مروحة وادي الباب بالجزء الجنوبي الغربي من الجبل الأخضر شمال شرق ليبيا : دراسة جيومورفولوجية باستخدام تقنيات الجيوانفورماتكس

Abstract EN

This study deals with the geomorphology of the alluvial fan of Wadi Albab.

Field study, examination and classification of satellite images and analysis of digital elevation model (DEM) of fan surface have shown that the surface elevation vary between 71.09 - 112.59 meters above the sea level and it inclines at 0.26 - 2.58 degrees.

The inclination of the surface of the fan to the southwestern direction and southern occupy about 17.6% 16.7% of the study area respectively, other directions to the northeast and east account for 15.6% and 14.6% of the area.

Morphometric analysis of fan’s surface indicates that the fan area is about 186.4 km2 , so it is classified as giant fan.

The length of its circumference is 52 km, it’s width along the middle part is 18.6km, and at its main outlet is 2.4km., and the length of its axial axis is 13.7 km.

The analysis has also shown that the fan have the following parameters; elongation factor is 1.12, circulation factor is 0.86, form factor is 0.99 and compactness coefficient is 1.07.

The drainage basin area of wadi Albab is 1056 km2 .

The common features on fan surface are; mid channel bars, braided stream channels, sand dunes, knoll-dunes, gravels blankets and vegetation.

Dimensions and geographic distribution of these features as well as area that they cover are considerably vary.

Classification of satellites images for the extent of these features have shown that the gravel blankets occupy most parts of the fan surface area about 32.8% and the plants cover only about 1.55%.

Grain size analysis of fan sediments indicating that it vary between 65 to 850 microns.

The grain size 65 micron (equivalent to 4 Ø) comprising most of the samples, it constituting about 32.8% and 41.7% in surface sample (2) and subsurface sample (2) respectively.

The analysis also showed that fine sand size material forming about 88.8%.

Grain size parameters derived using Folk & word 1952 equations indicating the following, the sediments are poor to very poorly sorted، as they comprise about 77.8% of the samples, the well sorted to very well-sorted sediments constituent only 22.2% of the samples.

Most of samples (about 88.9%) showing negative skewness indicting that they are consisting of mainly fine material.

Most of samples have strong kurtoses due to composition of fine material.

This study deduced three geomorphic development stages through which the alluvial fan of wadi Albab has passed, the first stage, through which initial building of the fan and the appearance of primary features (post Gunz – Pleistocene), the second stage include the development of the middle and distal zones of the fan (10,000 – 4000 B.C.- Holocene).

The third stage; during this period wind geomorphic features have appeared (3000 B.C.

to present time).

The utilitarian value of fan appears in many forms; the agricultural use; cultivation of wheat, barley, olive, vine and fig crops.

The utilization its deposits as quarries for pavement material.

Attraction site for tourist activities, include geomorphic features, the old Castle on top of the cliff that overlook the fan, the flat areas that can be exploited as local airport and playgrounds for various sports.