laureano_water catchment tunnels: qanat, foggara, falaj. an ecosystem vision.pdf

7/27/2019 Laureano_Water catchment tunnels: qanat, foggara, falaj. An ecosystem vision.pdf

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IWA Specialized Conference on Water&Wastewater 22-24 March 2012

Technologies in Ancient Civilizations Istanbul-Turkey

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MN-001

Water catchment tunnels: qanat, foggara, falaj. An ecosystem vision

P.Laureano

Ipogea, President of ITKI (International Traditional Knowledge Institute)

(Email:[email protected])

Abstract The paper highlights the characteristics of the water catchment tunnels generally

designated by the term qanat, which is commonly used in Iran, but they have different names and

are common in many geographic areas. The extreme difference in the functioning of the various

catchment tunnels is underlined. An emphasis is placed on the operating mode of a catchment

tunnel that highly depends on environmental and topographical circumstances as well as theseasons, the alterations in climatic conditions, and the long-term climatic cycles. Starting from a

critical assessment of the classical qanat functioning diagram the paper proposes a new

classification based on an ecosystem vision. The basic aspects of the catchment tunnels taken in

account are: the geomorphologic situation, the characteristics of the groundwater, the condition of

the soil and subsoil, the diversification of the tunnels components in a filtering segment and in a

conveying segment, and the exchanges and interactions with the atmosphere. The qanats are

constituted from the underground tunnel dug in light slope parallel to the ground and by the vertical

shafts. The tunnel does not dip into the aquifer, therefore, it drains the upper part, often through its

walls, as it crosses that part of the soil where the exchanges between deep waters and surface-

saturation waters are greatest.Continuous exchanges take place between the air above and below

ground, and one consequence of this circulation is the condensation of water in the soil when theground temperature is low enough. It is precisely in these exchanges and interactions that

catchment tunnels intervene. The airshaft and the filtering tunnel walls work to absorb the humidity

and to produce water. Between the extreme conditions - collecting water from a spring or from

ground sources, or producing water by exploiting contributions from the atmosphere (humidity,

occult precipitation, aerial sources) - lies the full range of catchment tunnels classified in four main

categories of ecosystem: mountain, foothill, plain, depression. Instead of regarding the catchment

tunnels as a homogeneous technique applied with different names in different countries the paper

shows the great differences in the functioning systems of the qanats within Iran itself and in the

various countries, and also of the change in the ways of operating of the same tunnel in different

seasons and climatic conditions. In the proposed vision the catchment tunnels are the product of

complex procedures, the point of arrival of diverse experiences developed in different areas andadapted to local geographical situations, so much so as to operate with various methods through

space and time.

Keywords ecosystem; qanat; water catchment tunnels; water condensation; water techniques

BACKGROUND

Making water flow where there is none, irrigating orchards, gardens and oases using gravity alone,without the need for pumps or lifting systems, long tunnels penetrate underground for miles, along
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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a gradient that is very nearly level, and whose constant slope is perfectly calculated to convey

water into the open air precisely where cultivations require. Tunnels of this sort have been in use

for three thousand years and are described with wonder by ancient authors. They appear in an

inscription of the seventh century BC traceable to the Assyrian king Sargon II; they are cited by theGreek historian Polybius in the second century BC (Histories, X, 28); they are described in Chinese

chronicles of the Han Dynasty reporting events of 53 BC (Wang, 1993) and they are present in

many agricultural manuals of the Arab tradition, from the monumental work of the first century AD

on Nabatean agriculture (Ibn Wahsiya,Al-filaha el Nabatiya), to the eleventh-century treatise of al-

Karagi (Karagi, Kitab inbat al miyah al hafiyya). They are generally designated by the term qanat,

which is commonly used in Iran, but they have different names and are common in many

geographic areas, from Asia, Europe and Africa to Oceania and America: qanatin Iraq and in Iran,

karez in China and along the Silk Road, falaj in Oman, surangan in India, khettara in Morocco,

foggara in Algeria, guettara and mlouka in Tunisia, madjirat, cimbras, minas and zanias in Spain,

cunicoli, ingruttatiand bottiniin Italy, mambo in Japan. Studies of catchment tunnels have become

increasingly numerous in the last four decades (Beaumont, 1971; Kobori, 1973; Kobori, 1976;

