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Runoff (floodwater) farming and rural water supply in arid lands
Applied Geography (1986), 6, 5-1I
Runoff (floodwater) farming and rural water supply in arid lands D . D . Gilbertson Department of Prehistory and Archaeology, University of Sheffield, Sheffield S/0 2TN, UK
Introduction This note provides a brief introduction to a series of 'theme papers' in Applied Geography which describe recent research on runoff or floodwater farming and water supply in rural areas in arid lands (Bruins et al. 1986 ; Gale and Hunt 1986 ; Nabhan 1986a,b ; Brunner and Haefner 1986 ; Hulme 1986 ; and Davies 1986) . The various terms which have been used to describe the irrigation and farming of marginal arid lands by capturing and concentrating surface runoff are discussed in Bruins et al . (1986) . In the past the term `floodwater farming' has been widely adopted following its use by the geologist Kirk Bryan (1929) to describe the surfacewater harvesting and farming techniques of the Indians of Arizona and adjacent states . In many arid lands the surface water used is often derived largely from a few storms, hence the term floodwater farming is particularly appropriate when the centres of cultivation are in valleys or basins on upland plateaux . Approximately one-half of the world's nations live partly or wholly in arid or semiarid lands . Le Houerou and Lundholm (1976) estimate that 3-5 per cent of the lands in the world's arid zone, which lie beyond those that may be cultivated reliably using conventional dryland farming methods, might be brought under cultivation using the techniques of runoff farming . The significance of these figures in a hungry world is self-evident . Runoff or floodwater farming and 'wall technologies' There are three main interrelated facets to the subject of runoff farming-physiographic, agricultural-ecological, and socio/cultural/economic/political . The first is most readily studied, best known and understood (see Boers and Ben Asher 1982 ; Yair 1983) ; the last group is more intractable and least understood . At its most basic, this practice represents an entire land management system which is based upon concentrating and tapping surface runoff by the ingenious use of a 'wall technology', often combined with the clearance over a large area of obstacles to overland flow (e .g . cobbles and boulders) on the contributing slopes of the catchment(s) . Unfortunately, descriptive figures, plates and text are an inadequate substitute for a field inspection of the transformation a 'simple' technology can make in the otherwise desolate and barren, arid wilderness, In much of North Africa and the Middle East the starting point for studies of floodwater farming lies on the alluvium infilling wadi floors, although alluvial fans, gullies, and basins on the adjacent plateaux, are also important . Plate I shows a series of check-dams or 'cross-wadi walls' in southern Jordan which are successfully ensuring the supply of soil moisture and soil necessary to sustain a crop of olives in a 0143-6228/86/010005-07 $03 .00 -_ 1986 Butterworth & Co (Publishers) Ltd
6
Runoff (floodwater) farming and rurul water supply in and lands
Plate 1 . Check-dams- cross-wadi walls' which trap floodwater and sediments in a wadi floor in southern Jordan (photo D . D . Gilbertson 1982) . very dry location . Hillsiope terracing is complimenting the valley-floor cultivation in this example . In more arid environments, valleyside walls may be designed to send surface flow- rapidly down the valleyside to valley or basin floors where cultivation is concentrated . The valley- and basin-floor check-dams impede the flow of water derived from the occasional storms, which may provide very heavy downpours . The ponded water is allowed to soak into the alluvial valley infills . Crops and/or forage grasses are sown, germinate, or are revitalized in the wet soils and sediments, Later, the Quaternary infill acts as a below-ground reservoir which can be exploited at drier times of the year by deeper-rooting species and tapped by pits or wells for human and animal consumption . In many areas of the world these valley-floor check-dams may be only 0 . 5 m high comprising two or three lines of cobbles or boulders (e .g . see Plate 1 and Herold 1970 ; Evenari et al. 1971) . Agriculture based on overland flow and floodwater did and can survive and prosper in very hazardous arid environments . For example, in many locations, simple cobble-built barrages, 0 . 5-1 . 5 km long, have successfully controlled and concentrated the huge, potentially damaging floods which sweep down arid-zone valleys (see Evenari et at . 1971, 1982 ; Jones and Barker 1980, 1983, 1984 ; Barker and Jones 1981, 1982 ; Gilbertson et al . 1984 ; Brunner and Haefner 1986) . Sophisticated systems of sluices, diversions and overflows, and distribution networks may be associated with the larger structures to better exploit the water from the occasional storm . In some of the more arid situations, hillslopes and plateaux are extensively tapped for storm-generated overland flow by simply constructed, long walls (Plate 2) which `snake' across the low-angle slopes of plateaux or wadi sides . These walls intercept, concentrate and direct the large quantities of storm-generated overland flow which would otherwise be lost rapidly from the agricultural system . The walls may guide the
