Illahun Lunar Disappearance Text 10090 (A) year 3 Co-Reign of Amenemhat III
Between the forts, Semna on the west Nile bank and Kumma on the east Nile bank there are hieroglyphic marks with an inscription on the rock face. Each inscription gives the name of the king and the regnal year in association with the high water mark. These inundation marks were first discovered by Karl Richard Lepsius in 1844. Archaeologists have not found a mark for every year. Not every year was recorded it seems and some marks have fallen off or been washed away. But fifteen marks are intact covering the Middle Kingdom period. The question then arises, why was this period monitored so closely. Why were there no marks after Year 8 of Senuseret III when the fortresses were manned? Some have suggested that only the abnormally high levels of flow volumes were recorded. What constitutes normal and what is a good inundation level?
The evidence recorded at the Semna fort indicates that in the first two decades of Amenemhat’s reign, the average flood level on the Nile River rose to 17 metres, an increase of 5 metres above the normal flood level. A good flood, with water levels that were not too high and allowed for fast drainage of the flood plain would bring extra silt and expand the area of cultivation for future years. A 17 m flood was probably right on the maximum level for a good flood. A flood higher than that seems indicative of a flood that resulted in too much excess water to handle, meaning the flood plain was left inundated for a long time thus shortening the growing season for crops.