Estimating Increases in Suspended Sediment Resulting from Global Climate Change: A Model from the New York City Water Supply Watershed in the Catskills

Suspended sediment is increasingly recognized as a primary pollutant of concern both for surface water-fed water supplies and aquatic ecosystems in the U.S.. The Northeast Climate Impacts Assessment (2006) forecasts increases in both frequency and magnitude of precipitation events as a result of CO2-forced climate changes. Focusing on the watersheds of the Catskills Region that contribute to the six primary reservoirs of the New York City Water Supply, a model is presented that estimates increases in watershed-scale suspended sediment loading as a result of channel enlargement consequent of these predicted precipitation changes. Stream system bankfull channel volume is approximated from a GIS-derived channel network using field-verified hydraulic geometry relations between drainage area and channel cross-sectional area. Changes in channel volume resulting from potential increases in storm flows, as predicted by GCC models, are modeled from hydraulic geometry relations between bankfull discharge and channel cross-sectional area. Increases in suspended sediment loading are then estimated from the modeled changes in channel volume and previous studies identifying the proportion of fine sediment in channel boundary material in Catskill streams.