Conclusion and Future Research

The soil development of Thiaumont platform may not necessarily be what is expected under the Runge model and Catena concept. This is mostly due to soil texture and the relatively short time span the soil has had to develop. For the Catena concept to show heterogeneous soil development, the soil texture must allow the potential energy caused by water traveling through the profile. Soil development is accelerated by a permeable soil texture which was not seen throughout my study area. Since the top soil consisted primarily of clay, there was little water traveling through the soil profile therefore many saturated crater bottoms were seen. Clay rich soil textures impede the leaching of water into the water table. This likely explains the little variation seen in the soils water content and temperature at each recorded position within the crater.

Another major factor in soil development is time. Having been only 100 years since the initial disturbance, it is expected that at least one inch of top soil has been created. However this estimate may likely be less than what is observed as a result of the accumulation of organic litter settling within the crater bottoms.

Although the results were not as I expected, the artillery disturbance of the landscape has undoubtedly caused a different process of evolution. Future studies may in fact provide more empirical evidence supporting my hypothesis. Certain limitations within my data collection process may be overcome by different techniques of analysis.

Further research throughout the Verdun battlefield is necessary to conclude that the landscape is developing differently than in the pre-war environment. Perhaps a highly permeable study area will yield the results expected under Runge's energy model and the Catena concept.

Future researchers may find it beneficial to get ONF clearance to dig soil pits and examine the horizonation of the soil profiles. Since the soil profiles were essentially reset to day zero by the pedoturbation caused by explosive munitions, this method could clearly show how much the soils have developed since the initial disturbance. Another helpful piece of information would be knowing the location of the water table. The use of ground penetrating radar may provide valuable information in distinguishing whether or not saturated craters are at or near the water table or if soil texture is causing the retention of water.

The soils seen within the crater bottoms are also likely to be more acidic than at other locations due to the amount of tree litter. Recording the pH of each location may prove beneficial in determining how much this variable is impacting soil development.

Throughout my research I ran into a number of difficulties. This brings me to the importance of thoroughly constructing a methodology report prior to conducting field research. This process helps with any contingencies that arise so they may be overcome by a deliberate course of action. Unfortunately, not all contingencies may be preemptively recognized and the integrity of the data will perhaps depend upon a quick, formulated decision.

Runoff Results

The results of this activity provides spatial analysis of water movement and accumulation across a topographic surface. These tools effectively aid in the understanding of fluvial geography by providing spatial representations of where runoff is likely to occur and the location of the resulting drainage basins. Figure 5 shows a three dimensional representation of my study site including hydrologic characteristics that will help in my understanding of soil development under the Runge Energy Model and the Catena concept. According to this model (figure 5), soil development should be accelerated in locations labled as dark blue considering they are unsaturated (Runge). 

 

Figure 5: This three dimensional model provides a great spatial representation of the runoff characteristics of the Thiaumont Platform. The microrelief of the landscape adds to the variability in soil development in the area.

Catena Concept
There exists a relationship between soils on one part of the landscape and soils nearby. The Catena concept provides an excellent way of illustrating this geographic relationship using slope dynamics. The main components of a contena are (1) fluxes of water and matter, and (2) the location of the water table (Schaetzl, 2005). On a sloped surface, water infiltration rates depend upon the permeability of the soils and the gradient of the slope. If the slope gradient is high enough, sediments will be transported, and deposited in the form of alluvium and slopewash. The location of the water table determines how well these sediments are deposited, thus contributing to the development of the soils. 

According to the Runge Energy Model, the two most important variables for soil development are climate, and relief.  The relief of the landscape determines how the catena concept applies, and the water introduced into the system is dependant upon the climate. In artillery craters of Verdun, France both the Runge Model and the Catena Concept are used to explain soil formation in a way that promotes and/or inhibits the recovery of healthy vegetation. 

Much of the Verdun landscape is littered with craters caused by artillery fire during World War I. As a result, soil development changed in process following this initial disturbance. Soil profiles within cratered landscapes can be explained using the Runge model and the catena concept of soil development. 

Similar to the Jenny model, Runge's energy model explains soil development as a function of relief, climate, organic constituents, and time (Schaetzl, 2005). Climate and relief, being the most important factors, determine the amount of water accessible to the system and the potential energy of that water moving through the soil profile. Locations where water accumulates and permeates through the soil profile, will have better developed soils (Schaetzl, 2005). The use of Runge's energy model to explain soil development is limited by the permeability of the soil and the location of the water table. Locations with a low water table and soil textures that encourage leaching will have the most developed soil. Alongside water available for leaching is the important variable of relief. This concept is best explained using the Catena concept.

Figure 1: Pour Point analysis uses elevation data to model where water is likely to accumulate. Areas shown in light blue depict low elevations where soil moisture is highest. Using this data and the Catena concept, areas in light blue are likely to have more developed soil profiles and pronounced horizination.

Under the catena concept, soil development in areas with heavy relief depends upon the location of the water table and fluxes of water and matter within the soil profile (Schaetzl, 2005). In fully saturated crater bottoms (perched water table), soil development is slower than crater bottom well above the water table. Leached material through the soil profiles exacerbates horizonation and soil development (figure 2). As water is introduced into the soil profile, sediments are transported by colluviation and slopewash and deposited within crater bottoms (Schaetzl, 2005).  As a result, soils located within crater bottoms become more developed (Hupy, Schaetzl, 2008).



