Other adverse ecological consequences 1. Increased lateral erosion in the river
Erosive activities in the Nile course increased owing to the river’s greater
velocity of flow, which was enhanced by the reduced amounts of sediments
transported. Formerly the deposited silt had continuously smoothed out the
surface of the river bed, thus reducing the water turbulence and the river’s
erosivity. Great damage occurred particularly to the dams and locks down-
stream, so that some of them had to be replaced by stronger ones.
2. Deepening of the river bed and sedimentation within the Nile course
The changed run-off in the Nile and in the irrigation canals not only caused
stronger lateral erosion but also led to a deepening of the river bed in some
places and to the formation of islands in others. The latter enhanced the
growth of aquatic plants, such as the fast-growing water hyacinth and vari-
ous reeds. This is particularly adverse to Nile navigation, especially during
low water levels in winter. To make navigation in that season possible, about
2.5 billion m3
 of water which cannot be used for irrigation purposes in winter
have to be discharged additionally from the High Dam Lake. Moreover, the
water plants, which also spread in the irrigation canals, cause greater water
loss through increased evapotranspiration. Thousands of fellaheen are today
occupied all year in eradicating the water hyacinth, once introduced in Africa
for the sake of amenity but harmful in the course of time. Needless to say,
during the eradication of the plants the fellaheen wade in the water, thus ex-
posing themselves to the risk of infection with bilharzia (see below).