D . D . Gilbertson
7
Plate 2 . Plateau (hamada) wall intercepting, concentrating and guiding storm runoff from shallow, plateau catchments to wadi-side and wadi-floor floodwater farms in the Libyan predesert near Beni Ulid . The wall is feature 'D' in Fig . 2 of Gale and Hunt 1986 (photo D . D . Gilbertson 1980) . storm runoff into shallow upland basins, waterproofed chambers . caves or other storage hollows, or via a series of walls or gullies, down the wadi-side wall onto the valley floor . In this manner, a large quantity of water is concentrated and directed into relatively small areas which are cultivated, used as special grazing areas, or which serve as reservoirs for human or animal needs . In reality this picture is an over-simplification . The walls and wall systems may individually or in various combinations meet a variety of interrelated objectives (Gilbertson et at . 1984) : 1 . to control the capture, storage and redistribution of surface water for human or animal consumption or for irrigation via surface ponding or channel irrigation ; 2 . to control fluvial erosion, sediment entrainment, transportation and deposition ; 3 . to control the movements of animals, either as pens or enclosures for domesticates or excluding unwanted wild animals, or for hunting wild animals ; 4 . to delineate areas of different land use ; 5 . they may also be by-products of stone clearance, intended to improve the potential for surface runoff ; 6 . they may define parcels of land control or ownership .
Past successes It is one of the sad ironies of the modern world that people go hungry in 'barren desert' lands which, hundreds or thousands of years ago, yielded rich harvests as a result of the use of the ingenious techniques of floodwater farming . The agricultural significance of ancient 'wall technologies' has been recorded in the literature for many years (e .g . Barth 1857 ; Bandelier 1892) . The evidence of 'long-lived', intensive
8
Runoff (Jloodtcater) ibrming and rival water supply in arid lands
and extensive `ancient' farming practices, based on collecting, guiding and ponding storm water caith simple walls is well documented from arid South and Central America, the arid Southwest of North America, across North Africa and the Middle East leg . see Farrington and Park 1978 ; Gilbertson et al . 1984 : Bruins er at. 1986 ; Brunner and Haefner 1986 ; Nabhan 1986a,b ; and references therein) . Much of the (and cultivated by runoff farming supported more than subsistence agriculture ; for example . the pre-desert and Mediterranean coastal strip inland of the Gulf of Sirte in Romano-Libyan times grew and exported vast quantities of grain, olives and other products to the Roman Empire to the North . In this North African example, successful agriculture employing floodwater farming lasted several hundred years in Romano-Libyan times and probably for a comparable period in the early Islamic period . Brunner and Haefner (1986) describe a floodwater runoff system in the arid Yemen which lasted for at least two thousand years . At various locations in Jordan (Plate 1 ; Kirkbride 1966 ; Helms 1981 ; Gilbertson and Kennedy 1986) and in the Negev (Evenari er a! . 1971 ; Lev=y 1981, 1983) the practice of runoff farming has been known for several more thousand years . The antiquity of these systems post-dates the more major climatic changes which characterized the early and middle Holocene in many arid lands, especially around the Sahara (see Beadle 1974 ; Rognon 1976 ; Street and Grove 1976, 1979 ; Nicholson and Flohn 1980) . Activity over such long periods of time (no doubt with short interruptions and breaks) indicates that the runoff and floodwater farmers must have witnessed and coped with all sorts of environmental fluctuations, changes and extreme events . These data suggest the essential soundness and resilience of the water-gathering, agricultural and cultural systems which constituted runoff farming in many arid lands . It is apparent from the distribution of these developments that the essential