A. Kowsar
Ahang Kowsar is Senior Research Scientist at the Research Institute of Forests and Rang elands, Shiraz. Iran. Note: This article is adapted from a voluntary contribution to the Tenth World Forestry Congress.
Ironically, water; the most precious element in arid zones and the shortage of which is an important cause of desertification, is also a main agent of erosion. Consequently, water management is often the key to many aspects of desertification control. However; capital-intensive and sophisticated engineering solutions are impractical under the prevailing socio-economic conditions in most deserts. Simpler; less expensive yet effective approaches to water management have therefore to be found This article describes the test of an integrated approach based on floodwater spreading in southern Iran.
More than 90 percent of the land area in Iran is classified as arid or semi-arid. The mean annual precipitation of the 87 million ha of the mountainous regions and 77.8 million ha of the plains areas are 365 mm and 115 mm, respectively (Anon., 1984). Approximately one-half of Iran's water supply comes from surface waters, with most of the remainder coming from ground water aquifers which are significantly overdrawn. Therefore, drought is an ever present threat to most of Iran.
Ironically, periods of drought are often punctuated by flood-producing downpours that devastate the drought stricken people and their livestock. However, if harnessed, these floods can bring life back to the desert. It is therefore essential to upgrade the status of floods from a curse to a blessing and to ameliorate drought conditions with the wise use of floodwaters.
Floodwater spreading is an easy method of harnessing the sediment, which is usually wasted, and the nutrient-rich waters for a number of important uses: to satisfy the water requirements of annual and perennial crops, range plants, shrubs and trees, either immediately or over time by using surface reservoirs and aquifers; to recharge aquifers to prevent the intrusion of salt water into water-bearing strata; to stabilize drifting sands through precipitation of the suspended load; to grade land on sloping and eroded surfaces; to reduce gully erosion and control downstream flooding; and to leach saline soils.
Moreover, in addition to being economically feasible and environmentally sound, floodwater spreading may be undertaken with local traditional skills and experience, enabling desert communities to become self-sufficient in water, food, forage and energy. It is hoped that the following description of a floodwater spreading pilot effort in Iran will result in its widespread replication, thereby helping to resolve conflicts between economy and ecology.
The pilot area is a 6000 ha sandy expanse located on the debris cone of the Bisheh Zard River in the Gareh Bygone Plain. The site faces southwest, has a 0.6 percent slope and ranges from 1120 to 1160 m above sea-level. The climate is Mediterranean, with hot summers and cold winters. The mean annual precipitation is about 150 mm, 90 percent of which occurs between October and April. The mean annual evapotranspiration is estimated to be 2860 mm (Surface Waters Authority, 1976). Besides the Bisheh Zard River, two other ephemeral streams, the Tchah Qootch River and the Gehr Ab River, flow into the area on average twice in the winter and once in the summer.
Carex stenophylla is the most common plant species in the Plain. Scattered bushes of Ziziphus nummularia (Burm. f.) and Pteropyrum aucheri are found by the stream banks and in the rivulets and depressions. Atriplex leucoclada, Artemisia sieberi and Astragalus glaucacanthos occupy the eroded, silty clay soils on the eastern margin of the debris cone; while Helianthemum salicifolium (L.), Stipagrostis plumosa (L.), Cynodon dactylon (L.), Alhagi camelorum and a few annual medicks (Medicago spp.) are prevalent on the debris cone.
Eight floodwater spreading systems, ranging from 25 to 365 ha in area with a total coverage of 1365 ha, were designed and constructed between 1983 and 1987 on the intermediate zone of the debris cone. The procedures used are a modification of those outlined by Quilty (1972). These systems serve as sedimentation basins and infiltration ponds for the artificial recharge of ground water; and also as experimental plots for investigating range improvement, moving sand stabilization, afforestation, plant water requirements, etc.
Flood water spreading into sedimentation basins in 1986. Note the two-year-old eucalypts
After being grown in perforated polyethylene bags, nine-month-old seedlings of Eucalyptus camaldulensis Dehnh., E. microtheca, Acacia cyanophylla, A. salicina and A. victoriae were planted in the first floodwater spreading system in February and March 1983. Actual planting was done adjacent to the upslope toe of the banks of the channels, along the waterline of the diversion canal and near the inside toe of the end banks. The planting lines were ripped to a depth of 35 cm using bulldozer-mounted rippers. The seedlings were planted at 3 m intervals, usually in a single row. Flood irrigation, carried out on most of the planting sites in January and March 1983, eliminated the need for watering seedlings immediately after transplanting. The seedlings were protected from browsing for nine months. Fertilization, pest management activities or other types of after care were not undertaken. The unexpected survival and growth of E. camaldulensis during the first growing season encouraged its planting in successive years, not only near the banks but in 3x3 m spacing between them as well. To date, more than 60000 seedlings of this species have been planted.
Transformation of a desolate, sandy expanse into a verdant horizon is the most obvious result of the floodwater spreading pilot effort. A clear space in a dust bowl is proof of its effectiveness in stabilizing drifting sands. The expansion of irrigated fields in what was previously a water short area is convincing evidence of the effectiveness of artificial recharging of ground water. The gradual return of wildlife to the area bears witness to the presence of feed and shelter.
Finally, the inward migration by those inhabitants who had left the Gareh Bygone Plain is an auspicious sign. These phenomena are discussed in slightly more detail below.
