So far numerous studies to predict river bed degradation downstream of Old Aswan Dam "OAD" were extensively carried out. However, variation of both of river bed and water surface levels downstream of "OAD" with time and location since the construction of high Aswan Dam "HAD" till now has not been fulfilled. For this reason, the present study was carried out to identify the occurred variations in bed and water surface levels through the first reach which is located from downstream of "OAD" to upstream of Isna barrages. In order to fulfill the study objective, the daily records of flow discharges and the corresponding water surface levels along the first reach from year 1962 to 2010 were utilized to deduce the matching stage discharge rating curves.
Comparison of the deduced water surface levels for various periods and locations along the reach - at passing 200 million m3 / day – revealed that El-Gaafra and Kom - Ompo gauge stations were the only subjected sites to degradation since "HAD" construction which turned over and recovered to sedimentation at years 2002 and 1991 for El-Gaafra and Kom – Ompo respectively and reached to a maximum value of 0.0111 and 0.315 m at El- Gaafra and Kom – Ompo in year 2010. On the other hand, the downstream part of the study reach did not subject to any degradation since "HAD" construction till year 2010. The monitored sedimentation (deposition) within such reach in year 2010 reached a maximum value of 0.760, 0.989 and 1.405 m at Selwa – Bahary, El – Ramady, and Edfu gauge stations respectively with respect to the condition before "HAD" construction. Moreover, water surface slope – through the studied reach at passing flow discharge of 200 millions m3/day – was reduced from 5.84 cm/km in year 1962 to 4.05 cm/km in year 2000 . The achieved results concluded that the first Nile River reach is being subjected to sedimentation and not degradation after "HAD" construction.
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