how a river changes its characteristics when it reaches the lowland
Upland and lowland Upland habitats are cold, clear, rocky, fast-flowing rivers in mountainous areas; lowland habitats are warm, slow-flowing rivers found in relatively flat lowland areas, with water that is frequently coloured by sediment and organic matter.
Flooding of the Nile Whilst the earliest Egyptians simply laboured those areas which were inundated by the floods, some 7000 years ago, they started to develop the basin irrigation method. Agricultural land was divided into large fields surrounded by dams and dykes and equipped with intake and exit canals. The basins were flooded and then closed for about 45 days to saturate the soil with moisture and allow the silt to deposit. Then the water was discharged to lower fields or back into the Nile. Immediately thereafter, sowing started, and harvesting followed some three or four months later. In the dry season thereafter, farming was not possible. Thus, all crops had to fit into this tight scheme of irrigation and timing.