Karst: a landform term related to blind valleys, sinkholes, closed depressions, or caves due to the dissolution of the underlying limestone or dolomite geology.
Bathgate Spring at Millbrook Marsh Nature Center
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About the Watershed
The Partner’s MS4 permit area boundary lies primarily within the Spring Creek watershed which lies in the Ridge and Valley Physiographic Province of the Appalachian Mountains. The topography is characterized by a prominent northeast-southwest alignment of a succession of steep-sided narrow ridges and valleys. Karst features are present in valleys, where they are underlain by carbonate formations. The Spring Creek Watershed is tributary to Bald Eagle Creek, which flows to the West Branch of the Susquehanna River and then ultimately to the Chesapeake Bay. Spring Creek is a head-watershed stream with a surface drainage area of approximately 146 square miles; however, the groundwater basin is considered to be approximately 175 square miles (23% larger than the surface water). Development within the watershed is approximately 14% impervious, but the town center which includes downtown State College and a large portion of Penn State is approximately 50% impervious. Future development will further stress the natural resources of the area. Because the region is not located along a major river or water source, the community is largely dependent on a sustained groundwater source. Currently 99% of the region’s drinking water comes from groundwater. The groundwater divide is temporally and spatially dynamic; and therefore, the groundwater basin may be larger or smaller at any point in time. Part of adjacent Spruce Creek surface watershed is tributary to the Spring Creek groundwater basin. While past studies have shown that surface streams can heal themselves fairly rapidly once the stresses are removed, once groundwater is contaminated it remains impaired indefinitely from a practical perspective. Fortunately, unlike many watersheds where development depletes groundwater and baseflow, the Spring Creek Watershed data show that no loss of recharge has occurred and in fact may be increasing due to the highly infiltrative nature of some of the regions soils. The Spring Creek watershed remains a world class wild trout stream fishery. Spring Creek is a heavily used sport stream fishery with fishing approximately 34 times higher than on other trout streams statewide as estimated in 2004. The continued survival of wild trout in the watershed is due to the karst geology, which is characterized by numerous limestone springs that provide year-round stream flow that moderate stream temperatures. Therefore, the MS4 Partners are equally as concerned with protecting groundwater resources as well as surface stormwater runoff. Many other karst watersheds in the State act very different than the Spring Creek Watershed, which precludes making generalizations with other karst watersheds. The vast majority of stream reaches in the Spring Creek watershed are perched above the groundwater table in the region. Large springs are located at the head of and along the course of Spring Creek. These large springs are fed primarily by diffuse groundwater flow, with some sinkhole and closed depression recharge. Some water reaches the springs through well-developed conduit-flow-dominated karst aquifer, or a combination of diffuse flow and conduit flow. Most of the small tributary valleys on the carbonate rocks of the valley floor are dry except during significant storms and snow melt periods. Sometimes during low-flow periods, many stream segments naturally go dry. |
Low head weir on Penn State Campus
One extreme example of this is the Big Hollow watershed which is a sub-basin of Spring Creek. The Big Hollow watershed, which has a total surface water drainage area of 17.1 square miles at its mouth is an under-drained carbonate valley identified as a perennial stream on USGS maps. However, the Big Hollow does not have baseflow anywhere along its length and there are no large springs. Surface runoff is primarily generated only by overland flow from impervious areas during rainfall events, with the exception of extreme runoff events or major snow melt or rain on frozen ground conditions; and therefore, it is really an ephemeral stream. The reason this phenomenon occurs in the Big Hollow is that it and its tributaries generally act as influent streams. In other words, the streambed loses water to the ground.
These same phenomena also occur in most natural minor karst drainageways in the area. However, ultimately a threshold is reached where the rate of loss within the drainageways, or infiltration, is exceeded by the peak runoff rate generated during large runoff events. Development of impervious cover can result in surface runoff occurring more frequently and traveling farther down the watershed. Pervious areas rarely, if ever, generate surface runoff; and therefore, even cornfields can have as low of runoff rates and volumes as wooded areas or meadows in other areas. Because of the lack of surface runoff, peak runoff rates and the frequency of runoff historically have been significantly overestimated in carbonate watersheds, especially for undeveloped pervious areas. This occurred because engineers applied models developed for non-carbonate areas without adjustment or calibration. This resulted in nuisance flooding immediately below most developments in the past. However, if drainageways downstream are preserved, little if any negative effects are experienced at the watershed scale. Additionally, the local Act 167 Stormwater Ordinance was specifically developed to prevent nuisance flooding.
While these facts make hydrologic changes in a carbonate watershed very different from a non-carbonate watershed, the greatest differences may be related to groundwater impacts. In carbonate areas, while the evapotranspiration (ET) component or local site recharge potential may be reduced by development activities, if the new surface runoff then reaches a sinkhole, large closed depression, or highly influent drainageway that results in recharge, the development may actually result in an increase of usable groundwater.
This can occur because the ET component that was converted to surface runoff as a result of development can become potential recharge. The induced “recharge” may unfortunately result in negative water quality impacts if the surface runoff is not able to move through renovating materials, which consist primarily of the biological active soil horizons. Additionally, if the new surface runoff enters the ground in areas where conduit flow pathways dominate, the resulting apparently recharged water may actually rapidly exit the usable groundwater, resulting in a case where development still results in reducing usable groundwater.
For these reasons, many general rules of thumb or stormwater best management practices employed elsewhere may not be the most practical in the Spring Creek Watershed. If you would like additional information or have questions, contact your municipal engineer.
These same phenomena also occur in most natural minor karst drainageways in the area. However, ultimately a threshold is reached where the rate of loss within the drainageways, or infiltration, is exceeded by the peak runoff rate generated during large runoff events. Development of impervious cover can result in surface runoff occurring more frequently and traveling farther down the watershed. Pervious areas rarely, if ever, generate surface runoff; and therefore, even cornfields can have as low of runoff rates and volumes as wooded areas or meadows in other areas. Because of the lack of surface runoff, peak runoff rates and the frequency of runoff historically have been significantly overestimated in carbonate watersheds, especially for undeveloped pervious areas. This occurred because engineers applied models developed for non-carbonate areas without adjustment or calibration. This resulted in nuisance flooding immediately below most developments in the past. However, if drainageways downstream are preserved, little if any negative effects are experienced at the watershed scale. Additionally, the local Act 167 Stormwater Ordinance was specifically developed to prevent nuisance flooding.
While these facts make hydrologic changes in a carbonate watershed very different from a non-carbonate watershed, the greatest differences may be related to groundwater impacts. In carbonate areas, while the evapotranspiration (ET) component or local site recharge potential may be reduced by development activities, if the new surface runoff then reaches a sinkhole, large closed depression, or highly influent drainageway that results in recharge, the development may actually result in an increase of usable groundwater.
This can occur because the ET component that was converted to surface runoff as a result of development can become potential recharge. The induced “recharge” may unfortunately result in negative water quality impacts if the surface runoff is not able to move through renovating materials, which consist primarily of the biological active soil horizons. Additionally, if the new surface runoff enters the ground in areas where conduit flow pathways dominate, the resulting apparently recharged water may actually rapidly exit the usable groundwater, resulting in a case where development still results in reducing usable groundwater.
For these reasons, many general rules of thumb or stormwater best management practices employed elsewhere may not be the most practical in the Spring Creek Watershed. If you would like additional information or have questions, contact your municipal engineer.
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