Lecture in the 11th International Conference of Meroitic Studies

The Hafir as a Water Clarification Device

Vienna, 1-4 september, 2008

 

Among the identifying seals of the Meroitic civilization the rain water reservoirs, the hafīrs, stands notoriously. Their presence near ancient urban centers in the Butana was indicated from the first reports, although they have not been object of detailed descriptions. In the 70´s and 80´s of the last century, the articles of Kleinschroth enlivened the attention on the matter, and in the 90´s Hinkel offered two interesting synthesis. Only in the last years the mission of the Humboldt Universität in Musawwarat underwent a systematical and coherent study of the local great hafīr.

Certainly we ignore almost everything about these devices. A fact is beyond doubt, nonetheless: their dimensions prove a technical ability and a high degree of organization that only could be held by a powerful state structure, with economic resources and manpower apt to build and to maintain them. In this way it has been sustained that the hafīrs could represent structures certainly functional but also symbolic of the Meroitic state power, like the amphitheatres could have been for the Roman Empire.

The lack of precise information on the rest of the meroitic reservoirs lays many questions without answer. To begin with, if we could assume as their purpose to store water runoff after occasional rains, it could be debatable the use given to the water stored, and opinions run from the employment for cattle and human drinking, to their connection with cotton crops, as was suggested by Abdalla (1984).

Since they are in an intermediate location between hills from which could arrive the water runoff, and urban areas, the hafīrs could also have been stood as a defense against possible alluviums, to limit their destructive power.

If we cannot advance further regarding their possible function, we believe that the comparison with other facilities destined for water runoff storage built in regions of similar ecology may result of some interest, and could provide quantified data regarding the behavior of the reservoirs and the situation of the water accumulated in them.

Facilities similar to the meroitic hafīrs have existed in different latitudes, as the tapkis in Nigeria, ponds in Eastern Africa, tanks in India (where in many cases fish as food source grow up), and also reservorios in South America. In some cases they were built in natural holes or where clay had been excavated for construction, usually just out of the area of small urban settlements. Some were covered with vegetation.

In Argentina, at the southern end of South America, there are interesting precedents related to human made reservoirs that collected rainwater for drinking both of livestock and human population (*). They were built from pre-Columbian times in the northwest of the country, in arid zones of the Provinces of Catamarca, La Rioja and Santiago del Estero. Most have ceased to be active with the implementing of deep wells, but some continue in service to this day as an alternative resource.

This region was incorporated to the Inca Empire in the late 15th century, a few decades before the Spanish conquest. The skill of the Inca engineers to design complex systems of drinkwater supply and storage is widely known. So, this could have been the source of the technology involved in these reservoirs.

This arid and hilly Argentine region has a climatological situation similar to that of the northeastern Sudan, with very scarce annual precipitation produced in very brief periods.

In the Ancasti Hills, desert zone to the west of Catamarca, with mountains of up to 2000 m high, and in the west of Santiago del Estero (Guasayán, Ambargasta and Sumampa Hills), the so-called “represas” were built. They could show different shapes, from rectangular to rounded, always with an entry faced in the direction of arrival of the water. They were partially excavated and with the excavated soil a perimetral wall was raised.

Rain waters falling down on rocky slopes slip at high speed and they infiltrate into minor proportion than those falling in flat zones.

In the Argentine northwest, with scarce granitic launderings, the water runoff over loess soils becomes an extremely cloudy stream, chocolate colored, loaded with suspended solids. Once arrived to the reservoir, these products are quickly spread over the whole liquid surface and then undergo a slow sedimentation forming a waterproofing soil.

The observation of these devices´ behaviour shows that the infiltration is usually more intense when a great water height is maintained. When the liquid level descends, during the dry season, the infiltration paradoxically also diminishes. A so called "asintotic" tendency allows that some liquid level could remain for several months.

The stored water was used for drinking both of human settlers and livestock, almost exclusively goats, the only domestic species that may last the scarcity of grassland.

In the Butana there exist bursts of igneous or schist-cristaline rocks. The water slips between them jumping over the stones at high speed and with minimal infiltration, creating occasional sudden streams that as the settlers know very well could become devastating.

We know that the base of the great hafīr of Musawwarat had been paired by grit and mud, covered by a layer of thin sand. This could have created a waterproofing of the surface, favoring the permanence of the liquid during longer periods.

The evaporation depends on temperature, moisture and wind speed. In the Butana the average temperature of December/January is 30.4°C, whereas in June it comes to 43° C.

It is worth noting that the high walls of the hafīrs could behave as a barrier against the wind, which in these regions constitute the principal evaporation agent.

The annual evaporation in Argentina ranges from 2000 to 2500 mm/year for small reservoirs in La Rioja, and about 3000 mm in Catamarca, that is to say similar records to those in the north of the Sudan: Deeker (1972), indicates for the Khashm el-Girba dam in Atbara an annual evaporation of 2.200 mm, and Kleinschroth (1986) quotes for the Butana 2600 mm/year.

The total height of the great hafīr of Musawwarat could have attained to 15 m, but we ignore what proportion of the same was actually filled. It is reasonable to think, nonetheless, that the mere existence of such high walls make think that great water volumes were expected, at least occasionally. Otherwise it seems unreasonable to have dedicated efforts and time to build structures able to store such water height.

Whereas in the arid region of Catamarca the average annual precipitations range between 100 and 450 mm, and in the Plains of La Rioja range between 200 and 500 mm/year, the scarce statistics indicate for Atbara little more than 50 mm/year, distributed in approximately 7 days a year, and for Hudeiba scarcely 36 mm/year. Nevertheless, theoretically it could be maintained an important liquid level up to the end of the period of "lean water" (lack of rains).

