Proper characterization of river flow is essential for the development of structural and non-structural measures to reduce flood damages, restore ecosystem functions, and manage environmental contaminants in riparian zones. The duration of flood events is an important feature that drives riverine processes and functions such as erosion, geomorphic adjustment, habitat suitability, and nutrient and water quality dynamics. Despite this, most flood characterization methods focus on relating the magnitude of annual-maximum discharges to frequency, without addressing the duration of flood events. We investigated event-specific discharge-duration dynamics at 33 USGS stream gages within the US state of Vermont. Building on the method of Feng et al., 2017, , flood events from 15-min discharge timeseries were extracted using an automated threshold method. A statistical model was fit at each gage for both frequency of discharge exceedance and conditional duration of discharge exceedance. This Duration-Over-Threshold model estimates the arrival rate of a discharge threshold, q, being exceeded for a given duration, d. Fitted model parameters were compared to basin and channel physiographical characteristics to develop regional regression equations and examine potential watershed processes underlying the duration dynamics. Model parameters summarizing event duration were best predicted by drainage area, mainstem slope, and soil depth/type. The regional regression equations enable design event estimation in ungaged catchments of the study region, which may be used to improve the predictive capacity of hydraulic and ecosystem models, outline a range of potential geomorphic trajectories, or inform emergency management plans and flood damage rating curves.

The 2021 Cyclone Seroja was a category 3 storm that made landfall on Lembata Island, causing extensive damage. This study aims to identify key interpretations of sediment transport related to tropical cyclones (TC) Seroja and past floods using a geopedological approach, estimate the return period through frequency analysis, and determine the rainfall threshold for flooding using HEC-RAS software. Extreme rainfall data from global precipitation model (GPM) (2000-2023) in Wei Laing watershed were analysed alongside LiDAR terrain data, physical and chemical properties of soil, and land cover data. Based on geopedological analysis, the result shows that the erosional-transfer zone of Wei Laing Watershed has thin, loamy, and slightly sandy soils due to erosion and limited pedogenesis. The depositional zone contains flood deposits with abrupt vertical texture changes, reflecting transported coarse grains and finer in-situ sediments. The modern flood deposit (TC Seroja flood deposit) was identified by texture, CaCO3 content, organic matter, and coarse organic material. The fine-grained flood deposits (<_ 4 cm) are classified as slackwater deposits, consist of silty clay loam and silt loam textures, reflecting deposition under slow-flowing conditions. TC Seroja corresponds to a 50-year return period. Hydrological modelling indicates a 60 mm/day rainfall threshold for flooding, with 77 flood events recorded between 2000-2023. The model is confirmed by thick past flood deposits enriched with coarse organic materials. These findings provide insight into flood dynamics and sedimentary responses, supporting future flood risk mitigation efforts.

High-latitude permafrost regions store large stocks of soil organic carbon (OC), which are vulnerable to climate warming. Estimates of subsurface carbon stocks do not take into account floodplains as unique landscape units that mediate and influence the delivery of materials into river networks. We estimate floodplain soil OC stocks within the active layer (seasonally thawed layer) and to a maximum depth of 1 m from a large field data set in the Yukon Flats region of interior Alaska. We compare our estimated stocks to a previously published data set and find that the OC stock estimate using our field data could be as much as 68% higher than the published data set. Radiocarbon measurements indicate that sediment and associated OC can be stored for thousands of years before erosion and transport. Our results indicate the importance of floodplains as areas of underestimated carbon storage, particularly because climate change may modify geomorphic processes in permafrost regions.

Floodplains accumulate and store organic carbon (OC) and release OC to rivers, but studies of floodplain soil OC come from small rivers or small spatial extents on larger rivers in temperate latitudes. Warming climate is causing substantial change in geomorphic process and OC fluxes in high latitude rivers. We investigate geomorphic controls on floodplain soil OC concentrations in active-layer mineral sediment in the Yukon Flats, interior Alaska. We characterize OC along the Yukon River and four tributaries in relation to geomorphic controls at the river basin, segment, and reach scales. Average OC concentration within floodplain soil is 2.8% (median = 2.2%). Statistical analyses indicate that OC varies among river basins, among planform types along a river depending on the geomorphic unit, and among geomorphic units. OC decreases with sample depth, suggesting that most OC accumulates via autochthonous inputs from floodplain vegetation. Floodplain and river characteristics, such as grain size, soil moisture, planform, migration rate, and riverine DOC concentrations, likely influence differences among rivers. Grain size, soil moisture, and age of surface likely influence differences among geomorphic units. Mean OC concentrations vary more among geomorphic units (wetlands = 5.1% versus bars = 2.0%) than among study rivers (Dall River = 3.8% versus Teedrinjik River = 2.3%), suggesting that reach-scale geomorphic processes more strongly control the spatial distribution of OC than basin-scale processes. Investigating differences at the basin and reach scale is necessary to accurately assess the amount and distribution of floodplain soil OC, as well as the geomorphic controls on OC.