GRADUAL RECOVERY FROM FLOOD DISTURBANCE RECORDED IN SEDIMENT CORES

New York City supplies ~4E6 m³ of water per day to 9 million users making it the largest surface water supply in the U.S. to operate under a Filtration Avoidance Permit. Persistent elevated turbidity in the Esopus Creek watershed, which feeds the Ashokan Reservoir (~22 % of system storage), presents challenges to maintaining an unfiltered water supply. Significant resources are currently being put towards understanding and mitigating turbidity sources in the upper watershed.

Here we present results from sediment cores from the Ashokan Reservoir that show up to nine distinct event deposits since 1950, each representing erosion from a historical flood. There is only a limited relationship between event peak discharge and corresponding layer thickness, suggesting that catchment erosion is controlled by various factors besides flood intensity. Event layer thickness increases to the present, despite variable magnitude in flood discharge. Clastic inputs from the most recent event and flood of record (Tropical Storm Irene, 2011) continue to the core top (2017) and suggest that these event layers do not represent a one-time sediment pulse, but rather the sum of flood derived sediment and that from the watershed’s gradual recovery.