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Methods and Results

A GIS base was created in order to draw up the requested environmental hazard maps for slope instability and geo-archaeology. As the pixel value increases, so too does the risk of slope instability and there is a greater chance of geo-archaeological finds.

 
SLOPE INSTABILITY
Method

Four weighted factors were combined for the slope instability mapping, selected on the basis of knowledge of the field and supplementary literature. In this region a great many factors (topography, lithology, climate, human influence, tectonics, etc.) all play a part in the development of slope instability. The most important factors that trigger mass movements are (1) slope gradient, (2) lithology, (3) proximity of faults and lineaments and (4), and proximity of thalwegs or wadis.

Slides causing large masses of material
to move down the slope


Faults due to (neo)tectonic activity

A fifth information layer consists of the locations of earlier mass movements on the slopes. This information is obtained from the geomorphological map drawn up on the basis of TK-350 images.

The various factors are then weighted by means of a statistical calculation based on the site of earlier mass movements. The highest weight is given to the factor with statistically the greatest influence on mass movements in the region.


Geomorphological map resulting from
mapping based on stereoscopic TK-350-images

The geomorphological mapping based on TK-350 images serves a double purpose:
(1) A general mapping (1:100,000) of the whole canyon; and
(2) A detail mapping (1:50.000) of the dam site and immediate canyon environment. The legend is based on the geomorphological legend for semi-arid and arid regions developed at the University of Saragossa (Spain).

The geomorphological map on a scale of 1:50,000 was checked in the field during a second survey. At the same time, field research was carried out into faults and other lineaments which provide evidence of neotectonic activity in the region.

Results

Danger of landslides!
The sum of these weighted layers results in a map which shows the spatial variation for the relative risk of mass movements or landslides. For greater clarity, the map is classified into 4 risk categories (low risk, moderate risk, high risk and very high risk) on the basis of the image histogram.


Slope instability risk map indicating the site
of the planned dam (height of the dam: 10 to 50 m)


Block diagram of the digital terrain model including the planned reservoir

The planned dam construction in the Wadi Mujib will create an upstream reservoir whose volume will be dependent on the dam height. The very unstable slopes already present a potential danger of further landslides, the result being that the reservoir will progressively lose its capacity due to sediment infill. In addition, by raising the water table, the marly canyon walls will become moist (with a higher pore pressure) making the present slope instability even worse. As there is increased contact between the future lake and the high risk zones, there is a considerably increased danger of slope instability for dam walls of above 20 meters in height.

 
GEO-ARCHEOLOGICAL CARTOGRAPHY

Method

What is a good archeologist's spot?
A model similar to that for slope instability is drawn up for the geo-archaeological mapping. In this case, however, there is no statistical calculation and thus no weights are allocated. The model consists of 8 information layers on the spatial variation of possible locations of as yet undiscovered archaeological sites or artefacts :

- The proximity of the steep plateau rim: the location of most known sites indicates the strategic importance of the plateau rim. From here there is a good view of the surrounding area and protection from attacks from the opposite side by the deep canyon.

- The proximity of the important King's Highway: this trading route dating back several thousand years has already yielded many archaeological finds.

- The proximity of thalwegs or wadis: these are important for the supply of water.

- The gradient: the flatter the terrain, the more likely it is to be attractive to people to settle there.

- The lithology: the presence of basalt (on which fertile earth develops) or fertile alluvium is very likely to attract people.

- The proximity of a water source, a seepage line, or of Pleistocene travertine indicates the previous presence of water: this is important for the water supply.

- The river terrace remnants: the low gradient and presence of a fertile valley bottom results in the formation of terraces which are an ideal place for agriculture or settlement.

- The slope direction : in hot climates people seek out shaded areas. Since the Neolithic revolution the protecting vegetation has been removed, leaving overgrazed and bare slopes. North-facing slopes are exposed to less sunlight, certainly resulting in a lower evaporation level (= higher moisture content of the soil) than on south-facing slopes. East and west-facing slopes have a value between the two.

The TK-350 images are a valuable aid in pinpointing these landscape elements.

  


The archaeological site of Lehun is located on the northern edge of Wadi Mujib, overlooking the canyon which is 700 m deep and 5 km wide


Travertine sediments (in situ) along the valley sides


Fluviatile terraces and current river bed
Results

This is where to dig!
By combining these information layers it is possible to produce a map which shows the spatial variation of the likelihood of archaeological sites or artefacts being present. The relevance of the resulting geo-archaeological map is tested by comparing the location of already known archaeological excavations with the probability map. For the test zone it appears that 52% of the known sites lie in the zone of very high probability; the remaining 48% in zones with average to high probability. No known site is located in zones with a low to very low probability!

It can be assumed that building the dam will result in the loss of a great deal of archaeological material on the river terrace remnants and the alluvial deposits. Archaeologists can use the geo-archaeological map of the dam site as a guide in organising an effective emergency excavation campaign.


Map of probable archaeological sites indicating the
site of the planned dam (height of the dam: 10 to 50 m)
Conclusion

The combination of the geomophological interpretation of the TK-350 images and field work in drawing up a geomorphological map (and derived landslide map) provides the necessary qualitative basic information with which to draw up a general slope instability model. The TK-350 images also provide an important added value when creating a geo-archaeological model for the location of terrace remnants, alluvium, travertine deposits, the steep plateau rim, etc. Even if time and/or money prevents a field survey, the TK-350 images provide sufficient qualitative information for the geomorphology on a scale of £ 1:50,000.

It can be concluded that the use of stereoscopic TK-350 images brings two major benefits, namely:

1. They can be effectively used for geomorphological preliminary studies for environmental risk mapping.

2. For various reasons, they are more useful than stereoscopic aerial photographs (£ 1:50,000): the lower price (especially for large areas), shorter delivery period (just 1 month!) and image processing, and less complexity (advantage of large coverage and metric indications on the images).