetric expansions at multiple locations along the estuary,\u00a0and convergences at the fronts create local maxima in\u00a0suspended sediment and deposition, providing a general mechanism for\u00a0creation of secondary ETMs. Lateral sediment fluxes between channel and shoals vary with the spring-neap cycle, going\u00a0from regions of higher to lower bed stress depending on the elevation of the pycnocline\u00a0relative to the bed. Lateral and along-channel\u00a0gradients in bathymetry and thus stratification, bed stress, and sediment flux lead to an\u00a0unsteady, heterogeneous distribution of sediment transport\u00a0rather than the traditional schematic of trapping at an ETM at the salinity limit.<\/p>\n\t\t\t\t\n\t\t\t\t Ralston, DK, WR Geyer, PA Traykovski, and NJ Nidzieko, 2013.\u00a0Effects of estuarine and fluvial processes on sediment transport over deltaic tidal flats<\/a>,\u00a0Contintental Shelf Res.<\/em>, 60, S40-S57, doi:10.1016\/j.csr.2012.02.004.<\/p>\n River discharge over tidal flats supplies freshwater buoyancy and\u00a0suspended sediment, and despite the extremely shallow water depths, strong salinity fronts and stratification\u00a0develop and favor flood-directed residual flows. The river discharge during low tides drains through a network of distributary channels on the exposed tidalflats with strongly ebb-directed stresses. The net sediment transport depends on the balance between estuarine and fluvial processes, and is modulated on spring-neap time scales by the tides of PugetSound. The baroclinic pressure gradient and periodic stratification enhance trapping during neap tides,while theprimary means of moving sediment off the tidal flats are the high stresses in the distributary channels during late ebb of spring low tides.<\/p>\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t<\/a>\nThe Hudson after Irene and Lee<\/h3>\n
\n\t\t\t\t<\/a>\nFrontal trapping and lateral partitioning of sediment flux<\/h3>\n
\n\t\t\t\t<\/a>\nSediment flux on deltaic tidal flats<\/h3>\n
\n\t\t\t\t<\/a>\nLong term sediment flux in the Hudson<\/h3>\n