4 Results and Discussion

4.1 Quantitative summary

4.1.1 Raw numbers

In total, 1072 aerial photographs were examined; 1204 surface-visible palaeochannels and 34 areas of ridge and swale were recorded within the GIS database. Ten features not visible on aerial photographs were identified from parish boundary data alone.

4.1.2 Frequency of palaeochannel 'forms'

Form information (Figure 5, Table 1) was recorded for 811 surface-visible palaeochannels. Cropmark features form the most numerous group (42%), followed by dry depressions (30%), sinuous linear boundaries (19%), belts of vegetation (7%) and standing water (2%). Probable recent palaeochannels in the early stages of succession (standing water and vegetational belts) can therefore be seen to account for only 9% of the surface-visible record, with the remaining 91% occupied by undated cropmark, boundary and dry channel features. Figure 6 shows the distribution of palaeochannel forms within a sample area.

Figure 6: Surface-visible palaeochannels around the Trent-Derwent and Trent-Soar confluences, showing the distribution of recorded forms. Base map © Crown Copyright Ordnance Survey. An EDINA Digimap/JISC supplied service. [View static image]

4.1.3 Variations in palaeochannel density

Spatial variation along the valley was addressed initially at the county level, with the density of the palaeochannel resource in each county expressed as a percentage of the total survey area lying within that county (Table 2). A key difference lies between the upper/middle Trent counties (Staffordshire, Derbyshire, Leicestershire, Nottinghamshire), with densities above 2.6%, and the lower Trent counties (Lincolnshire, North Lincolnshire) with densities below 1.6%. This is clearly a factor of the deep alluvial cover in the perimarine zone. Within the middle Trent, Staffordshire and Derbyshire, with around 60% gravel terrace to 30% alluvium in the survey area, have lower densities than Nottinghamshire, where the survey area is around 60% alluvium to 30% gravel terrace. Reasons for spatial variation within the survey area can be elucidated further (Figures 7, 8, 9 and 10, Table 3) with reference to the characteristic valley forms described by Howard and Macklin (1999).