SURFICIAL GEOLOGY OF A CRITICAL REACH IN WARNER CREEK, PHONECIA, NY, AND ITS POTENTIAL IMPACT ON NEW YORK CITY'S DRINKING WATER SUPPLY

The surfical geology of Warner Creek was investigated during the summer of 2010 by students participating in the SUNY New Paltz REU program. Warner Creek is a tributary of the Esopus Creek which supplies fresh water to New York City from the Catskill Mountains in upstate New York. Warner Creek appears to be a significant contributor of fine suspended sediments to the reservoir. To better understand the origin of the suspended sediments a lower reach of Warner Creek which contained an apparent point source of fine sediments was mapped and modeled in three dimensions using field observations, well logs, GIS, and GPR.

Detailed terrace mapping reveals at least three sets of fluvial terraces marked by distinct risers and some preserved former channels. An uppermost terrace appears erosional with no preserved terrace sand & gravel; the underlying sediment is a red till. Other terraces truncate either lacustrine silt-clay or red till. A widespread valley red till unit can be distinguished from hill slope gray till. The valley till unit truncates an underlying lacustrine silt-clay and incorporates lacustrine sediment in the till matrix. Well logs gathered from government agencies and drilling companies were compiled to build a three-dimensional model of the subsurface sediments. Several trends could be identified, including a thick unbroken layer of clay blanketing the valley floor and the possible presence of multiple tills. At the surface GPR data collected with 100 & 200 MHz antennae show 2-3 m of alluvial sand and gravel with prograding bars filling buried channels cut into clay. The GPR signal is quickly attenuated by the clay. It was found that the lacustrine sediments were extensive and the primary source of the suspended sediments in Warner Creek.