Appropriate post for New Year's Eve - resurrection of memories. What brings this about? Read on.
David Zetland sent me this photo the other day. He's currently vacationing in Egypt.
The sign conjured memories of my Fall 1995 sabbatical at Egypt's Research Institute for Groundwater, one of the twelve institutes of the National Water Research Center of the Ministry of Water Resources and Irrigation. I was at the RIGW to help them construct an environmental isotope based-groundwater model of a portion of the Nubian Aquifer. But this post is not about that project, which fell by the wayside.
While in Egypt I became aware of the problem of rising groundwater tables in Cairo and along the Nile River and at other places in Egypt. Rising groundwater levels are caused not just by the Nile's rise but also by leaking sewage and water pipes, runoff, irrigation, changes in hydroclimatology, etc.
Here is what USAID-Egypt WWW site says about antiquities preservation:
USAID has worked with its partners the Supreme Council of Antiquities and the American Research Center in Cairo to support the conservation of antiquities and archaeological sites in the Cairo area. Sites include the Mosque of Salah Tala’l, Sabil-Kuttab Muhammad ‘Ali, Bab Zuwayla, Sabil-Kuttab of Nafisa Bayda and the Aslam El-Selehdar Mosque (where conservation was undertaken by the Aga Khan Trust for Culture). USAID assistance also included the following projects at the Egyptian Museum: the upgrade of the Royal Jewelry Rooms, conservation of various statues and treasures,modernization of the museum’s conservation lab and museum management training. USAID also supported groundwater control and antiquities preservation in Old Cairo, a densely populated area that contains numerous monuments of prime importance. These monuments include Africa’s oldest mosque, Cairo’s oldest church and a synagogue. Ground water lowering helped to preserve Amr Ibn El Aas Mosque, Abu Serga Church, Mar Guirguis Church, the Roman Tower, Ben Ezra Synagogue and the Hanging Church. Ground water lowering projects around the Mosque of Salah Tala’l and Amr Ibn El Aas Mosque also addressed the problem of sewerage flooding in nearby areas which resulted in construction of sewer lines and house connections which benefitted approximately 190,000 residents living near the two sites.
Back to groundwater. One of my RIGW colleagues was working on the high groundwater table problem in areas along the Nile outside Cairo. He noted that the High Aswan Dam, although mitigating the Nile floods, also maintains the Nile's level at a generally higher level than under natural conditions. This has led to higher groundwater levels which were weakening foundations, penetrating the building materials via capillarity, the same phenomenon that causes water to rise in a straw when its bottom is immersed in a glass of water. The level in the straw rises higher than the water level in the glass; the narrower the straw, the higher the rise. The diagram shows the increasing capillary rise with time (0.5, 18, and 64 minutes) in a brick. The rise will eventually cease when the force pulling the water column up (capillarity) balances the force (gravity) pulling the column down.
Salts can also exacerbate the problem; groundwater can contain dissolved salts or dissolve them from the soil as the water table rises. The salts can promote further destruction of the building material, especially when they precipitate from the groundwater.
Here is a good article on capillarity, salt and their effects on building materials. Note how high capillarity can draw water -the theoretical limit in concrete is 10 km (that's right!).
I recall seeing an ancient building adjacent to the Nile that exhibited the above effects. The building was constructed of fine-grained (small particle sizes and pores) sandstone and the capillary effects were quite profound. The bottom few feet of the building's walls were darkened by moisture and were crumbly. The Egyptian government was working to lower the water table using pumps and drains.
Well, lesson over for today. Time to get to work on New Year's Eve dinner - my beef stroganoff!
"True teaching is not an accumulation of knowledge; it is an awaking of consciousness which goes through successive stages." - Proverb from an ancient Egyptian temple