Sajjadi, 1982; Kobori, 1982; Bonine, 1987; Kobori, 1989; Kobori, 1990; Qanat Bibliography, 2000;

Briant, 2001; Kobori, 2005; Hermosilla, 2006; Tosi et al., 2007; Semsar Yazdi et al., 2010;

Hermosilla et al., 2011). Despite this growing interest, however, there is not yet, in general culture,

a univocal definition of these tunnels and a precise notion of how they work, so that commonly

used encyclopedias still define the way they are able to provide water as mysterious. This is due

to the fact that many publications use the same basic information, drawn from the work of Henry

Goblot, a French engineer who did his research in Iran. His book, Les qanat. Une technique

dacquisition de leau (Goblot, 1979), based on his doctoral dissertation of 1963, became the

source for most of the works that followed. The qanatdiagram he drew up, with a section view of a

tunnel, the geological strata and an indication of the aquifer, is reproduced in nearly every

publication (Figure 1). But this scheme is flawed and does not represent the complex reality of the

system. Xavier Planhol notes that Goblot received a good deal of criticism when defending his

dissertation (Planhol, 1992). This concerned the acceptance by Goblot of many clichs, false

impressions and considerations that led to arbitrary conclusions. Nevertheless, Goblots scheme

has been used in most subsequent studies, with the result that the analysis of a specific situation

has become a false generalization. Catchment tunnels, on the contrary, are complex inventions,

the culmination of many different experiences conducted in many different areas and adapted to

geographical conditions in such a way that their modes of operation differ in both space and time. It

is therefore impossible to understand catchment tunnels on the basis of observations made in one

place at one time. Account must be taken of the extreme difference in the functioning of the various

qanats in Iran alone, not to mention other countries, as well as of the way the operating mode of a


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single tunnel may change with the seasons, with alterations in climatic conditions, or in the course

of long-term cycles.

Figure 1. Classic catchment tunnel diagram according to Goblot. (A: position of thetunnel, section view; B: detail of the section view; C: overhead view; a: aquifer; b:

impermeable layer; c: horizontal tunnel; d: vertical shafts; e: surface channels; f:

settlement and/or irrigated area; g: filtering segment; h: conveying segment)(Goblot,

1979).

FUNCTIONALITY AND ENVIRONMENTAL CONDITIONS

The working of a catchment tunnel is highly dependent on environmental and topographical

circumstances. Different geographic variables thus determine different types of catchment tunnel.

In addition, a single catchment tunnel, working with water resources that are not apparent, as they

are the result of complex relationships with the ecosystem, often has different seasonal and

periodical water procurement modes. These are the main deficiencies of the commonly used

water-tunnel scheme proposed by Goblot. The greatest issues concern two basic aspects of

catchment tunnels: the characteristics of the groundwater, and the diversification of the tunnels

filtering and conveying components. Goblots diagram shows an important aquifer that breaks the

surface to produce open water downstream of the tunnel. In reality this case is rare, even in

tunnels in the mountains of Iran. More often, the layers containing water do not appear on the


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surface, even further downstream, and the tunnels are made expressly to catch water in areas

where it is not naturally present on the ground. In Goblots scheme, the tunnel bores through an

abundant aquifer with the part of its course that becomes conveying, while the other part takes on

filtering functions. Under this circumstance, however, the tunnel would flood with water underpressure, which would fill the vertical shafts to the highest level of the aquifer (Figure 2).

Figure 2. Author critical assessment of the Goblot classical catchment tunnel diagram. (A:

position of the tunnel, section view; B: detail of the section view; C: overhead view; a:

aquifer; b: impermeable layer; c: horizontal tunnel; d: vertical shafts; e: surface channels;

f: settlement and/or irrigated area; g: filtering segment; h: conveying segment; i: water

pressure; j: aquifer level; X: errors in the Goblots diagram).

