Abstract
The objective of the study was to determine how gully erosion has affected the West Virginia University Core Arboretum and that Zigzag Gully experienced erosion of sediment since Gormont originally measured cross sections in 2007. The area within the Core Arboretum was made of the Coliseum, which is located in approximately 15 acres of the Arboretum property, pond, and exotic trees and shrubs. Shales are the most common rock type in the study area, with sandstones occurring in the Saltsburg Sandstone. The study realized that all the gullies are deeper on the side underlain by the shale than on the side that is underlain by sandstone, mainly due to the higher resistance of the sandstone to soil erosion. From the analysis conducted in the study, it is apparent that ZigZag gullies are similar to other gullies and that all the gullies are deeper on the side underlain by the shale than on the side that is underlain by sandstone. With the focus on shale bedrock, the study argues that erosion rates on shale bedrock are higher than erosion rates on sandstone bedrock. The gullies have rapidly eroded from the onset of coliseum in 1967. The gullies have rapidly eroded from the onset of coliseum in 1967. This conclusion has been reached after analyzing the original topographical surface and the present surface of the region. Similar to previous studies taken in regions with similar topographical challenges, human beings are advised to control the spread of gullies.
Introduction
Gully erosion attracts profound attention from the public and scientists alike due to its heightening effects in larger spatial regions than in cultivated plots. To the farmers, gully erosion results to loss of crop yields and available land, and increases workload necessary for the cultivation. Gullies are not only conspicuous in marl badlands and hilly regions; they prevail also in sandy soils and in dispersive soils (Valentin 132). According to Christensen (45), gully erosion is a form of landform especially on the hillside that is created by moving water, thereby eroding soil to resemble small valleys. Unlike ditches, gullies are usually meters in depth and in breadth (Archibold 262). During its formation process, the rate of water flow is usually substantial resulting in deep penetration action in to soil. Gully erosion is therefore the process of gully formation. When hillsides are cleared through deforestation, and other human activities, they become prone to gully erosion (Martı´nez-Casasnovas 294). Flowing water usually erodes away dislodged soil from the ground, after rainfall falls in short and intense storms in thunderstorms. Gullies may develop through head ward erosion, which results from interflow and surface runoff. Gullies are known to counter productivity of the farmland and generate sediment, which clogs downstream water bodies. Because of these effects, much effort has been invested in the study of gully erosion within geomorphology for minimization of the erosion and restoration of the landscapes.
Soil erosion is a presently an international and regional problem that has heightened with the developments of urbanization. Urbanization entails developments of urban related areas and conversion of natural physical landscape to economic land management (Sindhu 75). As an effect of urbanization, the capacity of soil to hold water reduced and the rate of runoff rate increases, which in turn results to soil erosion. Urbanization adversely affects soil erosion through diverse approaches. From the experimental studies by González (325), loose silt and earth piles, which are produced in urban construction, is easily eroded in stormy rain. In addition, effects of wind tunnel depict damage of the surface structure of dry loess causes grave soil erosion by wind in urban areas. Irrespective of the developments in an urban area, loose sandy soil and silt are washed into water bodies in ground flow during the rainy season. Anthropogenically induced soil erosion is more prevalent in the urban regions are consequences to intensive modifications during the short period.
Bedrock and slope angle has been experienced to affect erosion. Erosion is defined as the process through which soil and rock are moved because of flowing agents, water, or wind (Poesen 93). These agents move the products from the original site and lay them elsewhere through deposition process. Gravitational pull has also been known as an influence of erosion. Erosion, therefore, is a mass movement down the slopes because of gravitational force (Mangeney 3). According to Larsen, Montgomery, and Korup (247), landslides usually erode steep hill slopes on the mountain belts and the topographic relief that is generated by fluvial and glacial erosion eventually drives land sliding. Rates of estimating landslide volume can be derived from the landslide erosion and enable appraise landscape reactions to tectonic, climatic, and anthropeginic forcing (Larsen, Montgomery, and Korup 248). The scaling relationships such as power-law equations, which are applied in estimating the volume of landslide from the failure region, are generated from limited measurements. Erosion has been found to occur naturally more than, as an effect of land development, and its effects is responsible for generating the soil that sustains earth’s plants (Ormerod 1010.
Studies have shown that water level scenarios bear varying potential effects in varying shoreline types. High resistant shorelines respond to variation in soil erosion forces over longer duration than the less resistant shorelines. Bedrock shorelines are either resistant or non-resistant to the effect of varied water level scenarios. Other studies determine that silty sized particles found within most of the majority rock beds in the Arboretum are easily eroded clast size. Increased velocity and depth in the gullies in the Arboretum results to intensified erosion rates within gullies on the hillside. The purpose of this paper is to determine how gully erosion has affected the West Virginia University Core Arboretum. The study argues that Zigzag Gully experienced erosion of sediment since Gormont originally measured cross sections in 2007. With the focus on shale bedrock, the study argues that erosion rates on shale bedrock are higher than erosion rates on sandstone bedrock.