principles of runoff farming have been devised independently by local people, in many different parts of the world, at many different times . The success of any particular scheme %kill have depended upon the skill with which the basic hydrological and agricultural principles (which are set out in the following articles) were adapted to the particular local situation, in both its physiographic and socio/economic/ political context . The importance of an `eye for the country', detailed local knowledge, locally-adapted cultivars and management practices does not seem to have appealed to the majority of `European' colonists and managers who subsequently acquired authority in many of the areas . For example, examination of the history of runoff farming in the Sonoran desert described by Nabhan (1986a,b) suggests the sorry, recent history of decline and decay in this particular farming system . Sadly, as a result, the principles and local modifications which enabled floodwater farming to succeed for so long, have been forgotten or overlooked, the numbers of people with detailed knowledge of their local landscape have greatly declined, and emphasis has been placed by managers and developers on larger, 'conventional' irrigation schemes . By way of contrast, the advantages and problems of such development schemes are explored in the two studies from arid Sudan discussed in this `theme series' by Hulme (1986) and Davies (1986) . Nevertheless, the obvious attractions of runoff farming as one component of attempts to re-establish a satisfactory subsistence agriculture in arid lands are beginning to re-assert themselves . These attractions include the employment of local people, on their own land, working in their own interests ; the building or rehabilitation of locally-adapted farming/water control schemes ; the (re)application of ideas that are already indigenous to the region ; the use of cheap, abundant and local raw materials-rocks and rubble, and the partial satisfaction of the reasonable demand
D . D . Gilbertson
9
of burgeoning populations to own and farm their own land . In addition there are the further benefits of the lack of a necessity for capital investment, high technology, imported fuels, or large numbers of overseas advisers, technicians and 'foreign' work camps . The future At present there is every reason to hope that the introduction and rehabilitation of ancient floodwater farming systems, in appropriate physiographic situations, may help sustain useful extra production of arable, citrus or forage crops . At the very least, the check-dams will help to contain certain problems of soil erosion and improve forage crops . However plateaux and hillslope walls and surface treatments may have different results . Nevertheless, it must be realized that although floodwater farming can bring under-utilized ground into useful production, the exact details of the particular variations in methods and crops necessary for successful intensive or extensive developments need to be evaluated in each prospective location . In times past, the necessary knowledge and `eye for the country' would have been available from the fund of experience in the local population of many arid lands . Fortunately, in Arizona, the older Papago Indians of the Sonoran Desert can indicate such crucial local details of site preference, crop mixes, crop husbandry, pastoral policies and maintenance strategies (Nabhan 1979, 1986a,b) . Elsewhere this information is lost and must be estimated from environmental surveys, archaeological surveys, field trials and experiments (see Evenari et al . 1971, 1982) . Areas of past development and potential future development may be identified on conventional aerial photography (when available) or in certain situations from conventional or `image-analysed' LANDSAT imagery (Dorsett et al. 1984) . It is clear that in the 'modern' world, runoff farming in the more marginal situations is not without risk . It may be necessary to be prepared to support the subsistence farmer with 'back-up' food and water supplies in the inevitable 'bad' years . Larger projects intended to generate surpluses will certainly require such support as well as specialist advice as to which of the many variations of runoff farming practices (see Bruins et al. 1986) are most suitable in a particular circumstance . The emphases on the longevity, widespread distribution and resilience of floodwater farming schemes must not disguise the unhappy fact that on many occasions in the past, such schemes have been abandoned . Nowadays attention is directed increasingly to the significance of cultural, social, economic, political or organizational causes of failure or poor performance in these marginal situations (see Davies 1986 ; Hulme 1986) . However, it still also remains the case that in many arid lands there is an inadequate knowledge of the relationships between floodwater runoff and farming systems and questions concerning soil erosion, soil deterioration, salinization, overgrazing and critical environmental fluctuations (e .g . see Barker et al . 