The reality of catchment tunnels is quite different (Laureano, 1988). Water flows slowly in the

bottom of the tunnel, increasing its volume as it goes. The tunnel does not dip into the aquifer,

therefore, it drains the upper part, often through its walls, as it crosses that part of the soil where

the exchanges between deep waters and surface-saturation waters are greatest. To take account

of seasonal and climatic variations, the relationship between the conveying and filtering segments

variesin each single tunnel, and as a function of the tunnel type. Environmental contexts range

from humid ecosystems, which may hold varying amounts of water, to conditions of extreme

aridity. It should be noted that the terms humid and arid refer to the surface condition and

indicate the presence or absence of open water. The condition of the soil and subsoil may be

different. In deserts, in fact, water, which is minimal in the atmosphere and nonexistent on the


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surface, is present in the soil. And it is not always the water of deep aquifers. Under all conditions,

the atmospheric water cycle takes place not only in the open air, but underground as well. The

atmosphere in fact does not end where the air meets the soil, it continues in the deep layers.

Continuous exchanges take place between the air above and below ground, and one consequenceof this circulation is the condensation of water in the soil when the ground temperature is low

enough. It is precisely in these exchanges and interactions that catchment tunnels intervene

(Figure 3)(Laureano, 2005).

Figure 3. Water catchment tunnels hydro atmospheric cycle and water condensation inthe soil and in the sub-soil (1: atmospheric humidity; 2: condensation in the tunnels; 3:

water run-off; 4: humidity in the coltivations; 5: absorption of the humidity; 6: output of dry

air; a: aquifer; b: impermeable layer; c: horizontal tunnel; d: vertical shafts; e: surface

channels; f: settlement and/or irrigated area; j: aquifer level; k: fluctuations in aquifer

level). The air full of moisture of the palm grove is sucked out by the foggara in the

opposite direction to the water run-off; it condenses in the tunnel and comes out of the

shafts as dry air. During the night the temperature decreases and determines a further

moisture condensation on the soil surface that is absorbed by the shafts and the tunnel

(Laureano, 2005).

The tunnel absorbs and condenses the moisture coming from above, and sucks and condenses

the one from the bottom, helping to lift the water table. The cavity of the tunnel and of the vertical

shafts act as filtering gallery and condensation chamber. The vertical shafts regulate air changes

and maintain atmospheric pressure in the tunnel suitable to the water absorption and flow. When

the air is saturated, or nearly saturated, with moisture, small differences between interior and

exterior temperatures are enough to cause condensation. The hotter the air is, the more moisture it

can hold. In arid areas the differences in temperature between the surface and the subsoil, and the

wide variation in temperature between day and night, become decisive. Condensation is also


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facilitated by the capacity of water vapor to move, regardless of air movements, from points of

greater tension to points of lesser tension. Every shadow, every difference in temperature, humidity

or existing water share, further assists condensation. In the tunnels the filtering surfaces, the

stones and other asperities, the airshafts, all work together to manage the underground hydro-atmospheric cycle.

In the typological classification of catchment tunnels that follows, preference has been given to

geomorphologic characteristics (which profoundly affect the structure of the tunnel) over climatic

conditions, even though it is clear that situations of moisture or dryness at the surface affect how

water is procured. Generally speaking, in mountain and other moisture-rich locations, stress tends

to be placed on the capture and adduction of spring water. In very arid locations, where there is no

water source at the upper level, filtering along the tunnels course by capillary absorption of

superficial groundwater, of the underground flows of wadis or of atmospheric humidity, is more

prevalent. Between these extreme conditions - collecting water from a spring or from ground

sources, or producing water by exploiting contributions from the atmosphere (humidity, occult

precipitation, aerial sources) - lies the full range of catchment tunnels variations and possibilities

with respect to the four main categories of ecosystem: mountain, foothill, plain, depression.