Methods
Study Area
The area within the Core Arboretum was bought by the WVU in 1948 but student research dates back in the 1920s. It was then a private entity but was opened for the public in 1954. The Core Arboretum is made of the Coliseum, which is located in approximately 15 acres of the Arboretum property, pond, and exotic trees and shrubs. Shales are the most common rock type in the study area, with sandstones occurring in the Saltsburg Sandstone.
(Gormont 80: Stratigraphic column of the Study region)
Cross-sections for the ZigZag gullies were constructed at 10 m spacing with limited linger increments where possible because of inaccessibility.
(Gormont 81: Approximate locations of Cross Sections)
Gully erosion is a form of soil erosion that began after the construction of the Coliseum in 1967 (Gormont 78). In this form of erosion, gullies appear in form of zigzag contours as illustrated in the figure below.
(Gormont 79: Illustration of the measurement of the gully erosion)
According to Donaldson (2), the Arboretum is located on a steep valley near the Monongahela River and is defined by vegetation, soil, and colluviums mask. To understand the locality, observation of the rocks is observed on the from the Boulevard section where a precise description of the rock units is presented as the Elk Lick coal, Harlem coal, Ames Shale, and limestone (Donaldson 2). The most abundant type of rock is shale with sandstone, siltstone, limestone, and coal. The shales are silty and sandy mainly with a reddish gray and kaolinite is calcareous and abundantly fossiliferous.
Data Collection
The cross sections in the study comprised of 100 m fiberglass measuring tape. Leica Rugby 100/100LR laser level with an accuracy of ± 1/16” per 100 ft) and a 7.62 m measuring rod with a Leica ROD_EYE laser detector. The measuring rod was converted to metric units for consistency in the study. Cross sections on risky areas were created through laser Technology Inc. Impulse 200 LR range-finder with an accuracy of 3-5 cm. Data for the study were collected in October 2016 from an area of 726.1 M3 with an aggradation volume of 42.8 M3. The slope of the uneroded surfaces on the erosional surfaces were measuring by inclinometer on a Silva compass. Slope measurements were extrapolated towards the center gullies to estimate original topographical regions for every cross-section. Cross-sectional regions of the eroded regions were estimated and the variation in the rough original and modern topographical. The calculated areas were applied in the calculation of the eroded volume for every 10 m of the gully down slope of each section.
Results
Figure 1: Figure showing the Cross-Sectional Area of the ZigZag Gully Erosion
Table 1: The table below shows the measurement of the Gully erosion in the Area in 2015
| Across (M) | Depth (M) | Height Above Bankfull | Depth from Bankfull |
| 0.0 | 1.82 | 0 | 1.82 |
| 0.5 | 2.09 | 0 | 2.09 |
| 1.0 | 2.43 | 0 | 2.43 |
| 1.5 | 2.86 | 0 | 2.86 |
| 2.0 | 3.16 | 0 | 3.16 |
| 2.5 | 3.7 | 0 | 3.7 |
| 3.0 | 4.13 | 0 | 4.13 |
| 3.5 | 4.99 | 0 | 4.99 |
| 4.0 | 5.02 | 0 | 5.02 |
| 4.5 | 4.89 | 0 | 4.89 |
| 5.0 | 4.72 | 4.72 | |
| 5.5 | 4.64 | 4.64 | |
| 6.0 | 4.16 | 4.16 | |
| 6.5 | 3.81 | 3.81 | |
| 7.0 | 3.94 | 3.94 | |
| 7.5 | 3.9 | 3.9 | |
| 8.0 | 3.79 | 3.79 | |
| 8.5 | 4 | 4 | |
| 9.0 | 4.31 | 4.31 | |
| 9.5 | 4.13 | 4.13 | |
| 10.0 | 3.06 | 3.06 |
Table 2: Table showing extent of Gully Erosion along the 130 cross section number in 2015
| 2015 | ||||
| Cross Section Number | Across (M) | Depth (M) | Height Above Bankfull | Depth from Bankfull |
| 130 | 0.0 | 1.81 | 0 | 1.81 |
| 130 | 0.5 | 2.19 | 0 | 2.19 |
| 130 | 1.0 | 2.71 | 0 | 2.71 |
| 130 | 1.5 | 3.13 | 0 | 3.13 |
| 130 | 2.0 | 3.37 | 0 | 3.37 |
| 130 | 2.5 | 3.66 | 0 | 3.66 |
| 130 | 3.0 | 4.35 | 0 | 4.35 |
| 130 | 3.5 | 4.57 | 0 | 4.57 |
| 130 | 4.0 | 4.99 | 0 | 4.99 |
| 130 | 4.5 | 5.22 | 0 | 5.22 |
| 130 | 5.0 | 4.92 | 4.92 | |
| 130 | 5.5 | 5.22 | 5.22 | |
| 130 | 6.0 | 5.43 | 5.43 | |
| 130 | 6.5 | 5.49 | 5.49 | |
| 130 | 7.0 | 4.58 | 4.58 | |
| 130 | 7.5 | 4.15 | 4.15 | |
| 130 | 8.0 | 3.83 | 3.83 |
Table 3: The table below compares Area of the gullies in 20007 and in 2015
| 2007 | Gormont measurement 12 | Area 2007 | Area 2015 |
| Across (m) | Depth from bankfull (m) | ||