1983 ; Gilbertson et al . 1984) . There is a pressing need for more field surveys, field trials, experimental farms and eventually demonstration farms to explore further the concepts, and publicize the usefulness of these ingenious runoff-based schemes, which may yet supply, at minimal costs, water for people, animals and crops in some of the more marginal of arid lands on the earth . Acknowledgements The author is indebted to the following who have enabled him to investigate flood-
10
Runoff (floodwater) farming and rural water supply in and lands
water farming systems in Arizona, Jordan and The Socialist People's Libyan Arab Jamahiriya : The Laboratory of Tree Ring Research and Department of Geological Sciences, University of Arizona, Tucson ; Dr D . L . Kennedy ; The British School of History and Archaeology at Amman ; and the UNESCO Libyan Valleys Project of the Universities of Manchester and Sheffield and The Department of Antiquities in Tripoli under its Director, Dr Abdullah Shaiboub . References Bandelier, A . F . (1892) Final report of investigations among the Indians of the Southwestern United States carried on mainly in the years 1880 and 1885 . Papers of the Archaeological Institute of America, American Series /II and IV. Cambridge : John Wilson & Son . Barker, G . W . W . and Jones, G . D . B . (1981) The UNESCO Libyan Valleys Survey, 1980 . Libyan Studies 12, 9-48 . Barker, G . W . W . and Jones, G . D . B . (1982) The UNESCO Libyan Valleys Survey 19791981 : palaeo-economy and environmental archaeology in the pre-desert . Libyan Studies 13, 1-34 . Barker, G . W . W ., Gilbertson, D . D ., Griffin, C . M ., Haves, P . P . and Jones, D . A . (1983) The UNESCO Libyan Valleys Survey V : sedimentary properties of Holocene wadi floor and plateau deposits in Tripolitania, North-West Libya . Libyan Studies 14, 69-85 . Barth, H . (1857) Travels and discoveries in North and Central Africa . London : Longman . Beadle, L . L . (1974) The inland waters of tropical Africa. London : Longnian . Boers, Th . M . and Ben Asher, J . (1982) A review of rainwater harvesting . Agricultural Water Management 5, 145-158 . Bruins, H . J ., Evenari, M . and Nessler, U . (1986) Rainwater-harvesting agriculture for food production in arid zones : the challenge of the African famine . Applied Geography 6, 13-32 . Brunner, U . and Haefner, H . (1986) The successful floodwater farming systems of the Sabeans, Yemen Arab Republic . Geographical Review 6, 77-86 . Bryan, K . (1929) Floodwater farming . Geographical Review 19 (3), 444-456 . Davies, H . J . R . (1986) The human factor in development : some lessons from rural Sudan? Applied Geography 6, 107-121 . Dorsett, J . E ., Gilbertson, D . D ., Hunt, C . O . and Barker, G . W . W . (1984) The UNESCO Libyan Valleys Survey VIII : Image analysis of Landsat Satellite data for archaeological and environmental survey . Libyan Studies 15, 71-80 . Evenari, Nt ., Shannon, L . and Tadmor, N . (1971, 1982) The hegev-the challenge of a desert (2nd enlarged edition, 1982) . Cambridge, Mass . : Harvard University Press . Farrington, I . S . and Park, C . C . (1978) Hydraulic engineering and irrigation agriculture in the Moche Valley, Peru : c. AD 1250-1532 . Journal of Archaeological Science 5, 255-268 . Gale, S . J . and Hunt, C . O . (1986) The hydrological characteristics of a floodwater farming system . Applied Geography 6, 33-42 . Gilbertson, D . D ., Hayes, P . P ., Barker, G . W . W . and Hunt, C . O . (1984) The UNESCO Libyan Valleys Survey VII : an interim classification and functional analysis of ancient wall technology and land use . Libyan Studies 15, 45-70 . Gilbertson, D . D . and Kennedy, D . L . (1986) An archaeological reconnaissance of ancient flood-water farms in the Jordanian desert, north of Azraq Oasis . Annals of the Department of Antiquities of Jordan (in press) . Helms, S . (1981) Jawa: lost city of the Black Desert. London : Methuen . Herold, L . C . (1970) Trincheras and physical environment along the Rio Gavalan, Chihuahua, Mexico . Denver, Col . : University of Denver Publications in Geography, Technical Paper No . 65-1 . Hulme, fvt . (1986) The adaptability of a rural water supply system to extreme rainfall anomalies in Central Sudan . Applied Geography 6, 89-105 . Jones, G . D . B . and Barker, G . W . W . (1980) Libyan Valleys Survey . Libyan Studies 11, 11-36 .