CLASSIFICATION BY ECOSYSTEMS

Mountain Catchment Tunnels

Mountain catchment tunnels take advantage of more marked humid conditions (Figure 4). They are

located at high elevations, near the summit of mountains whose strata contain waters from

seasonal snows or glaciers. The tunnel touches on an underground aquifer, a mass of permeable

rock containing groundwater. The volume of the latter varies as a function of the season and the

moisture inputs of the slope, and the catchment tunnel itself governs its f luctuations. The mountain

water catchment tunnels irrigate small shelves of land and gentle slopes that have no perennial

streams from which water intakes can be organized, or areas in which streams are distant or at

lower elevations. Generally, mountain tunnels are not very long or deep, have a straight course,

quickly achieve their goal of capturing water, are dug in hard rocky soils and have a relatively small

number of broadly distanced vertical shafts. When they are very short they resemble the chambers

of artificial uptake sources; they are dug directly from the point of outlet and they may have no

vertical conduits at all. In these cases they are very like the wide range of water-management

techniques that extends from uptake caves to small catchment tunnels. The difference is due to the

fact that, generally, the latter serve to produce drinking water alone, whereas the catchment tunnel

is responsible for the production of more substantial resources for crops. The possibility of using


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the force of gravity to irrigate fields placed downstream of the tunnel is decisive for the latters

location. It always has a very precise topographical position between the mountain peak and the

slopes and terraces devoted to agriculture.

Figure 4.Mountain catchment tunnels. (A: position of the tunnel, section view; B: detail of

the section view; C: overhead view; a: aquifer; b: impermeable layer; c: horizontal tunnel;

d: vertical shafts; e: surface channels; f: settlement and/or irrigated area; j: aquifer level;

k: fluctuations in aquifer level; l: water influx from the slope; m: variations of the filtering

and conveying segments).

Foothill Catchment tunnels

Foothill catchment tunnels are located in the transition zones between rocky mountains and large

flood plains (Figure 5). Here sedimentary materials that are very conducive to infiltration can oftenbe found. The tunnels irrigate plains in the vicinity of high mountains, or wide valleys between

water-retaining mountain slopes. They are located in areas whose water supplies are produced by

the scale of the surrounding mountains, with volumes similar to those of mountain tunnels. Under

high-moisture conditions, sinking exploratory shafts to create the mother well, at the upper end of

the catchment tunnel, is the first step toward discovering where water is present. This has often led

to the mistaken believe that excavation proceeds from the highest elevation to the lowest, where

the tunnel surfaces. This is true, in the sense that the higher conduits and the mother well (test

well) are dug first, but the horizontal excavation is always conducted against the flow of water, in


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other words from the lower elevations to higher ones. This is because, in humid locations,

proceeding from above would entail working with the tunnel flooded. The tunnels path is

sometimes windy, due to the heterogeneity of the soil, and long, to intercept a larger part of the

aquifer. The vertical shafts are closely spaced and essential to the planning of the excavation. Thelevel of groundwater varies over time and may be partly determined by percolation in the slope,

runoff from the mountain and atmospheric inputs. Often the tunnels are located on the slopes of

valleys of torrential streams whose water flow is minimal or sporadic. The tunnel assures regular

flows at elevations higher than the streams course.

Figure 5. Foothill catchment tunnels. (A: position of the tunnel, section view; B: detail of

the section view; C: overhead view; a: aquifer; b: impermeable layer; c: horizontal tunnel

d: vertical shafts; e: surface channels; f: settlement and/or irrigated area; j: aquifer level;

k: fluctuations in aquifer level; l: water influx from the slope; m: variations of the filteringand conveying segments; n: contributions of rainfall or occult precipitation; o: absorption

by osmosis and capillarity, maintenance of the aquifer).

Foothills are where large areas of land suitable for major crops are most likely to be found. These

are often organized on broad terraces whose extent reflects the water flow of the tunnel. This, by

providing constant inputs, permits the creation of agriculture based on a continuous annual water

cycle and not on the intermittent or seasonal waters supplied directly by the environment. On the

lands along the gravitational path of the water from the tunnel to the fields and settlements, family-

based cooperative arrangements are organized that evolve into corporations based on water


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pacts. The foothill ecosystem offers a classic environment for extensive settlements based on

catchment tunnels. The morphology of the terrain encourages serial replication, along the slopes of

mountain ranges and the walls of plateaus, of a linear model structured by the catchment tunnel

from the higher elevations to the lower. In broad geographic contexts, such as the Iranian plateaus,multiple structures may give rise to systems of cities and complex regional state organisms.