| 0 | 0 | ||
| 0.5 | 0.12 | 0.03 | 0.9775 |
| 1 | 1.3 | 0.355 | 1.13 |
| 1.5 | 1.3 | 0.65 | 1.3225 |
| 2 | 1.32 | 0.655 | 1.505 |
| 2.5 | 1.5 | 0.705 | 1.715 |
| 3 | 1.08 | 0.645 | 1.9575 |
| 3.5 | 1.09 | 0.5425 | 2.28 |
| 4 | 1.14 | 0.5575 | 2.5025 |
| 4.5 | 1.36 | 0.625 | 2.4775 |
| 5 | 1.6 | 0.74 | 2.4025 |
| 5.5 | 1.69 | 0.8225 | 2.34 |
| 6 | 1.73 | 0.855 | 2.2 |
| 6.5 | 1.83 | 0.89 | 1.9925 |
| 7 | 0.68 | 0.6275 | 1.9375 |
| 7.5 | 0.1 | 0.195 | 1.96 |
| 8 | -0.01 | 0.0225 | 1.9225 |
| 8.5 | -0.02 | -0.0075 | 1.9475 |
| 9 | -0.21 | -0.0575 | 2.0775 |
| 9.5 | -0.6 | -0.2025 | 2.11 |
| 10 | -0.91 | -0.3775 | 1.7975 |
| -1.17 | 10.4 | -15.3 |
Figure 2: Cross Section Area of the Gully erosion at 160 m
Figure 3: Cross Sectional Area of the Gully at 230 m
Discussion
The purpose of this research was to determine how gully erosion affected the West Virginia University (WVU) Core Arboretum. The study affirms that ZigZag Gully experienced erosion of sediment since Gormont originally measured cross sections in 2007. This is evident from the findings of table 3 that compares the measurements of the gullies in 2007 and in 2005. Within the last eight years, the affected area has tripled at least with major effects seen at wider and deeper gullies. The cross-sectional area ahead of the gully is small as compared to other lower portions as depicted in table 1. The middle reaches of the gully are deep due to the large shale interval at the middle of the hillside. The lower portion of the gully is shallow due to the gentle slops at the bottom of the hillside.
With the focus on shale bedrock, the study affirms that erosion rates on shale bedrock are higher than erosion rates on sandstone bedrock. This is illustrated in figure 3 that shows the cross-sectional area at 230 m. The ZigZag gullies are similar to the rest of the gullies. The study realized that all the gullies are deeper on the side underlain by the shale than on the side that is underlain by sandstone, mainly due to the higher resistance of the sandstone to soil erosion. Figure 2 and 3 shows this variation in sandstone and in shale. This implies that shale is less resistant to erosion than sandstone. Due to absence of priori research on the region, it is challenging to determine the variation in the gullies since the development of the hillside. The gullies have rapidly eroded from the onset of coliseum in 1967. This conclusion has been reached after analyzing the original topographical surface and the present surface of the region.
Similar to previous studies taken in regions with similar topographical challenges, human beings are advised to control the spread of gullies (Archibold 263). Several approaches arise in applying this measure. Among them of the necessity to determine the effect of developing surrounding areas before any construction can be made. Human activities through urbanization in the region has added a capping layer of impermeable asphalt pavement and roofing materials that have further reduced the infiltration into the underlying soil and bedrock. The diversion of the overland flows into pipes have increased the concentration and water energy in the gullies, far more causing more erosion than natural causes. If this trend will continue in the near future, the hillside region will soon be unstable and result to landslides and falling of rocks that will endanger and abode developed area.
Conclusion
The objective of the study was to determine how gully erosion has affected the West Virginia University Core Arboretum and that Zigzag Gully experienced erosion of sediment since Gormont originally measured cross sections in 2007. From the analysis conducted in the study, it is apparent that ZigZag gullies are similar to other gullies and that all the gullies are deeper on the side underlain by the shale than on the side that is underlain by sandstone, mainly due to the higher resistance of the sandstone to soil erosion. This implies that shale is less resistant to erosion than sandstone. With the focus on shale bedrock, the study argues that erosion rates on shale bedrock are higher than erosion rates on sandstone bedrock. The gullies have rapidly eroded from the onset of coliseum in 1967.
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