Characterization of Stream Turbidity in the Catskills, New York: Insights into Environmental Controls

The Catskills region is an important supplier of water to the residents of New York City (NYC), as the Catskill/Delaware Watersheds contribute to more than 90% of NYC’s daily water needs. Considering that the NYC water supply system (NYCWSS) is one of the largest unfiltered surface water supplies in the world, it is imperative to ensure that high quality water is delivered to NYC for safe consumption. Stream turbidity, which is a measure of the cloudiness of water due to the light scattering from fine suspended sediments in the water column, is one parameter often examined in water quality investigations. However, maintaining high quality water in the NYCWSS is nuanced due to the multiple sources and nature of turbidity in this region. The nature of the sources of turbidity in the Catskills are largely caused by the steep topography of the region, which allows for highly erodible sediments to generate turbidity. Therefore, understanding the turbidity conditions in the Catskills is necessary to guide present-day watershed management decisions and to provide key insights into the sustainability of the NYCWSS. Previous studies have examined turbidity conditions in the Catskills, but, from our knowledge, this information has not been synthesized for the entire region. Thus, in this study, we synthesize over a decade’s worth of existing turbidity data in the Catskills to better understand the drivers of turbidity in this area. We characterized turbidity in the Catskills by examining the spatial and temporal trends in turbidity across monitoring sites, and then related these results to the existing streamflow data. Preliminary results indicate that there is a statistical difference in mean turbidity across streams; this result suggests that there may be various controls on turbidity in the Catskills, such as differences in topography, land use, and the extent of stream remediation across sites. Furthermore, after a severe flood in December 2020 in the Catskills, we found that it took approximately three months for several of the sites to return to baseline turbidity. This return to baseline turbidity was likely initiated by an intermediate streamflow event, which could clear the system of any suspended sediment from the December 2020 flood. We suggest that this is a characteristic process in the Catskills, which can provide key insights into the underlying mechanisms responsible for controlling turbidity dynamics in this region. The preliminary findings from this study provide insights into the variability of turbidity in the Catskills, which may be useful to better inform policy and engineering solutions for protecting the sustainability of the NYCWSS. Future work will involve further examination of the streamflow-turbidity relationship, as well as the implementation of a predictive model to identify the environmental controls most strongly related to the generation of turbidity in the Catskills.