Catchment tunnels of Plains and Riverbeds

The catchment tunnels of plains and riverbeds are located on broad alluvial deposits (Figure 6).

Here the water supply is less evident and is generally provided by surface resources. The courses

of the tunnels are longer and more ramified, often forming a system with many branches rather

than a single tunnel. Some are directed toward a hill or a slightly elevated part of the plain that is

able to conserve internal water resources. Others follow the bed of a dry river that may produce

sporadic floods. They may run parallel to the rivers banks or cross its course below ground,

drawing on the subsoil moisture it conveys. In arid conditions, because of the relative evenness of

the tunnels course, determining the site of the test well is much less important. Digging is begun at

the point of outflow, where irrigation is needed, and proceeds up the slope in an apparently

haphazard way. So the tunnels often follow irregular and ramified courses, as though their makers

had searched for the aquifer and then pursued it in different directions.

Aerial photos show that the tunnels follow the fossilized remains of dry hydrographic networks that

are not visible on the ground, within which, thanks to their filtering capacity, the tunnel produces

water. When the tunnels burrow through areas without water, in fact, they often run in a straight

line. A winding path, because it increases the extent of filtering surfaces intercepting the flow of

water beneath the slope, has a greater ability to extract water. The water supplies utilized are

several: surface groundwater, occult precipitation, and absorption by osmosis and capillary action

(Gauthier, 1928). Sometimes these supplies are associated with collateral works for the

replenishment of water in the soil layers they pass through, such as weirs interred in the riverbedor roadbed-torrents and other devices to direct flooding. Into this category fall some types of

coastal tunnels - those of Marsa Natrun in Egypt, for instance, which draw off the fresh surface

water that lies above denser, unusable layers saturated with salt. Smaller structures, cisterns

linked by subterranean channels, are very similar to the so-called qanat el roumi (Roman wells)

(Kobori, 1980), from which they may have evolved. In general, plain-type catchment tunnels are

long and ramified and supply major systems of settlement. Many thriving agricultural centers, large

capital cities and caravan destinations, first arose around this kind of tunnel and subsequently

expanded over the network of gardens and surface channels that are part of the system.


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Figure 6. Catchment tunnels of plains and riverbeds. (A: position of the tunnel, section

view; B: detail of the section view; C: overhead view; a: aquifer; b: impermeable layer; c:

horizontal tunnel; d: vertical shafts; e: surface channels; f: settlement and/or irrigated

area; j: aquifer level; k: fluctuations in aquifer level; l: water influx from the slope; m:

variations of the filtering and conveying segments; n: contributions of rainfall or occult

precipitation; o: absorption by osmosis and capillarity, maintenance of the aquifer; p:

contributions of humidity occult precipitation; q: hills; r: fossil riverbed).

Catchment tunnels of Depressions

Depression catchment tunnels are specific to arid and hyper-arid zones (Figure 7). A variant of the

previous type, they are associated with geomorphologic structures that are inherent to deserts: the

great salt depressions. Called sebkhas in the Sahara, these depressions are the remains of large

lakes that are now dry, and they lie at the center of fossil river systems that preserve small

underground micro-flows. Water moves in a capillary manner toward the depression; there it is

drawn to the surface by the high temperatures and evaporates, depositing its dissolved salts in the

soil, where they form a sterile crust. Catchment tunnels intervene in this natural hydrological

dynamic by intercepting the flows before they evaporate and producing open water that, by

exploiting the gradients around the depression, make it possible to create an oases and plant

palms and crops along its edges. This type of tunnel is typical of places of great historical and

cultural importance - places of the highest significance to human civilization in desert areas, such

as the Turpan depression in China, the city of Yazd in Iran and the Timimoun Sebkha in Algeria


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(Laureano, 1985). Depression catchment tunnels do not dip into the aquifer; where it exists, they

drain the top, without causing it to sink, absorbing amounts of water that are compatible with the

aquifers capacity for renewal. The area where groundwater accumulates resembles a large, rocky

sponge; it is fed by the micro-flows directed toward the sebkha, by the surfacing of deep aquiferscontaining persistent non-renewable geological water, and by atmospheric inputs.

