Document Type

Article

Publication Date

1979

Abstract

Despite the Sahara being considered the most arid regions of the Earth, it witncssed a prolonged fluvial and aeolian depositional history and thus harbors subsiantial fresh groundwater resources. Such ancicnt fluvial surfaces are however. ofen concealed by acolian activities, inhibiting the discovery and mapping of potential groundwatcr rcchargel areas. On the other hand, recent advances in Synthetic A perture Radar (SAR) imagery are offering a novel approach for detecting partially hidden and dynamic landscape features. Interferometry SAR cohcrence change dctection (CCD) is a fairly recent technique that is considered as one of the most sensitive tools for mapping very slight surface changes between multi-date SAR images. Thus, this work cxplores the use of the CCD) method to investigate the fluvial ind aeolian morpho-dynamics along two sclccted [uvial paleo-channels in Egypt. Furthermore, a Ground Penctrating Radar (GPR) survey was conducted along one of the investigated fluvial channels to cal ils alternating luvial and acolian histor which provides supporting cvidence or potential gr ındy wyater accumulation suggested by the analysis ot optical Sentincl-2 and Shuttle Radar Topography Mission (SRTM) DEM data, The results show that during wetter climates, runoff causcd the crosion ol solid rocks and the rounding of sand-sired grains, which were subsequently deposited in cssions further downstream. AS the alternating dry climate prevailed, such sand deposits were reshaped into/migrating lincar sand dunes. These highly dynamic fcatures are depicted on the CCD Iwvery low coherence values close to 0 (high change), while the deposits within the associated jage ephemeral wadis show low 1e moderate coherence values ranging from 0.2 to 0,4 (high to moderate change), and the countnt rocks show relatively ne change with high coherenec values close 1o 1 The es. detected by the CCI) method. dissected their narent's stream courses and naturally 10ar (tlash tloods seasons. Pant of the dammed surface uno water may have infiltrated the ground and recharged the permeable wudi deposits. Morcover, the cquired GPR profiles across the dwadi channel show latcral and vertical changes the near-surfacc N sediments and revcal the gifterent depositional terraces, which belong distinctive fluvial periods. The alternation jof fuvial ve and acolian depositional environments- produced unique hydro-morphometrically "" trapped lakes that are very carc in arid regions but af great interest because of their significance for groundwater,recharge.

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