الفهرس 
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Abstract
The High Aswan Dam has been in operation since 1964. When the flood reaches lake Nasser the velocity of water DROPs from more than 1 m/sec. to about 0.02 m/sec. This considerable fall
leads to the deposition of about 98 % of the suspended matter in the lake formed by Aswan dam. The bed egredation from 1964 up to 1971 reached 0.22, 0.41, 0.24, and 0.27 m downstream
Aswan dam, Esna ba r ra-jc , Nag-Hammadi barrage, and Assuit
barrage respectively. For the same sites the maximum DROP in the water level of the Nile was 0.40, 0.80, 0.58, and 0.50 m respectively. The degredation downstream Esna barrage has been recovering since 1973 at the rate of 3 to 4 cm/year. This result of such lowering in water surface elevation is an increase of the effective head on the barrages, which endanger its stability [53]. The recommended solution of this problem is to construct subsidiary weirs downstream the existing barrages to reduce the total head affecting the barrages and
net uplift pressures under them [53]. It is suggested to construct a subsidiary weir provided with a sloping middle apron because of the existence of scour holc~ downstream
existing barrages. The two consecutive structures are founded on two pervious strata. The lower stratum is of very high permeability than the upper one, which is found in most Egyptian regions [16].