Water resources in the Zayandeh Rud Basin in Iran have experienced enormous changes over the last centuries. Water use has been intensified substantially over the last 50 years. The changes are nicely reflected in the name Zayandeh Rud, which means 'the river that feeds itself'. It refers to the times when contributions from groundwater and tributaries increased the river flow in its journey to the outlet point. Nowadays, this picture has changed completely. From each drop of water that is released from the upstream-located reservoir, only half a drop reaches the main city Esfehan, and from this half drop nothing remains at the outlet point of the river.

It is clear that these changes will continue. Population growth is still on the rise, putting more emphasis on domestic water requirements. Industrial activities are becoming more profound, along with their associated water requirements. Food demands from the increased population will also put a higher claim on water, and agriculture (already the biggest consumer of water) might come under severe stress.

On top of these stressors are the uncertain impacts of climate change and climate variability and the need for adaptation strategies. Unfortunately, climate change issues have not been sufficiently considered by the basin's policy makers. At the national level a few activities have been initiated by the National Environmental Organization. We hope the present research work helps in developing a more structured policy with regards to the impacts of climate change and variability.

This chapter first illustrates the characteristics of the basin. Next we will describe some novel approaches, in the context of Iran. A framework is used to assess the impact of climate change and to explore adaptation strategies to minimize the possible negative effects of climate change. We will demonstrate our approach for the Zayandeh Rud Basin in the centre of Iran. Since agriculture plays such an important

© CAB International 2004. Climate Change in Contrasting River Basins

Fig. 6.1. Location of Zayandeh Rud Basin in Iran.

role in the basin, we will concentrate on this, but will do this in the context of other water consumers.

Physical characteristics

The Zayandeh Rud Basin is located in the central part of Iran, with geographical coordinates of approximately 33° North and 53° East (Fig. 6.1). The area of the basin is about 42,000 km2. Esfahan province constitutes 88% of the Zayandeh Rud Basin. The rest of the basin is located in Bakhtiyary and Yazd provinces. The city of Esfahan is the capital of Esfahan province, which is one of the oldest cities in the world with about 2 million inhabitants.

The river itself has provided the basis for important economic activities for centuries, including the growth and establishment of Esfahan as the former capital city of Persia. The region has been able to support a long tradition of irrigated agriculture in order to meet the domestic needs of the population and industrial demands.

However, the agriculture sector, being the main water consumer using more than 80% of the available water resources, is heavily under pressure. Numerous factors, including the continued growth of the urban population, the development of new agriculture lands and the rapid increase in industrial demands, have caused water shortages over the last half a century. To overcome these problems, a number of trans-basin water projects were realized and exploited over the last decades. There is, however, still insufficient water to irrigate the total irrigable area. It has also resulted in a reduction of water quality of the Zayandeh Rud, especially downstream of the city of Esfahan. Deterioration of water quality causes problems for the ecosystem of the river and for Gaw Khuny swamp, the final outflow point of the river.

The Zayandeh Rud Basin consists of seven sub-basins, namely Plasjan, Shur Dehghan, Khoshk Rud, Morghab, Zar Cheshmeh, Rahimi and Gaw Khuny swamp. The upper catchment of the basin is part of the Zagros Mountains, with high altitudes and ample precipitation. The general slope direction of the upper basin is west to east and the elevation varies between 1000 m and 3600 m. The upper basin is of paramount importance in terms of water resources, since almost all water that is used in the basin originates from this mountainous area. The natural vegetation covering the lower basin is sparse, as precipitation downstream is very low (50-200 mm/year) and erratic.

Elevation has a significant effect on climatological conditions and its spatial and temporal variation. Precipitation in the basin is mainly driven by the Mediterranean rainfall system, which enters from the north-west of the country. The western mountains of the basin and their direction induce substantial rainfall. Rainfall reduces rapidly in the basin from west to east, ranging from 1400 mm on the most upper portion of the catchment (mostly as snow) to 700 mm in the intermediate part. The amount of rainfall reduces to less than 100 mm at the downstream Gaw Khuny swamp. Potential evapotranspiration ranges from 1450 mm to 2800 mm.

The dominant land use types in the basin are pasture and uncultivated land. The Morghab sub-basin is very important for agriculture and the main irrigation networks are located here. Most of the forests and rain-fed areas are located in the Plasjan sub-basin. So, in terms of economic activities these two sub-basins are the most crucial ones in the Zayandeh Rud Basin.