From January 1983 through February 1988 there were 21 floods of varying intensity and duration. It is estimated that a total of 38 million m3 of water were diverted by the floodwater spreading systems and that, of these, upwards of 25 million m3 were directed to recharging the ground water while the rest were used in initial wetting of the alluvium or were consumed through evapotranspiration. Under unimproved conditions, less than 10 percent of the precipitation finds its way into the ground water aquifers. Assuming uniform distribution of water over the 1365 ha pilot area, the annual amount of water received by most of the living organisms would have been more than doubled.
Provision of irrigation water for 514 ha of existing farms and the creation of 492 ha of new, irrigated farmland appears to be the most tangible economic outcome of the floodwater spreading pilot effort. The average yield of barley (used as a feed grain ) on 650 ha of the pilot area was 1400 kg per hectare, more than twice that of a control area. A coincidental rise in commodity prices has greatly increased the income of farmers in the area and should provide strong incentives for replication of this method. In fact, the combined income from the barley and more than one tonne per hectare of stubble was 2.3 times the cost per hectare of constructing the floodwater spreading system. Moreover, in the deluge of 1986, it is estimated that the water-impounding capacity of the floodwater spreading system avoided damages equivalent to ten times its construction cost.
Survival of the tree species five years after planting ranged from 37 percent for A. cyanophylla to 79 percent for E. camaldulensis. The subzero temperatures in January 1984 killed the A. cyanophylla to the ground; however, stem sprouts on the surviving roots have grown into very large bushes, some with a crown volume of 100 m3. Although the survival and growth of E. microtheca, A. salicina and A. victoriae have been satisfactory, those of E. camaldulensis have been outstanding. Of the 627 seedlings planted neat channel No. 6 of the first sites of the system - which were not irrigated at all before planting nor for 11 months thereafter - only 34 percent succumbed to drought. Although these seedlings grew very little during the first year, they have been competing successfully ever since with those that were flood irrigated once or twice at the time of planting. Apparently, the estimated 150 mm of precipitation in the fall of 1982 and the winter of 1983 provided enough reserve to satisfy the survival requirements of the non-irrigated seedlings. The cumulative six-year height growth for E. camaldulensis ranges from 8 to 16 m, with the tallest trees being located near the conveyor-spreader channel and the shortest ones in a position that is inundated only once a year. The DBH ranges from 12 to 25 cm for these six-year-old trees. The estimated yield of the five-year-old plantations was calculated at 12.7 m3 of main stems per hectare.
Deposition of silts, clays and organic matter on sands has transformed the surfaces into a cohesive, wind-resistant material. Provision of a better growth medium, containing more nutrients and having a higher water-holding capacity, has helped spontaneous proliferation of existing vegetation and the invasion of new plant species. Although the importance of the eucalypt shelter-belts in reducing wind erosion should not be slighted, the moving sands from the bands between the tree rows, which had not been covered by the suspended load, point to the very significant role played by the floodwater spreading in stabilization.
The prevailing climate in the treated area is distinctly milder than that of the surrounding desert and many birds and mammals have found refuge there. The return of the houbara bustards (Chlamidotis undulata) and gazelles (Gazella subgutturosa) to their previous haunt may be interpreted as an indication of the recovery of a degraded habitat.
Although an accurate evaluation of the fodder yield of the system is difficult because of the continuing grazing of livestock, an estimate may be made. The annual dry matter production was estimated to be 20 to 50 kg per hectare prior to project implementation; in 1987 this figure ranged from 240 to 1950 kg per hectare, with an average of 515 kg per hectare. This figure was validated when 1877 sheep and 1760 goats were grazed on a 500 ha tract for a duration of 45 days in November and December 1987.
Honeybees swarm A. salicina from October through March when other plants usually frequented by the bees are not in flower. This represents the possibility of revolutionizing the beekeeping industry in southern Iran.
Floods and drought are realities of desert life. Floodwaters, rather than compounding the problem, should be used to ameliorate the effects of drought. Where potential aquifers are available, they should be recharged, while food, feed and fuelwood are produced on the land above them. Floodwater spreading systems have the potential to make a significant impact on arid-zone life.
Anon. 1984. Tentative water balance in Iran. Ab, 3.
Kassas, M. 1987. Drought and desertification. Land Use Policy, 4(4): 389-400.
Kowsar, A. 1989. Floodwater spreading for desertification control: an integrated approach. An Iranian contribution to the Plan of Action to Combat Desertification Tehran, Research Institute of Forests and Rangelands.
Kowsar, A. 1990. Artificial recharge of groundwater for small - scale water development in rural areas: a case-study. Paper presented at the Int. Symp. Devel Small-Scale Water Resour. in Rural Areas, 21-25 May 1990, Khon Kaen, Thailand.
Mabutt, J.A. 1987. Implementation of the Plan of Action to Combat Desertification: progress since UNCOD Land Use Policy, 4(4): 371-388
Quilty, J.A. 1972. Soil conservation structures for marginal arable areas - gap absorption and gap spreader banks. J. Soil Conserv. Serv . (NSW), 23(3): 116-130.
Surface Waters Authority. 1976. Rainfall and evaporation maps of Iran. Tehran, Ministry of Power. (in Farsi)
Tolba, M.K. 1987. Ten years after UNCOD. Land Use Policy, 4(4): 363-370.
