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Tidal marsh restoration and creation has been proposed as a tool to build coastal resilience in the face of rising sea level and increasing intensity of coastal storms. However, it is unclear what conditions within constructed settings will lead to the successful establishment of tidal marsh. We used sediment cores and historical geospatial data in the tidal freshwater Hudson River to identify the rapid creation and development of marshes that are sheltered by human-made structures including railroad berms, jetties, and dredge spoil islands. These backwater areas rapidly accumulated clastic material following anthropogenic modification that allowed for transition from tidal mudflat to emergent marsh. In one case, historical aerial photos document this transition occurring in less than 18 years, offering a timeframe for marsh development. Accretion rates for anthropogenic tidal marshes and mudflats average 0.8-1.1 cm yr-1 and 0.6-0.7 cm yr-1 respectively, equivalent to 2-3 times the rate of relative sea level rise as well as the observed accretion rate at a 6000+ year old reference marsh in the study area. Paired historical and geospatial analysis revealed that more than half of all the tidal wetlands on the Hudson are anthropogenic and developed since the industrial era, including two thirds of the emergent cattail marsh. These inadvertently constructed tidal wetlands currently trap roughly 6% of the Hudson River’s sediment load. Results indicate that when sediment is readily available freshwater tidal wetlands can develop relatively rapidly in sheltered estuarine settings, and serve as useful examples to help guide future tidal marsh creation and restoration efforts.

Lacustrine sediment archives indicate that flooding during Tropical Storm Irene (2011) in the north-eastern United States caused the most severe erosion of any flood in the historic record, surpassing that of events with greater precipitation and peak discharges. Compared to deposition from historic floods, Irene's event layer was more massive and more enriched in unweathered upland sediments, indicating an anomalously high incidence of mass wasting and sediment entrainment. Precipitation records indicate that neither precipitation intensity nor total accumulation distinguished Irene from less erosive historic floods. However, cumulative precipitation prior to Irene exceeded the 95th percentile of all days in the record. When allowing for non-stationarity in the twentieth century background precipitation, we find a four-fold increase in the probability of Irene-like conditions, where impacts of extreme rainfall are enhanced by high antecedent precipitation. We conclude that irrespective of increases in extreme precipitation, the risk of highly erosive flooding in the region is increasing due to the influence of wetter baseline conditions associated with a changing climate. Copyright © 2015 John Wiley & Sons, Ltd.