4.4. Comparing the inclination results from transect study and from the map study

Correspondingly to Menberu, et al., (2016), GW depth of 30 cm was considered the threshold for whether a location is currently wet enough to be considered as part of a wetland, and peat present in the soil, an indication that the location has been wet enough to support wetland vegetation in the past. These two parameters were found to correlate to a high degree across all three cases and this strong correlation is thus an indication that all three cases have been successfully restored to a pre-ditching state.

No measurements of inclination were made for this study. Instead, the elevation model of Denmark (The Danish Agency for Data Supply and Efficiency (b), 2022) was used. Aligning this model with measurements in the field proved to be impossible to do accurately with the chosen tools. The accuracy of the GPS logger was too unprecise, so manual adjustment of the geo-references of the transects was needed. The use of compass and 20 m measuring tape in the field study was an assertion that the transects were positioned in cardinal directions and that sample spots were at the designated distances from each other, but their accurate position on a map could not be assured. It was expected to find a clear relation, where a lower inclination would result in a more wet soil. No such relation was found, but because of the uncertainty of the inclination data, vvvvvvv the results of the transect inclination are inconclusive.

The map study of inclination of the whole case areas was made as an alternative method to the unprecise method of plotting inclination of the transects onto the elevation model, as well as to study the inclination of the case areas as a whole. By making polygons in QGIS of the SCALGO rain fill and using the elevation model to make polygons at a 10 cm higher altitude in QGIS, the difference and relative difference in size between the two polygon areas was found for the three cases. A larger relative difference does roughly correspond with a lower general inclination. The relative difference was largest at Case 3, suggesting that area having the lowest general inclination.

However, since the altitude difference is fixed on 10 cm, the scaling of the area affects the inclination. This means that a large area has a lower inclination than a small area if the relative difference in size is the same. Case 2 has the largest area out of the three cases, and when calculating the general inclination here, it was found to have been lower than it was at Case 3. The calculation performed to get to this result made use of the assumption of areas with circular shape. However, none of the three cases have a shape that is remotely circular, so the calculations do not correspond well with the actual situation. The calculated inclination of the map study was found to be approximately 1/10 of the mean transect inclinations (table 9).

Table 9: Comparison of inclination results from the two different methods. “Difference between methods (%)”shows how much greater the inclination of the transect study is compared to the map study.