Water resources

Water resources are highly regulated by man-made infrastructural systems. Numerous water projects have been constructed, are under construction or are under study. The Chadegan Dam is the main water reservoir with a capacity of 1450 X 106 m3 and has been exploited since 1971. After the construction of the dam, 90,000 ha were added to the traditional network. At present about 297,000 ha of irrigated land is surface water and groundwater dependent.

Even after the construction of the dam, insufficient water is available and water scarcity is common in the basin. Inter-basin transfer is a common practice to alleviate the severe water shortage. For example, water is diverted from the Karoon Basin to Zayandeh Rud by two tunnels. These tunnels divert 300-400 X 106 m3 water/year. In spite of this huge project, the basin is still under threat and two additional tunnels are under construction. A third tunnel will divert water from Karoon River and Tunnel No. 2, the Lenjan tunnel, from Dez River upper catchment (Anonymous, 1993). These two new tunnels, with a total capacity of 425 X 106 m3, are expected to be completed in 2004 and 2008, respectively. Another tunnel, the 75 km Behesh Abad is under study, but investment costs will be huge. The total diversion of water from this tunnel is estimated to be 7 00-1000 X 106 m3. It would join the Zayandeh Rud River downstream of the Chadegan Dam. These projects will play a crucial role in minimizing water deficiency in the basin and the possible negative impacts of climate changes.

Alongside these efforts to alleviate water scarcity by transferring water from outside the basin to the Zayandeh Rud, there are projects diverting water from the basin to neighbouring cities. The first phase of the Yazd project has been operational since 2002, diverting 42 X 106 m3 water/year out of the basin. In the second phase of the project the amount of diverted water will increase to 78 X 106 m3/year. Kashan and Shahr Kurd diversion projects with a total capacity of 24 X 106 m3/year are under construction.

Groundwater resources play a crucial role in storage and regulation of water resources. Wells and qanats, the traditional Iranian system to extract groundwater, are the main means to extract groundwater. Presently, about 20,138 deep and semi-deep wells (total 3224 X 106 m3/year), 1726 qanats (313 X 106 m3/year) and 1613 springs (82 X 106 m3/year) are extracting a total of 3619 X 106 m3 groundwater/year.

Comparing surface water extraction (1245 X 106 m3) with that of groundwater (3619 X 106 m3) reveals the significant role of groundwater resources for the study area. Overall, about 90% of the total water resources in the study area are controlled (Anonymous, 1993).

The Esfahan Water Authority (EWA) studies the basin groundwater budget every year. The year 2000 study revealed that all the plains have a high rate of overdraft. One of the main reasons is that during 2000 the basin suffered from a severe drought. But also the long-term trend demonstrates an overdraft and declining groundwater tables. Return flows from the irrigation systems are the main source for groundwater recharge.

The Zayandeh Rud River has for centuries provided the basis for important economic activities. Looking at water consumption, these activities can be categorized into three sectors: agriculture, industry and domestic. Agriculture is the dominant water user, consuming more than 80% of the river yield. But this amount is still insufficient to irrigate the total irrigable area. It is estimated that water consumption per hectare varies from 10,000 to 14,000 m3.

The total area of irrigation systems is estimated to be about 180,000 ha, with Neku Abad, Abshar, Borkhar and Rudasht the major irrigation systems in the basin. The Neku Abad and Abshar irrigation systems were constructed in 1970. The designed command area of these systems is about 90,000 ha. Borkhar and Rudash, with a total command area of 83,000 ha, have been under cultivation since 1997 and parts of the systems are still under construction. There are irrigation systems that are expected to be exploited in the near future (e.g. Keron irrigation system).

Huge industrial complexes are located in the basin. The most important ones are Esfahan Steel Mill, Mobarekeh Steel Complex and a number of textile factories that consume about 100 X 106 km3 water/year. The population of Esfahan city is about 2 million, with a domestic water use of about 80 m3/year per capita. In terms of servicing the ecosystem, 70 X 106 km3 is the minimum water requirement for preserving the downstream located Gaw Khuny swamp (see also the next section).

Agriculture and environment

The dominant crops in the basin are: cereal (wheat, barley, rice, maize and sorghum), forage (lucerne, clover, sainfoin and maize), pulse (bean, lentil and chickpea), and

Table 6.1. Main agricultural crops in the basin and average and maximum obtainable yields.


