Analysis of the land and water resources of the Campus begins with an understanding of the regional physiography and the geology from which it is derived. Physiography describes the form of the land surface — the response of the original bedrock to uplift by the forces of plate tectonics and by erosion by eons of rainfall that has sculpted the different rock types into hills, valleys, plateaus and ridges. The flow and movement of water underground is also controlled by the geology, as the system of fractures in the bedrock creates flow pathways which carry water underground as ground water and back to the surface as springs and seeps.
The University of North Carolina at Chapel Hill is located in both Orange and Durham Counties, in a transitional area located between two physiographic regions — the piedmont and the coastal plain. The landforms of this area, known as the North Central Piedmont, are described as a “vast plain of rolling knolls and hillocks dissected gently by minor streams, more boldly by the creeks and rivers” (Godrey p.12). The Campus includes all of these landforms from the broad, flat plateaus where the University was first located, to the wide, low-lying floodplains of Morgan Creek, in the southeastern portion of the Mason Farm Property.
Two major geologic formations underlie the University of North Carolina at Chapel Hill Campus.
- Dense metamorphic granitic formations in the western part of the region,
- Triassic formations in the east.
Figure 13 shows an overlay of drainage sub-basins for the Campus over the bedrock, and illustrates the relationship between bedrock and watersheds. Local watersheds are not divided along the boundaries of different rock types, but only reflect local landforms and surface drainage pathways. However, regional drainage is from the west to east, reflecting the slope of the land down towards the ocean, flowing to the Triassic basin and then southeast to the coastal plain.
Soils that have weathered from these two major geologic formations reflect both the parent rock and the climatological conditions that form them. These soils are fully described in the Orange County Solis Report, and are only briefly summarized here.
In most of the Historic Core, urban soils predominate on made-land and its properties are extremely site-specific. These soils are the product of the grading and mixing that often accompanies development. It is typical to find almost 18 inches of fill in these areas. These soils arc often heavy clays with a tendency to shrink and swell, and are frequently compacted by human use. This land and the soil porosity have been significantly altered from its natural form through cutting and filling practices. The drainage patterns and inflltration rates must be determined by site investigations and soil testing on urban soils.
In the southern portion of Main Campus, the Appling Soil Series predominates. These soils are moderately well drained and have a low organic matter content in the surface layer and are not as susceptible to erosion. These soils support the forests of the steeper valley slope that are of particular hydrologic value. These remaining forested areas are a critical recharge source for both Meeting of the Waters and Morgan Creek.
On the floodplain of the Mason Farm property, the soils were formed from the fine materials washed from the uplands. In these areas the water table is very near the surface and these soils are frequently waterlogged. Chewacla and White Store soils predominate in this area which has a high water table of 0.5 to 1.5 feet from the surface of the land. Over forty percent of the Mason Farm property lies within the 100 year floodplain and is within the Town of Chapel Hill Resource Conservation District (RCD).
The streams we see today on the University property are only remnants of the natural drainage patterns that existed historically. However, even buried streams continue to influence drainage patterns because groundwater follows long established sub-surface pathways, regardless of where the piped stream has been re-directed.
According to historic University maps provided by the Facilities Planning Department, an extensive stream network flowed through the undeveloped region now known as South Campus. College Branch, a tributary of Meeting of the Waters Creek, originated slightly west of the Venable Building. and flows southeast under South Road, before linking up with its main stem. This tributary flows directly underneath the Kenan Memorial Stadium, built in the late 1920s. When constructed, a series of under-drains were built to keep the stadium field dry. As the necessary expansion and growth of the University occurred, other natural stream channels have been buried and put in pipes. As pressure to accommodate the automobile grew along with the development in the southern end of the Main Campus. many of the small stream valleys were filled in and paved over for parking.
Two large important stream valleys are presently preserved at the University as open space – Battle Creek in Battle Creek Park at the northeastern end of the Campus and the Meeting of the Waters Creek in the Pinetum on the western border. A remnant valley of a tributary of College Branch also remains today, located just west of the Bell Tower and east of the Bell Tower Parking Lot. Unfortunately, in its current state, the storm drain system outlets to this small relic stream.
As illustrated previously, the University is located within the larger Cape Fear River Basin. Specifically, the southern-most portion of the Campus is located within sub-basin 6, as identified by the North Carolina Division of Water Quality (DWQ). This sub-basin includes Morgan Creek. Meeting of the Waters Creek, and Bolin Creek, along with large sections of the town of Chapel Hill. Sub-basin 6 drains entirely to Jordan Lake, which drains to the Haw River, which flows into the Cape Fear River. In comparison with other sub-basins in the Cape Fear River basin, sub-basin 6 contains a large proportion of urban areas.
Biological assessment data from Morgan Creek indicate a downstream decline in water quality. Good or excellent water quality results are recorded from upstream sites, and Fair or Poor bio-classification ratings appear as the stream flows through the urban and suburban sections of Chapel Hill. Meeting of the Waters is identified as not supporting (NS), because of an impaired biological community. In stream habitat, degradation, along with urban non-point source pollution, is the probable cause of this impairment. In addition, two segments of Morgan Creek are identified as partially supporting (PS) and not supporting (NS) because of an impaired biological community. Possible causes of impairment are identified as sedimentation and urban non-point source pollution.
Cycles of flood and drought are a natural process, but the current practices of land development greatly increase these impacts on the hydrologic cycle. The Environmental Master Plan identifies areas of the University where this cycle has been altered by existing land practices and estimates the potential of future impacts. It also suggests methods and approaches to planning and design that will restore that balance, and with it the health of the entire water system.
Historic maps of the Campus reveal that an extensive stream network once flowed through the region of Main Campus south of South Road. College Branch, a tributary of Meeting of the Waters Creek, originated slightly west of the Venable Building and flows southeast under South Road, before linking up with its main stem. This tributary currently flows directly underneath the Kenan Memorial Stadium; when the stadium was constructed in the late 1920s, a series of under-drains were built to keep the stadium field dry and interconnected with the now buried stream.
As development pressures and the need to accommodate the automobile grew, other small stream valleys were filled in and paved over for parking. These buried streams continue to influence drainage patterns because groundwater follows long-established sub-surface pathways, regardless of where the piped stream has been redirected.
The southern portion of the Campus is comprised of sub-basins that contain a high percentage of impermeable surfaces. This has exacerbated the amount and speed of stormwater runoff, as well as the amounts of non-point source pollutants that reach Morgan Creek. The consequences downstream, including the North Carolina Botanical Garden, the Mason Farm Biological Reserve, and adjacent community parks such as Jones Park, are severe. In particular, stream channels have migrated and their banks are destabilized as they adjust to handle the increased water volume, increased velocities and the increased sediment load.
The vegetation of the floodplain corridor is also severely impacted by the change in the hydrologic balance. Many species, such as beech and oak, are dependent upon closeness to the water table in order to weather times of drought and cannot survive continued lowered table conditions. If adequate levels of recharge are not sustained over time, changes in vegetation are likely. These conditions are a direct result of the engineering of runoff and illustrate the consequences of failing to include the conservation of natural hydrologic patterns.