The geology of the Catskill is characterized by long past sedimentation processes and the more recent influence of stream erosion on these deposits.  The bedrock of the Batavia Kill watershed were formed as predominately sedimentary rock in the middle to late Devonian Age (450 to 360 million years ago) and reflects the depositional cycles which formed the Catskill Delta. The bedrock is characterized by layers of multiple types of rock, laid in depositional cycles of  50 to 100 feet thick. The bedrock in the watershed is more predominantly exposed in the higher elevations, with unconsolidated deposits covering the bedrock in the lower elevations and on the valley floor. The bedrock of the Batavia Kill watershed is fractured, which is a benefit to those who rely on groundwater for their water needs. Typically, gray sandstones and conglomerates are found in the base of these depositional cycles followed by red sandstone, red siltstone and finally red shale or mudstone.

The soils are generally unconsolidated and dominated by various types of glacial till, as well as thick deposits of lacustrine clays and fine silt, which were deposited in glacial lakes as the ice retreated from the mountainous valleys. These unconsolidated materials have been laid upon the underlying bedrock by various processes, which are responsible for the soil characteristics present today.  The watershed soils present two primary challenges to maintaining stream stability. First, glacial tills found in the immediate stream corridor tend to be deficient in soil fines and they are often droughty making establishment of vegetation tricky. The second problem involves the deep lacustrine  clays (photos @ left) found on the valley floor. In many places in the watershed, these clays are exposed in the streambed or streambanks and when entrained in the stream system they produce significant turbidity

Soil Permeability

One of the primary influences of soils on watershed function, is related to the soils  permeability, or ability to absorb water.  In watersheds with a predominance of "tight", poorly drained soils, or soils with an impermeable fragipan layer, it is typical to see a greater runoff volume than from those soils which are more permeable.  In the Batavia Kill watershed, over 90% of the soils  are very poorly drained, and exhibit low permeability. The predominant soil types are in a hydrologic soils class of C or D, with very limited areas of better drained soils on the narrow valley floor or on alluvial terraces. C/D hydrologic drainage classes are characterized as having very low permeability, and generally the majority of the rainfall on these soils runs off to the drainage network. 

Soil Erodibility

Since stable stream systems must transport the sediment supply  from their watershed, the rate at which a watershed's soils erode and the degree to which this happens, either naturally or due to human activity, is  important to watershed managers. The soils in the Batavia Kill watershed have a moderate to severe risk for erosion.  Approximately 88% of the watershed soils are characterized as having a moderate erosion hazard or worse, with 54% classified as severe to very severe. As would be expected, the erosion hazard is directly related to soils with steeper slopes.

Essential to the understanding and management of stream systems, is an awareness that not all streams, or even stream reaches, function the same way.  Steep headwater streams such as those at the top of Big Hollow, exhibit different characteristics not only in their form but also in the manner by which they convey runoff and sediment, then lower gradient stream segments typical in the flatter sections of the watershed such as at Ashland.  Consequently, different types of streams do not respond to changes in their watershed or within the stream channel itself in the same way.  By recognizing these differences in stream form and function, watershed  managers can tailor restoration or protection strategies to the types of streams present in the watershed. 

One of the primary objectives of the Batavia Kill Stream Corridor Management Pilot Project was to test the applicability of stream classification in the Catskill watersheds. During the period from 1997 to 2000, the GCSWCD conducted hundreds of surveys on stream segments along the Batavia Kill stream.  The entire stream length was mapped using the Rosgen classification system.  In the Batavia Kill watershed, there are a range of stream types present on the main stem. In the steeper, upper most  headwaters the stream segments are predominantly "A" type streams.  These are characterized by steeper slopes low sinuosity and high entrenchment.  As the Batavia Kill flows down the valley, the slopes moderate and the valley widens and the stream types are dominated by "B" stream type.  In the middle and lower watershed, "C" stream types are dominant mixed with several fairly large sections of "B" stream.  In the lower watershed some sections of "F" stream type are also present.