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Jones, G . D . B . and Barker, G . W . W . (1983) The UNESCO Libyan Valleys Survey : the 1981 Season . Libyan Studies 14, 39-68 . Jones, G . D . B . and Barker, G . W . W . (1984) The UNESCO Libyan Valleys Survey VI : Investigations of a Romano-Libyan farm, Part 1 . Libyan Studies 15, 1-44 . Kirkbride, D . (1966) Five seasons at the pre-pottery Neolithic village of Beidha in Jordan . Palestine Exploration Quarterly 78, 8-72 . Le Houi rou, H . N . and Lundholm, B . (1976) Complimentary activities for the improvement of the economy and the environment in marginal drylands . In Can desert encroachment be stopped? A study with emphasis on Africa. Ecological Bulletin 24 (A . Rapp, H . N . Houeron and B . Lundholm, eds), pp . 217-229 . Stockholm . Levy, T . E . (1981) Chaloclithic settlement and subsistence in the northern Negev desert, Israel . Unpublished PhD dissertation, University of Sheffield . Levy, T . E . (1983) The emergence of specialised pastoralism in the southern Levant . World Archaeology 15, 15-36 . Nabhan, G . P . (1979) The ecology of floodwater farming in arid southwestern North America . Agro-Ecosystems 5, 245-255, Nabhan, G . P . (1986a) Papago Indian desert agriculture and water control in the Sonoran Desert, 1697-1934 . Applied Geography 6, 43-59 . Nabhan, G . P . (1986b) 'Ak-cin 'arroyo mouth' and the environmental setting of Papago Indian fields in the Sonoran Desert . Applied Geography 6, 61-75 . Nicholson, S . and Flohn, H . (1980) African environmental and climatic changes and the general circulation in late Pleistocene and Holocene . Climatic Change 2, 313-348 . Rognon, P . (1976) Essai d'interpretation des variations climatiques au Sahara depuis 40,000 ans . Revue Geographie Physiques et Dynamiques 18, 251-282 . Street, F . A . and Grove, A . T . (1976) Environmental and climatic implications of late Quaternary take-level fluctuations in Africa . ,Vature261, 285-290 . Street, F . A . and Grove, A . T . (1979) Global maps of lake-level fluctuation since 30,000 years BP . Quaternary Research 12, 83-118 . Yair, A . (1983) Hillstone hydrology of water harvesting and areal distribution of some ancient agricultural systems in the northern Negev desert . Journal of Arid Environments 6, 283-301(Revised manuscript received 30 March 1985)
Runoff (floodwater) farming and rural water supply in arid lands D . D . Gilbertson Department of Prehistory and Archaeology, University of Sheffield, Sheffield S/0 2TN, UK
Introduction This note provides a brief introduction to a series of 'theme papers' in Applied Geography which describe recent research on runoff or floodwater farming and water supply in rural areas in arid lands (Bruins et al. 1986 ; Gale and Hunt 1986 ; Nabhan 1986a,b ; Brunner and Haefner 1986 ; Hulme 1986 ; and Davies 1986) . The various terms which have been used to describe the irrigation and farming of marginal arid lands by capturing and concentrating surface runoff are discussed in Bruins et al . (1986) . In the past the term `floodwater farming' has been widely adopted following its use by the geologist Kirk Bryan (1929) to describe the surfacewater harvesting and farming techniques of the Indians of Arizona and adjacent states . In many arid lands the surface water used is often derived largely from a few storms, hence the term floodwater farming is particularly appropriate when the centres of cultivation are in valleys or basins on upland plateaux . Approximately one-half of the world's nations live partly or wholly in arid or semiarid lands . Le Houerou and Lundholm (1976) estimate that 3-5 per cent of the lands in the world's arid zone, which lie beyond those that may be cultivated reliably using conventional dryland farming methods, might be brought under cultivation using the techniques of runoff farming . The significance of these figures in a hungry world is self-evident . Runoff or floodwater farming and 'wall technologies' There are three main interrelated facets to the subject of runoff farming-physiographic, agricultural-ecological, and socio/cultural/economic/political . The first is most readily studied, best known and understood (see Boers and Ben Asher 1982 ; Yair 1983) ; the last group is more intractable and least understood . At its most basic, this practice represents an entire