The Esopus Creek is located in the Catskill Mountains of New York State and is part of New York City’s water supply system. In 1915 damming of a portion of the creek formed the Ashokan Reservoir splitting the creek into upper (upstream of the reservoir) and lower (downstream of the reservoir) segments. The Ashokan Reservoir watershed is 255 mi2 and is one of two reservoirs in the New York City Catskill Reservoir system and one of six reservoirs in the West-of-Hudson Catskill-Delaware system. The upper Esopus Creek watershed is approximately 192 mi2 from the source, Winnisook Lake, and the Ashokan Reservoir near Boiceville, NY, (Smith et al. 2008).
From 2009 to 2012, suspended-sediment concentrations (SSCs) and turbidity were measured at 14 monitoring sites throughout the upper Esopus Creek watershed to quantify concentrations of suspended sediment and turbidity levels, to estimate suspended-sediment loads (SSL) within the upper Esopus Creek watershed, and to investigate the relations between SSC and turbidity (McHale and Siemion 2014). In situ turbidity probes appeared to provide a good surrogate for SSC and could allow for more accurate calculations of suspended-sediment load than discrete suspended-sediment samples alone.
During the 2009-2012 study, the largest tributary, Stony Clove Creek, consistently produced higher SSCs and turbidity than any of the other Esopus Creek tributaries. The rest of the tributaries fell into two groups: those that produced moderate SSCs and turbidity, and those that produced low SSCs and turbidity. Within those two groups the tributary that produced the highest SSCs and turbidity varied from year to year depending on the hydrologic conditions within each tributary watershed.
Between 2012 and 2014, 4 reach scale stream restoration projects were completed within the Stony Clove watershed to reduce stream turbidity 1) Stony Clove at Chichester Sites 1-3, 2) Stony Clove at Stony Clove Lane, 3) Stony Clove-Warner Creek Confluence, and 4) Warner Creek Site 5. Since those projects were installed until June 2015, no flows at or exceeding bankfull discharge have been recorded in Stony Clove Creek. Therefore, it is unclear how effective the projects will be for flows at or greater than bankfull discharge. Nonetheless, there has been a measureable reduction in turbidity levels and SSCs for the range in flows experienced since the projects were installed. Re-initiating turbidity and suspended sediment monitoring along the main stem and at the major tributaries of upper Esopus Creek will allow us to evaluate the effectiveness of the stream restoration projects within the Stony Clove watershed as well as the larger upper Esopus Creek watershed. In addition, the loads from Stony Clove Creek can be put into context with the loads from all of the major tributaries to upper Esopus Creek. This proposed research will address specific requirements of the 2007-2017 Filtration Avoidance Determination (FAD) in Section 4.6 to re-initiate turbidity and suspended sediment monitoring at major tributaries and along the main channel of the upper Esopus Creek to inform stream management implementation and to help evaluate the efficacy of stream restoration practices in reducing turbidity. In November 2015, New York City Department of Environmental Protection (NYCDEP) submitted a proposal to the New York State Department of Health (NYSDOH) and the United States Environmental Protection Agency (EPA) (FAD regulatory agencies) outlining a set of studies covering a 10 year time period that will satisfy the FAD requirements (NYCDEP, 2015). The research described in this proposal is intended to provide the requisite hydrologic and water quality monitoring data and analyses for the first 5 years of the NYCDEP proposal.
The goal of this study is to characterize sources of suspended sediment and turbidity associated with changes in hydrology and differences in stream channel morphology in the upper Esopus Creek watershed. Specific objectives include:
1. Monitor SSC and turbidity levels through a range in discharge at 3 main stem locations and 5 tributaries within the upper Esopus Creek watershed and monitor turbidity levels only at an additional 2 tributaries.
2. Develop sediment and/or turbidity (dependent on the variables measured at each station) discharge rating curves for each monitoring location.
3. Estimate suspended sediment loads and yields at 8 locations within the upper Esopus Creek watershed
4. Evaluate how changes in discharge affect SSC and turbidity and examine the relation between SSC and turbidity levels, stream feature inventories.
5.. Evaluate the effectiveness of stream stability restoration projects implemented in the basin at reducing suspended sediment and turbidity.
The objectives of this project will be accomplished by collecting discrete SSC and turbidity samples throughout a range in stream discharge conditions and monitoring in situ turbidity at a 15 minute time step during a 5 year period at 8 primary monitoring stations within the upper Esopus Creek watershed. At 2 secondary stations monitoring will be confined to in situ turbidity. The monitoring stations were chosen in coordination with the NYCDEP and based on previous work in the basin (McHale and Siemion 2014). The data will be used to quantify the contribution of each tributary to the total suspended sediment load of upper Esopus Creek, to compare loads among the tributaries, and to investigate patterns in SSC and turbidity along the main channel. The 5 year monitoring period will allow the USGS to investigate how variations in discharge, season, and antecedent moisture conditions affect SSC and turbidity levels. Previously, monitoring was conducted for 3 to 5 years at many of these stations; combining previous data with the data collected during this study will allow the USGS to develop more robust sediment and turbidity rating curves. The longer data collection period will also allow us to better define the relation between suspended sediment and in situ turbidity. Because in situ turbidity is collected at a 15 minute time interval a well-defined relation between the 2 variables should allow more accurate calculations of suspended sediment loads and yields. Finally, we will also evaluate the relations among tributary SSC, SSL, turbidity and stream feature inventory data (including channel morphology, geology, and geometry).
This project will address requirements in the NYCDEP proposal to fulfill the water quality study objectives in Section 4.6 of the 2007 Filtration Avoidance Determination; specifically, to monitor suspended sediment and turbidity levels within the upper Esopus Creek watershed and its tributaries, characterize SSC and turbidity through a range in discharge at each monitoring station, and provide data to inform stream management strategies. This project will help to evaluate the effectiveness of stream restoration projects in the Stony Clove watershed and put those results into context within the larger upper Esopus Creek watershed. This project addresses several of the priorities identified in the Upper Esopus Creek Management Plan including: 1) comprehensive monitoring and surveillance of the Upper Esopus for suspended sediment, 2) information that can be used to protect, restore, enhance, or reduce impairments to aquatic habitat by helping prioritize tributaries for their contributions to suspended sediment loadings and 3) data to aid general non-point source program implementation. The project will also address the two major water quality impairments identified in the upper Esopus Creek watershed, turbidity and sedimentation within the Ashokan Reservoir watershed (CCE 2007).
This research is part of a larger evaluation of upper Esopus Creek geomorphology and stream bank stability being conducted by the New York City Department of Environmental Protection (NYCDEP) and Ulster County Soil and Water Conservation District (UCSWCD). This project fulfills the USGS Water Resources mission to provide reliable, impartial, timely information that is needed to understand the Nation’s water resources and effectively manage surface-water resources for domestic, agricultural, commercial, industrial, recreational, and ecological uses.