Figure 7. Catchment tunnels of Depression. (A: position of the tunnel, section view; B:

detail of the section view; C: overhead view; a: aquifer; b: impermeable layer; c:

horizontal tunnel; d: vertical shafts; e: surface channels; f: settlement and/or irrigated

area; j: aquifer level; k: fluctuations in aquifer level; l: water influx from the slope; m:

variations of the filtering and conveying segments; o: absorption by osmosis and

capillarity, maintenance of the aquifer; p: contributions of humidity occult precipitation;

r: fossil riverbed; s: salt depression).

These are the same sources described by the medieval mathematician al-Karagi, who identifies

the tunnels waters as a combination of rainwater, primordial water and the subterranean

transformation of air into water. The interactions and exchanges between the different types of

water supply are crucial to the initiation of autocatalytic dynamics that reinforce virtuous water-

production cycles. Taken as a whole, the network of catchment tunnels in desert depressions

constitutes a vast system for the preservation of the aquifer. By ensuring moisture absorption by

the soil through exchanges with humidity in the air, it taps the upper part of the aquifer whilereplenishing, or regulating, its groundwater. It ensures harmonic conservation of the equilibrium of


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the ecosystem as a whole by placing its own components in just the right position in relation to

gravity and to environmental conditions. In this way it enables some of the most important habitat

systems in the world, the oasis, to flourish in situations of extreme environmental harshness

(Figure 8).

Figure 8. Catchment tunnel and oasis ecosystem. Water produced in the catchment

tunnel (A), which is visible thanks to the excavation shafts on the surface (B), runs

beneath the adobe habitat (C) and gathers further along in decantation tanks (D), useful

for drinking water, ablutions and for cooling the dwellings. Once conveyed in open-air

channels by means of the kesria (F), which serve to measure and distribute the water

flow, water irrigates the palm groove (E) subdivided into tilled parcels by low mud walls

(G) (Laureano, 2005).

REFERENCES

AA.VV. (2000). Qanat Bibliography. The First International Conference on Qanat, in Perse et Anglais, Yazd, Iran

Beaumont, P. (1971). Qanats systems in Iran. Bulletin of the international Association of Scientific Hydrology, 16, pp. 35-43

Bonine, M.E. (1987). Qanats, Irrigation, and the Morphology of Settlements , Proceedings of the Conference on Qanat System,s in the

Middle East Centre of Near and Middle Eastern Studies School of Oriental and African Studies, University of London, 18

March

Briant, P. (2001). Irrigation et drainage dans lAntiquit, qanats et canalisation souterraine en Iran, en gypte et en Grce, sminairetenue au Collge de France sous la direction de Pierre Briant, Thotm ditions, France

Goblot, H. (1979). Les Qanats, une technique d'acquisition de l'eau, Mouton, Paris

Gauthier, E.F. (1928). Le Sahara, Le Payot, Paris

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Kobori, I. (1976). Notes on Foggara in the Algerian Sahara. Bulletin of department of geography university of Tokyo, n. 8, pp. 41-55

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in the Arid Zone of the Old Continent, Report no. 1, Japan

Kobori, I. (1982). Case studies of foggara oases in the Algerian Sahara and Syria. Tokyo University Scientific Mission for the

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Polybius, Histoire de lempire perse, Fayard (1996) Paris, pp. 826-829, 1065-1068

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Semsar Yazdi, S.A.; Labbaf Khaneiki, M. (2010). Veins of Desert A review on the techinque of qanat/falaj/karez, First ed.Yazd, Iran(UNESCO)

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