land management system which is based upon concentrating and tapping surface runoff by the ingenious use of a 'wall technology', often combined with the clearance over a large area of obstacles to overland flow (e .g . cobbles and boulders) on the contributing slopes of the catchment(s) . Unfortunately, descriptive figures, plates and text are an inadequate substitute for a field inspection of the transformation a 'simple' technology can make in the otherwise desolate and barren, arid wilderness, In much of North Africa and the Middle East the starting point for studies of floodwater farming lies on the alluvium infilling wadi floors, although alluvial fans, gullies, and basins on the adjacent plateaux, are also important . Plate I shows a series of check-dams or 'cross-wadi walls' in southern Jordan which are successfully ensuring the supply of soil moisture and soil necessary to sustain a crop of olives in a 0143-6228/86/010005-07 $03 .00 -_ 1986 Butterworth & Co (Publishers) Ltd
6
Runoff (floodwater) farming and rurul water supply in and lands
Plate 1 . Check-dams- cross-wadi walls' which trap floodwater and sediments in a wadi floor in southern Jordan (photo D . D . Gilbertson 1982) . very dry location . Hillsiope terracing is complimenting the valley-floor cultivation in this example . In more arid environments, valleyside walls may be designed to send surface flow- rapidly down the valleyside to valley or basin floors where cultivation is concentrated . The valley- and basin-floor check-dams impede the flow of water derived from the occasional storms, which may provide very heavy downpours . The ponded water is allowed to soak into the alluvial valley infills . Crops and/or forage grasses are sown, germinate, or are revitalized in the wet soils and sediments, Later, the Quaternary infill acts as a below-ground reservoir which can be exploited at drier times of the year by deeper-rooting species and tapped by pits or wells for human and animal consumption . In many areas of the world these valley-floor check-dams may be only 0 . 5 m high comprising two or three lines of cobbles or boulders (e .g . see Plate 1 and Herold 1970 ; Evenari et al. 1971) . Agriculture based on overland flow and floodwater did and can survive and prosper in very hazardous arid environments . For example, in many locations, simple cobble-built barrages, 0 . 5-1 . 5 km long, have successfully controlled and concentrated the huge, potentially damaging floods which sweep down arid-zone valleys (see Evenari et at . 1971, 1982 ; Jones and Barker 1980, 1983, 1984 ; Barker and Jones 1981, 1982 ; Gilbertson et al . 1984 ; Brunner and Haefner 1986) . Sophisticated systems of sluices, diversions and overflows, and distribution networks may be associated with the larger structures to better exploit the water from the occasional storm . In some of the more arid situations, hillslopes and plateaux are extensively tapped for storm-generated overland flow by simply constructed, long walls (Plate 2) which `snake' across the low-angle slopes of plateaux or wadi sides . These walls intercept, concentrate and direct the large quantities of storm-generated overland flow which would otherwise be lost rapidly from the agricultural system . The walls may guide the
D . D . Gilbertson
7
Plate 2 . Plateau (hamada) wall intercepting, concentrating and guiding storm runoff from shallow, plateau catchments to wadi-side and wadi-floor floodwater farms in the Libyan predesert near Beni Ulid . The wall is feature 'D' in Fig . 2 of Gale and Hunt 1986 (photo D . D . Gilbertson 1980) . storm runoff into shallow upland basins, waterproofed chambers . caves or other storage hollows, or via a series of walls or gullies, down the wadi-side wall onto the valley floor . In this manner, a large quantity of water is concentrated and directed into relatively small areas which are cultivated, used as special grazing areas, or which serve as reservoirs for human or animal needs . In reality this picture is an over-simplification . The walls and wall systems may individually or in various combinations meet a variety of interrelated objectives (Gilbertson et at . 1984) : 1 . to control the capture, storage and redistribution of surface water for human or animal consumption or for irrigation via surface ponding or channel irrigation ; 2 . to control fluvial erosion, sediment entrainment, transportation and deposition ; 3 . to control the movements of animals, either as pens or enclosures for domesticates or excluding unwanted wild animals, or for hunting wild animals ; 4 . to delineate areas of different land use ; 5 . they may also be by-products of stone clearance, intended to improve the potential for surface runoff ; 6 . they may define parcels of land control or ownership .
