ONGOING ENVIRONMENTAL BASELINE STREAM ASSESSMENT PRIOR TO MANAGED SEDIMENT RELEASE FROM THE LOWER RESERVOIR, ONEONTA CREEK, ONEONTA, NY

The Lower Reservoir in Oneonta, NY, one of the main drinking water sources for the city, has been losing storage capacity due to increased sediment accumulation within the reservoir. City management is seeking to restore the storage capacity of the reservoir by flushing these accumulated sediments downstream. The environmental impacts of dam removal or reservoir flushing have scarcely been assessed. This study aims to produce a comprehensive data set for the baseline conditions of Oneonta Creek prior to sediment release in order to assess the potential effects of this practice.

Standard methods were used to analyze the sedimentology, geomorphology, water chemistry and biology of the stream at sites above and below The Lower Reservoir. Water chemistry sampling was conducted during both high and low flow conditions in 2015 and 2017.

Pebble count analysis confirmed that streambed and bar deposits contain primarily small boulders to fine gravels. There is little to no aggradation of fine sediments during dry conditions. Episodes of heavy rain or snowmelt create stream discharge strong enough to transport most fine sediments out to the Susquehanna River.

Water chemistry data from 2015 demonstrates an increase in electrical conductivity and nitrate concentrations further downstream from the reservoir during both low and high flow. This trend is likely the result of increased anthropogenic influence and drainage ditch runoff input downstream. There is little variation in pH during high and low flows at all three sites (6.15 - 6.67). 2017 data follows a similar pattern to 2015 data, with a slightly lower pH range (5.84 - 5.91).

General analysis of aquatic insect taxa data indicates greater species richness at sites upstream from the reservoir (7 identified orders, 28 different families), compared to downstream aquatic insect diversity (5 identified orders, 18 different families). This trend may be attributed to decreased stream flow and increased anthropogenic activity downstream from the reservoir.

This project examines a common problem facing reservoirs across the country. An abrupt influx of sediment into stream networks may produce unforeseen effects on downstream ecosystems and water quality. Therefore, long-term studies are important to understanding the potential impacts of this reservoir management practice.