Six Mile Creek Watershed

Drinking water in the City of Ithaca comes from the Six Mile Creek watershed, which extends southeasterly from the city about 20 miles and covers an area of approximately 52 square miles. The City of Ithaca has been working to protect the Six Mile Creek watershed for drinking water for over 100 years.

A Piece of Six Mile Creek History

This region was covered with ice during the last glacial period, concentrating water flow into valleys, including that of Six Mile Creek. The glacial retreat left a deeper Cayuga Valley, and in some areas streams cut into bedrock, forming gorges. The Six Mile Creek watershed was left with deep deposits of glacial till and clay. Throughout the 19th century, land clearing practices led to erosion that deposited more material near the stream. This sediment from natural glacial deposits and legacy erosion are picked up in rain events and give the water its brown color during high flows. Sediment removal is the largest expense for the drinking water plant. Six Mile Creek water quality is high in all other respects.

Initial attempts to find a drinking water source focused on groundwater. Streams were looked to when groundwater sources were deemed insufficient. Three reservoirs were built on Six Mile Creek between 1892 and 1911, all three relied on post-glacial gorges to support the dams. The first reservoir was a mill dam called Van Nattas, it is located at the Giles St. stream crossing. Van Nattas dam was purchased by the Ithaca Light and Water Company to bolster original water sources. More water was required as demand grew, and in 1902 the 30 foot dam was built upstream of Van Nattas in a second gorge. Finally, to acquire more storage and reduce the cost of pumping water, the 60 foot dam (Potters Fall Reservoir) was constructed in 1911. Sediment loading of the Potters Fall Reservoir led to construction of Silt Dam above Burns Rd. This dam serves as a pre-settling basin.
 

Present-Day Six Mile Creek

Today, the Potters Fall Reservoir continues to operate as designed, utilizing the gorge and gravity for water storage and delivery. The buildup of sediment in Six Mile Creek took hundreds of years of glaciation and tens of years of land clearing practices. It will take just as long for the sediment to move out of the watershed. Therefore sediment removal will be a permanent focus for the drinking water utility. Dredging of the reservoir is scheduled for 2018. The Silt Dam will also need periodic dredging. The City of Ithaca is also undertaking a Local Flood Assessment project that will look at sediment transport in Six Mile Creek and other local streams. This project may lead to upstream projects to protect water quality. City staff also partner with the Town of Caroline, USGS and Tompkins County to protect our water resources. For more information on the Six Mile Creek watershed, visit Tour Six Mile Creek. For more information on Six Mile Creek water quality or ways to get involved in protecting your local stream, visit Community Science Institute and the Community Science Data Set. For information on the Cayuga Lake watershed visit the Cayuga Lake Watershed Network.