Past successes It is one of the sad ironies of the modern world that people go hungry in 'barren desert' lands which, hundreds or thousands of years ago, yielded rich harvests as a result of the use of the ingenious techniques of floodwater farming . The agricultural significance of ancient 'wall technologies' has been recorded in the literature for many years (e .g . Barth 1857 ; Bandelier 1892) . The evidence of 'long-lived', intensive
8
Runoff (Jloodtcater) ibrming and rival water supply in arid lands
and extensive `ancient' farming practices, based on collecting, guiding and ponding storm water caith simple walls is well documented from arid South and Central America, the arid Southwest of North America, across North Africa and the Middle East leg . see Farrington and Park 1978 ; Gilbertson et al . 1984 : Bruins er at. 1986 ; Brunner and Haefner 1986 ; Nabhan 1986a,b ; and references therein) . Much of the (and cultivated by runoff farming supported more than subsistence agriculture ; for example . the pre-desert and Mediterranean coastal strip inland of the Gulf of Sirte in Romano-Libyan times grew and exported vast quantities of grain, olives and other products to the Roman Empire to the North . In this North African example, successful agriculture employing floodwater farming lasted several hundred years in Romano-Libyan times and probably for a comparable period in the early Islamic period . Brunner and Haefner (1986) describe a floodwater runoff system in the arid Yemen which lasted for at least two thousand years . At various locations in Jordan (Plate 1 ; Kirkbride 1966 ; Helms 1981 ; Gilbertson and Kennedy 1986) and in the Negev (Evenari er a! . 1971 ; Lev=y 1981, 1983) the practice of runoff farming has been known for several more thousand years . The antiquity of these systems post-dates the more major climatic changes which characterized the early and middle Holocene in many arid lands, especially around the Sahara (see Beadle 1974 ; Rognon 1976 ; Street and Grove 1976, 1979 ; Nicholson and Flohn 1980) . Activity over such long periods of time (no doubt with short interruptions and breaks) indicates that the runoff and floodwater farmers must have witnessed and coped with all sorts of environmental fluctuations, changes and extreme events . These data suggest the essential soundness and resilience of the water-gathering, agricultural and cultural systems which constituted runoff farming in many arid lands . It is apparent from the distribution of these developments that the essential principles of runoff farming have been devised independently by local people, in many different parts of the world, at many different times . The success of any particular scheme %kill have depended upon the skill with which the basic hydrological and agricultural principles (which are set out in the following articles) were adapted to the particular local situation, in both its physiographic and socio/economic/ political context . The importance of an `eye for the country', detailed local knowledge, locally-adapted cultivars and management practices does not seem to have appealed to the majority of `European' colonists and managers who subsequently acquired authority in many of the areas . For example, examination of the history of runoff farming in the Sonoran desert described by Nabhan (1986a,b) suggests the sorry, recent history of decline and decay in this particular farming system . Sadly, as a result, the principles and local modifications which enabled floodwater farming to succeed for so long, have been forgotten or overlooked, the numbers of people with detailed knowledge of their local landscape have greatly declined, and emphasis has been placed by managers and developers on larger, 'conventional' irrigation schemes . By way of contrast, the advantages and problems of such development schemes are explored in the two studies from