A New Classification of Traditional Water Harvesting Systems
A consideration of current classifications of traditional water systems in North Africa and the Middle East led Fekri Hassan to develop an alternative classification.
The proposed system is based on an initial categorization of water harvesting systems on the basis of the source of water (rainfall, surface runoff, river flood discharge, wadi flow, groundwater, and air humidity). Water harvesting systems are then classified on the basis of the nature of -
Modification of the earth surface into subtractive features creating depressions (e.g.,
Reservoirs, pits, holes, conduits, cisterns, wells) and additive features creating elevated landforms (bunds, ridges, mounds, walls, dams). Combinations of these elements create multiplex water harvesting systems (negarim, foggaras, terracing).
The following diagrams illustrate the logic behind the new classification:
The main terms used in discussing traditional water harvesting include:
Bunds.--Permeable Ridges constructed from earth or stones
Catchment Area.--Area from which water is collected (see Micro-Catchment)
Contour.--Imaginary line connecting points of the same elevation in a landscape.
Infiltration.--Water percolating into the ground.
Runoff.--Water movement from rainfall downslope.
Runoff capture.--percentage of rainfall captured by runoff.
Ranging from a few percentages to 50%.
Micro-catchment.--A small catchment area from a few square meters to around 1000 square meters.
Permeable.--A medium that allows water to flow through it.
Soil.-- The top part of the ground produced under the effect of vegetation.
Slope.-- The inclination of the surface of the ground measured as percent or angle. Slopes are characterized as gentle or steep.
Storage.--Accumulation of water in the ground through infiltration, in natural depressions, or in artificially created reservoirs, pools or cisterns.
Wadi bed.--floor of wadi channel.
I. Direct Rainwater Harvesting
Rainwater harvesting techniques collect the rainfall before it enters the soil, i.e. as surface runoff.
The collection and concentration of rainfall and its use for the irrigation of crops, pastures, trees, for livestock consump-tion and household purposes is called rainwater harvesting.
Roof & Courtyard Rain Water Harvesting
Water is collected from the rooftop of a house (and some times a courtyard). It is then transported though a pipe to be filtered and stored for domestic use. In Greece this technique is called Impluvium.
II. Surface Runoff Water Harvesting
This group of techniques depends on the harvesting of surface runoff water from a small catchment area ranging from a few square meters to around 1000 square meters.
Ponds, small reservoirs (Birak, ??? pl. Birka, ???? sing)
Water accumulates in artificial depressions from direct rainfall and surface runoff to form water pools and ponds. The amount of water and its persistence in the pond depends on the amount and seasonality of rainfall as well as the spacing of rain storms. It also depends on the compaction, pavement or smoothing of the catchment area, which can be artificially enhanced. It also depends on reducing infiltration by sealing the bottom of the pond and lining the pond with stones and plaster. They range in capacity from 1000 to 500,000 cu.m.
In Syria, a Birka is a stone built reservoir.
Semicircular & trapezoidal bunds (permeable structures)
Crescent shaped earth bunds, usually constructed in staggered rows.
Bunds arranged downslope in straight lines to slow surface runoff and increase infiltration.
Crescent shaped earth ridges constructed down-slope from trees to increase water harvesting and infiltration in the ground.
Circular ridges from earth constructed to enhance water retention and infiltration.
Tree retention ring
The construction of a wall around a tree in order to retain moisture and occasional precipitation
Terracing (small-scale and large-scale)
Reshaping the slope by a series of more or less flat steps.
Earthen low ridges arranged to create artificial basins.
Linear ridges constructed along the contour lines at intervals of between 5 and 20 meters.
Contour bench terraces
Often on very steep slopes, the terraces are supported by stone walls. Common in Yemen for growing coffee and qat as well as trees and field crops.
Small stone mounds were used by the Nabateans to enhance surface water runoff by as much as 25%. They are called by the Bedouins Tuleilat el-'Anab (vineyard hillocks) and might have been used for supporting the cultivation of vineyards (Issar 1990, 181). The system is perhaps analogous to the more substantial "Kroum" of the Egyptian coast.
Small (0.3-2 m in diameter), deep pits (5-15 m). A dyke may be constructed downslope from the pit.
Artificial tells (Kerma, ???? sing, kroum, ???? pl. Egypt )
Artificial mounds of earth constructed to allow rainwater to flow into farming area and subterranean cisterns. Used on the coastal area of Egypt in Roman times to irrigate vine and olive orchards. (Photos F. Hassan, Maryut, Egypt)
Used on gentle slopes, one bare strip is used as a catchment while the strip downslope from it is used for growing crops, mostly field crops.
Negarim (small runoff basins)
Small (5-10 m in width and 10-25 m in length) runoff basins, rectangular, elongated or diamond-shaped surrounded by low earth bunds. Suitable for tree crops.
Hillside conduit system
Excavation of water runnels to harvest water and direct it to where it is needed.
A canal to transfer water running along a hillside. A wall may be built to form the outer wall of the aqueduct.
Hillside runoff system (Saliba) Sylaba, sailaba
Water flowing downhill is directed to flat-lying fields by small conduits before it joins the wadi. A spillway may be used to drain excess water for use downstream.
Water tank, Hafi (the Sudan), Kuruf (Karif sing. Yemen)
Large earthen or stone built reservoir dug into the ground downslope from a wadi to collect water.
Stone-lined water tank, Mawajel (Yemen)
Tanks for water storage, often circular with plastered floors for domestic use (Yemen).
Pond with a settling tank
A settling tank is situated so that solid particles in the water are allowed to settle before water enters the pond.
Small subsurface water containers with a capacity ranging from 10 to 500 cu. m. They are often rock-cut. Varieties include pit cisterns, jar cisterns, or built stone cisterns. They receive water from rainfall, water drip in caves, groundwater, or runoff. A settling area may be used to remove solid particles in water.
Underground cistern for rainwater harvesting
Cistern with a settling basin
A settling basin is constructed to prevent solid particles from entering the cistern.
Roofed cistern, Siqayat (sing. Siqaya), Niqb, Greek-type Cistern
Roofed tanks or cisterns below ground with roof above ground.
Abar Romani (Syria)
Cisterns excavated in bedrock, Syria.
Domed Cistern, Kumbet (Iran)
A cistern covered with a dome-like structure, Iran.
Constructed on the coast of Egypt during WWII by the British troops to store water (Photo F. Hassan, Dab'a, Egypt)