The author studied raised fields during two archaeological projects in 1988-91 (Rostain 1991, 1995) and in 2003-05 (Rostain and Versteeg 2003). First, aerial surveys were made with U. L.M. (photography from an ultra-light module) to identify the raised fields clusters. Then, the entire French Guiana coastal area was studied by stereoscopic analysis of about 1,500 aerial photographs. Raised fields are generally easy to detect by stereoscopy unless they are hidden by alluvium or by the forest. East of Cayenne Island there are colonial polders (wetland drained for cultivation; this technique was used extensively by the Dutch in the Suriname coastal plain), but no pre-Columbian raised fields. They are in the coastal area west of Cayenne Island, and they continue further west into Suriname. The analysis resulted in a complete map of the earthworks along the 200 km of the western coastal area (Rostain 1994) with detailed stereoscopic interpretation of several specific areas (Figure 13.6). These studies involved cooperative fieldwork with earth sciences specialists in pedology, geomorphology, hydrology, botany and topography.
Stereoscopic interpretation of aerial photographs helps to understand the human impact on the landscape. For example, photographs IGN 003.100 n° 52 and 53 of 1955 at
1:10,000 show ancient as well as recent human modifications (Figure 13.6): pre-Columbian raised fields are located between the degraded sandy ridges at about 3 m high and the swamp at about 1.3 m high, meaning the intervening surface is not too wet and not too dry. In B areas (Figure 13.6), raised fields are under the forest. It is very probable that they were constructed in the swamp. After their abandonment, alluvium (clay) was deposited and forest grew on the raised fields. On the upper slope, there are ridged fields made parallel to the slope in order to retain water, and large rounded raised fields are in the swamp. On a surface of about 5 ha to the north, raised fields are distributed in homogeneous groups of one-half ha each, which might represent areas cultivated by one family. Belt ditches are perpendicular to the retreat of flood waters. They were probably used to keep the excess water from the inundation of the swamp during the rainy season. In this manner, raised fields were protected from flooding as well as from pollution by external elements. In A areas (Figure 13.6), raised fields are partially hidden in recent alluvium from the raised fields themselves, or from the sandy ridges. A general flattening of the relief is seen in these areas.
Recent Creole remains are visible only on higher ground (Figure 13.7). A dozen gardens are located on the sandy ridges. Some of them, recently abandoned, are colonized by dense secondary vegetation. Other gardens are in full operation and enclosed to prevent cattle intrusion. The pathways on the sandy ridges are made by the cattle that come to graze. The square surrounding ditches were no longer in use when the photograph was taken. Those located near the flooded areas allowed an easy water supply. It is obvious that the modern inhabitants do not cultivate the seasonally flooded savanna and even avoid crossing these areas.
Two factors explain why some raised fields are under water today, or covered by forest: clay deposits and lack of maintenance after their use. Also, recent human activities in coastal areas have influenced and changed the landscape. For example, significant differences exist between the 1955 and 1987 aerial photographs east of Kourou River. In 1955, several rows of raised fields, belt ditches and one canal were clearly visible in the swamp at the edge of degraded sandy ridges. In 1987, they were completely invisible. U. L.M. flights over them confirm their disappearance. If these structures were visible during previous centuries, it is surprising that we cannot see them anymore now. Modern landscape changes are, of course, responsible. A dike was recently built across the savanna to connect two roads. This raised pathway significantly modified the hydrological system, allowing clay deposits to obliterate the pre-Columbian earthworks. Similar observations have been made in other areas between Cayenne Island and the Maroni River. Comparable destruction has occurred in western coastal Suriname (Werkhoven and Versteeg 1980): the construction of an east-west road in 1964 modified the natural drainage. The swamp to the south of the road was no longer subject to tidal intrusion and changed into a fresh-water zone. To the north, the road impeded the fresh-water from the south, so more sediment with salt-water came from the sea, obliterating the raised fields. Comparison of 1947 and recent aerial photographs clearly shows the destruction of many raised fields.
The second reason for the submersion of some raised fields is the absence of maintenance after their abandonment. Even if there are few erosion events in the savannas, rain can damage the structures. For example, west of Cayenne Island, raised fields are often split. This kind of destruction is enhanced by fires, which are lit each year in the savannas by modern farmers. Without the protective vegetation, a general flattening process occurs because the earth of the raised field ends up in the surrounding ditches when
Heavy rain begins. Maintenance of the raised fields requires cleaning out the ditches and depositing what is removed on top of the fields at regular time intervals. For this reason, raised fields in the wettest savannas are generally better preserved than those in the driest areas, where periodic burning followed by heavy rain is very destructive.
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