In the excavation of the Argentine reservoirs, the base was not smoothed completely, but some depressions were implemented, like extreme resource against the critical reduction of the liquid level. In such a circumstance water could concentrate on these depressions, and livestock (especially goats) could keep on drinking. Certainly if the rains were excessively scarce it was necessary to transfer the herds to some place with better water supply.

In other regions the reservoirs turned out to be the destination of urban garbage, causing the unavoidable contamination of the stored water. This was not the case of the Butana, as the hafīrs were relatively removed from the urban areas, but it could be argued that the high perimetral walls could have been also a practical way to prevent the access of livestock or settlers.

A disadvantage that can appear in the reservoirs is de-oxygenation, with proliferation of seaweed and development of smells proper of a body of stagnant water. In the cases of the Butana and the Argentine northwest it must be underlined the seasonal character of the water storage, that avoided the development of this adverse condition.

Permanent surface reservoirs in a hot climate are often subject to health hazards, while parasitic diseases are much less common around non-perennial devices.

In Argentina, the regular observation and long time experience have allowed to verify that these reservoirs could accomplish an unexpected function, because the stored water undergoes an improval in its quality, through completely natural reactions.

As we have noted, solids dragged by feeding water undertake a sedimentation in the reservoirs. The very thin slime particles sediment slowly along 30 to 60 days, so that the liquid becomes clarified. The coloidal particles (not visible at the naked eye) probably award to the residual water some turbidity, such it happens habitually in dams, but this does not affect its taste or smell.

Besides, water is not purified only in order to its physical clarification, that reduces the concentration of suspended matter, but a bacterial removal takes place also. It is the effect of technical studied "storage", which throughout the time produces a drop in the microbial population.

Water with relatively low microbial population exposed to permanent solar radiation can be rapidly and effectively decontaminated through the simple action of ultraviolet rays, developing a biological treatment with inhibition of pathogenic bacteria.

Biochemicals explain that certain molecules of the bacteria (riboflavines, porfirines, citocromes) absorb the quanta energy and get excited during less than a second, after which they re-send the energy to other molecules, causing photo-oxidations in residues of the proteins and in the nucleic acids bases: timine, citosine and uracil. In simpler words, the process prevent the cellular division, with lethal effects to the microorganisms.

Also it is possible to generate singlete oxygen (1O2), a highly reactive radical, that as an oxidizer can destroy the cell.

This way, the hafīrs could supply water with higher drinkability quality than that lifted from the Nile.

Moreover, the water body of the hafīrs presented a favorable environment for the development of aquatic vegetation. Species as papyrus and reeds are known as valuable helpers to improve the water quality. The potential for water purification of these plants has been widely verified, and in the technical literature they are recommended as simple and economic methods for drinking water treatment.

Perhaps some day further research could find proofs of the ancient presence of these plants in the meroitic hafīrs.

In the last decades, the resource of harvesting vegetable species has turned into an economic and practical way for the improval of the physical and chemical conditions in wastewater, particularly in the United States, and is known as “biological filtration”. It has been applied in Alexandria, Egypt, where common reed (Phragmites sp.), cattails (Typha sp.) and bulrush (Scirpus sp.) were planted in several wetlands basins to polish wastewater quality. They proved to be effective water clarifiers, assimilating and removing inorganic matter.

The ancient societies of the Nile Valley have demonstrated to develop empirical procedures, that sometimes anticipated the results of modern technology.

Certainly we are not postulating the application of sanitary skills with scientific criteria. Although it´s probable that the meroitic builders of the hafīrs didn´t know how such devices improved the water quality, we think that the experience of many years could allow them to become aware of the beneficial results effected on the water after certain storage period. The observation and the record of results could make possible the correction of mistakes in the design of the reservoirs and the linked structures. And their efficiency was going to remain demonstrated up to the point of continuing in use for many centuries after the sunset of the Meroitic civilization.

LITERATURE

(*) For the following references I am highly indebted to the late Eng. Carlos S. Carrique, a fellow of the Academia Argentina de Ingeniería (personal communication).

Abdalla, Abdelgadir M. (1984). “Summary of Discussion” on Meroitic Social Stratification. Meroitica 7, Berlin, p. 106.

CIR/WHO (1981). Small Community Water Supplies – Technology of small water supply system in developing countries.

Deekker, G. (1972). “A note on the Nile”. Water Resources Research 8 (4). pp. 818-928.

Hinkel, M. (1991). “Hafire im antiken Sudan”. ZÄS 118, pp. 32–48.

Hinkel, M. (1994). “The water reservoirs in Ancient Sudan”. In C. Bonnet (ed.), Études nubiennes, Vol.II, Genève, pp. 171–175.

Jahn, S. A. A. (1984). “Traditional water clarification methods using scientific observation to maximize efficiency”. Waterlines 2, pp. 27-28.

Kleinschroth, Adolf (1986). “Die Verwendung des hafirs im Meroitischen Reich”. BzS 1, pp. 79-96.

Miller, Robert L. (1990). “Ds-vessels, beer mugs, cirrhosis and casting slag”, GM 115, pp. 63-82.

Reimold, Robert J. and Margaret A. Mc Brien (1997). “Evaluating wetland treatment system for Alexandria, Egypt”, Waste Environment & Technology, Vol. 9 No. 3, pp. 29-34.

www.catamarca.gov.ar – Official web site of Catamarca Provincial Government, Argentina.

 

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