BASELINE STUDIES OF SEDIMENTOLOGIC, GEOMORPHIC, AND HYDROLOGIC PARAMETERS OF ONEONTA CREEK, ONEONTA, NY PRIOR TO SEDIMENT RELEASE

Capacity in the Lower Reservoir in Oneonta, NY has decreased significantly by sediment infill. The city government is considering drawdown flushing as a means to remove sediment as opposed to dredging owing to expense limitations. The release of a large amount of sediment could have a negative impact on the downstream ecosystem of Oneonta Creek, so making a pre-release assessment of various stream parameters is necessary to characterize the properties of the stream, as well as predict the potential for fine sediment aggradation.

Analyses of water chemistry, sedimentology of bar deposits, and geomorphology were conducted at sites above and below the reservoir. Water conductivity (63.3-72.5 mS/cm upstream and 127.6-220.5 mS/cm downstream) and TSS (0-7.8 mg/L upstream and 1.1-12.9 mg/L downstream) values increase moving downstream during both high and low flow regimes, possibly due to drainage ditch runoff and other anthropogenic influences, which are more prevalent downstream. During low flow, nitrate concentration above the dam is 0.26 mg/L, then drops to 0 mg/L directly below the dam, and finally increases to 0.64 mg/L farther downstream, showing removal of nitrates in the reservoir and then reacquisition of them downstream. The stream bed and bar deposits mainly consist of small boulders to gravel. These large particles couldn’t be sieved, but the median size of the sieved particles was still small to medium sized gravel. The percentage of silt and smaller sized particles is very low for all samples, the greatest having a little more than two percent by weight.

Below the reservoir, discharge is near zero during dry conditions and very high from heavy rains and snowmelt in the spring. When discharge is low, it is so low that there is little aggradation of any sediment. When discharge is high, it is so high that any fines that may have accumulated during lower flows are carried out to the Susquehanna River.

It is likely the City of Oneonta is not the only municipality with the issue of sedimentation within a reservoir in the region. If other local municipalities also decide to release sediment from their reservoirs, large amounts of stored sediment can end up in the Susquehanna River, and eventually the Chesapeake Bay, potentially having harmful effects on the Chesapeake Bay ecosystem.