Figure 2: The catena concept explains soil development as a function of surface topography. On slope surfaces, soil development is not uniform. The movement of water through the soil profile allows for the transportation and deposition of sediments.

Microtopography, often overlooked, is a significant factor influencing soil development. Small changes in relief create pit-and-mound topography that affects variables contributing to soil development such as soil temperature, organic litter accumulation, and water infiltration/movement Schaetzl, 2005). A horizons within crater bottoms are expected to thicken as a result of the decomposition and weathering of organic materials. However, tree litter may impede the growth of vegetation as will erosive activity on crater sides. 

Data Collection Results

ArcMap was used to interpolate the surrounding elevations using complex algorithms to estimate values not physically recorded. The two methods of interpolation used were Kriging and Spline. Kriging uses a weighted algorithm dependent upon the distance between two points and their elevation values (Figure 3). Spline interpolation uses an algorithm that minimizes surface curvature and creates a model that passes exactly through each of the input values (ESRI) (Figure 4). Both interpolation methods provide a smooth and continuous representation of the area within each input point

Figure 3: A Kriging interpolation algorithm was used to estimate the elevation values between each recorded input. Kriging uses a weighted distance function to determine how output values are dependent upon the distance of multiple input values.

Figure 4: Spline interpolation estimates output values by altering the shape of a plane to pass exactly through each of the input points.

After interpolating the surrounding elevation values, the surface models were imported into ArcScene to be spatially examined in three dimensions. Both raster images were added to the program and processed to float on a custom surface as described in the previous post. This created a three dimensional model of the Thiaumont study area (Figures 5-6). 

Figure 5: Kriging interpolation of Thiaumont ridge rendered in 3D. 

Figure 6: Spline interpolation rendered in 3D. This method has a more pronounced representation of the surface because the model passes directly through each input value. 

Runoff Methodology

The process of developing a surface runoff and accumulation model consists of multiple steps. A clear and organized workflow model provides the most efficient means of communicating the process (model 1). Below the model is an explanation of each step. All tools used throughout this project may be found in the spatial analyst toolbox under hydrology and surface.



 

1) The model begins with adding a digital elevation model (DEM) to the project. My elevation model contained microtopographic relief ranging from 401 meters to 406 meters of the Thiaumont Platform, Verdun, France (figure 1). 

Figure 1: Digital Elevation Model of Thiaumont Platform. The DEM provides all of the necessary elevation data for the entire process.

 

2) The flow direction tool is used with the DEM entity to determine the direction the water will travel across the surface (figure 2). This tool is essentially calculating the aspect, the maximum angle of downslope direction (ESRI).


Figure 2: Flow direction shows the downslope angle with the steepest gradient

3a) Once the flow direction has been determined a tool may be used to locate any sinks within the watershed and fill them. Depending on the application of the research, this tool may or may not be used. For example, when observing the watershed of a large area, you may want to exclude depressions that collect surface flow. For my application, each sink (crater) was the target of my study so this step was excluded. 

3b) The flow accumulation tool is used to calculate areas with the highest rate of movement depending upon the flow direction layer (figure 3). This shows where surface runoff is most likely to occur and where it will accumulate.

Figure 3: Flow accumulation uses the flow direction to determine where water is most likely to flow across the surface.

4) After flow accumulation has been determined, the point pour tool is used to delineate the location of drainage basins (ESRI). The locations calculated in step 3b are used to determine where each microwatershed begins and ends (figure 4).


Figure 4: Pour Point uses the flow accumulation previously calculated to show drainage basins. A hillshade was applied to beter visualize the relationship between elevation and water accumulation.

Data Collection Methods

Volumetric water content, and temperatures were recorded on the cratered and non-cratered landscape. Moisture and temperature readings were collected in crater bottoms, crater sides, and crater tops (figure 1). Some areas of the landscape were so disturbed that crater tops were difficult to distinguish since they were often enveloped within one another. Coordinates of each record along with notes were organized using a Trimble Nomad global positioning system (Table 1). To minimize the amount of error involved with our equipment, volumetric water content was recorded five times for each crater position and the results were averaged together. The temperature probe was inserted 15 cm into the soil and left until the temperature stopped moving.
Figure 1: Collecting volumetric water content and temperature of the soil. Readings were taken on the crater bottoms, crater sides, and crater tops. A GPS was used to record the coordinates and characteristics of each site location.



Table 1: Each soil measurement was added to a table that is easily be imported into a GIS. The notes field consisted of various qualitative observations at that site location.


Along with soil moisture and temperature, information on the landscapes surface was also collected. Using a Total Station, we recorded accurate and precise micro elevation data to produce a three dimensional model of the surface. Elevation data was imported into an excel spreadsheet to include each points X,Y, and Z coordinates (Figure 2).
Figure 2: Using a Total Station, elevation data was recorded and compiled into an Excel file to be imported into a GIS. Each point represents the location where surface data was collected and contains an elevation (Z) field.