arid Sudan discussed in this `theme series' by Hulme (1986) and Davies (1986) . Nevertheless, the obvious attractions of runoff farming as one component of attempts to re-establish a satisfactory subsistence agriculture in arid lands are beginning to re-assert themselves . These attractions include the employment of local people, on their own land, working in their own interests ; the building or rehabilitation of locally-adapted farming/water control schemes ; the (re)application of ideas that are already indigenous to the region ; the use of cheap, abundant and local raw materials-rocks and rubble, and the partial satisfaction of the reasonable demand
D . D . Gilbertson
9
of burgeoning populations to own and farm their own land . In addition there are the further benefits of the lack of a necessity for capital investment, high technology, imported fuels, or large numbers of overseas advisers, technicians and 'foreign' work camps . The future At present there is every reason to hope that the introduction and rehabilitation of ancient floodwater farming systems, in appropriate physiographic situations, may help sustain useful extra production of arable, citrus or forage crops . At the very least, the check-dams will help to contain certain problems of soil erosion and improve forage crops . However plateaux and hillslope walls and surface treatments may have different results . Nevertheless, it must be realized that although floodwater farming can bring under-utilized ground into useful production, the exact details of the particular variations in methods and crops necessary for successful intensive or extensive developments need to be evaluated in each prospective location . In times past, the necessary knowledge and `eye for the country' would have been available from the fund of experience in the local population of many arid lands . Fortunately, in Arizona, the older Papago Indians of the Sonoran Desert can indicate such crucial local details of site preference, crop mixes, crop husbandry, pastoral policies and maintenance strategies (Nabhan 1979, 1986a,b) . Elsewhere this information is lost and must be estimated from environmental surveys, archaeological surveys, field trials and experiments (see Evenari et al . 1971, 1982) . Areas of past development and potential future development may be identified on conventional aerial photography (when available) or in certain situations from conventional or `image-analysed' LANDSAT imagery (Dorsett et al. 1984) . It is clear that in the 'modern' world, runoff farming in the more marginal situations is not without risk . It may be necessary to be prepared to support the subsistence farmer with 'back-up' food and water supplies in the inevitable 'bad' years . Larger projects intended to generate surpluses will certainly require such support as well as specialist advice as to which of the many variations of runoff farming practices (see Bruins et al. 1986) are most suitable in a particular circumstance . The emphases on the longevity, widespread distribution and resilience of floodwater farming schemes must not disguise the unhappy fact that on many occasions in the past, such schemes have been abandoned . Nowadays attention is directed increasingly to the significance of cultural, social, economic, political or organizational causes of failure or poor performance in these marginal situations (see Davies 1986 ; Hulme 1986) . However, it still also remains the case that in many arid lands there is an inadequate knowledge of the relationships between floodwater runoff and farming systems and questions concerning soil erosion, soil deterioration, salinization, overgrazing and critical environmental fluctuations (e .g . see Barker et al . 1983 ; Gilbertson et al . 1984) . There is a pressing need for more field surveys, field trials, experimental farms and eventually demonstration farms to explore further the concepts, and publicize the usefulness of these ingenious runoff-based schemes, which may yet supply, at minimal costs, water for people, animals and crops in some of the more marginal of arid lands on the earth . Acknowledgements The author is indebted to the following who have enabled him to investigate flood-
10
Runoff (floodwater) farming and rural water supply in and lands
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