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The
Spring Creek Watershed is Defined by Both Ground-Water and Surface-Water Boundaries
The area of the Spring Creek Watershed is 146 square miles when the surface-water boundary is used to define the watershed. The surface-water boundary is the location where a drop of rain falling onto the ground surface splits, and one-half flows overland and through tributary stream channels to Spring Creek, and one-half of the raindrop flows overland (in the opposite direction) to a stream in an adjacent watershed such as Bald Eagle Creek watershed. The area of the Spring Creek Watershed as defined by its ground-water boundary is 175 square miles, which is 20 percent larger than the surface-water watershed area of 146 square miles. A ground-water boundary is similar in concept to a surface-water boundary, except it is the location on the water-table surface where a drop of water (which has infiltrated into the subsurface) splits when it reaches the water-table surface, and one-half of the drop flows (as ground water) to a stream bed or spring which flows into Spring Creek, and one-half of the drop of ground-water recharge flows in the opposite direction to a stream bed or spring in an adjacent watershed such as Spruce Creek. Watershed boundaries are also called drainage divides, because they are the location where surface-water or ground-water flow divides and flows in opposite directions. The ground-water and the surface-water boundaries of the Spring Creek Watershed are shown on the map below:
On the mountain ridges the surface-water and ground-water drainage divides are coincident, because ground water flows in the same direction as the surface water. On the floor of Nittany Valley and Penn’s Valley, where the underlying bedrock is limestone, ground-water flow is controlled by caverns in the bedrock. The southwestern ground-water divide boundary of Spring Creek Watershed is located several miles beyond the surface-water divide, because subsurface caverns and solution openings in the limestone bedrock drain the ground water in this area to the northeast. Ground-water recharge that occurs throughout several square miles of the adjacent Spruce Creek Surface-Water Watershed flows underground to the northeast through the caverns and conduits developed along a fault zone and discharges at Big Spring. Thus the headwaters of Big Spring are located beneath the area of State Game Lands 176 in Halfmoon and Ferguson Townships. The limestone and dolomite areas of the valley floor are shown on the geologic map of the Spring Creek Watershed below:
In Penn’s Valley, subsurface caverns in the limestone bedrock drain some of the ground-water recharge within the Spring Creek Watershed surface-water drainage basin into Sinking Creek, in the adjacent Penn’s Creek Watershed. Therefore the area of Spring Creek Watershed is reduced in the vicinity of Old Fort and Tusseyville due to the subsurface drainage of ground-water to Sinking Creek. Throughout the entire Spring Creek Watershed, ground water seeps into the beds of streams and flows from the many springs. This is how ground-water becomes surface water flowing in the stream channels. The tributary streams feed into Spring Creek, which flows out of the watershed at the McCoy Dam near Milesburg. Approximately 86 percent of the total annual flow of Spring Creek is ground water before it becomes surface water. This very high percentage of former ground water in our streams illustrates the important role of ground water in the Spring Creek Watershed and in the flow of Spring Creek.
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