Average yield

Maximum yield

Crop type




















industrial crops (cotton, sugarbeet, safflower and potatoes). Wheat, rice, barley and potatoes are the main staple crops in the basin and a major source of caloric intake for people and livestock (Table 6.1). The yields provided in the table for these staple crops are average values and some farms in the basin have higher performances.

The Zayandeh Rud River and the Gaw Khuny swamp are two important natural ecosystems in the basin. The Gaw Khuni swamp is the final outflow point of the river and is an important wetland recognized by the Convention of Ramsar (1975). The mean area of the swamp is about 43,000 ha, but varies annually as a result of variation in total inflows. During wet years, the depth of the swamp reaches 1.5 m, but normally the depth is between 0.3 and 0.6 m. Quantity and quality of the river are highly dependent on releases from the dam and on the numerous water diversions along the 350 km reach of the river to the swamp. Furthermore, the water quality of the river and swamp is affected by the return flows from the upstream demand sites. The wildlife of the swamp depends on the water depth. The lowest critical depth for vital activity is about 15 cm, which can be maintained with 2.2 m3/s inflow to the swamp (~75 X 106 km3 water/year). A more favourable depth is 30 cm, which requires an inflow of about 4.5 m3/s (140 X 106 km3 water/year). This depth is optimal to support fish, birds, plants and small mammals (Moeinian, 2000).

Main sources of river pollution can be categorized into three groups: domestic effluents, industrial and agricultural return flows (Anonymous, 1993). Eighteen stations observe the limnological parameters of the Zayandeh Rud river and are maintained by the Esfahan Water Authority and Esfahan Environment Organization. The river water quality can be categorized in four segments. The first segment is from the Chadegan dam up to the upstream of Esfahan (180 km). For this part, main sources of pollutants are agricultural return flows. In the second part, significant changes can be seen on water quality (180 to 220 km). Return flows from industry, especially textile factories, and Esfahan water treatment plants are the main sources of pollutants. The third segment is from 220 to 270 km, where some decay of pollutants takes place. After this segment, agricultural return flows are again the main sources of pollutants that deteriorate water quality, where the Segzy drain is one of the main culprits.

The largest source of domestic pollutant of the Zayandeh Rud River is the effluent of Esfahan city. The wastewater treatment plant of the southern part of Esfahan is in the vicinity of the river. This system, which was designed for 800,000 people, consists of three separate units. The total volume of effluents is some 126,400 m3/day, causing serious environmental problems in the river ecosystem, especially during low flows. Although water treatment purification of the system reduces the organic discharge of the wastewater, purification efficiency is only about 85% and needs improvement. Downstream of Esfahan city, domestic pollutants are less relevant and river water quality is more affected by agricultural drainage.

Agricultural drainages contain soluble salts, insecticides and herbicides residues, leached chemical fertilizers and heavy metals. The Zayandeh Rud Basin has three main agricultural drainage systems, referred to as Steel Mill, Rudasht and Segzi drains. These drains enter the river at distances from the regulating dam of 111, 254 and 296 km, respectively. The Steel Mill drain is an open channel to control the groundwater level of the Zarrin Shahr region located at the western part of Esfahan city. It receives high amounts of return flows from agricultural lands and conveys them to the river with an approximate flow rate of 14,400 m3/day. It also receives part of the outflow from the Esfahan Steel Mill water treatment plant. The Rudasht drain collects drainage water of the Rudasht region and discharges it in the river at 5808 m3/day. The Segzi drain is the largest and most important drain of the basin and the discharge of the drain exceeds the river flow during some periods, particularly in summer and autumn. Mean drain discharge is about 28,700 m3/day and salinity levels are too high to be used for irrigation.

Socio-economic and institutional characteristics

From 1966 to 1991, the population in the basin increased from 1.1 to 3.0 million. According to the 1996 census, the population of the entire basin was 3.9 million, of which 2.9 million people live in the urban areas (34 cities) and 1 million are rural residents (1212 villages). Most of the residential areas and almost 82% of the basin's population (cities as well as villages) are located along the Zayandeh Rud River. About 76% of the rural population lives in the Morghab sub-basin. The population of Esfahan and its suburbs is about 2 million and their drinking water is directly supplied by the Zayandeh Rud River. The government has taken positive measures to control the population and its growth rate has started to decrease since 1991 and is estimated to be about 2% for 2000.

The main institution responsible for domestic water exploitation and distribution is Esfahan Water Authority (EWA), which is supervised by the Ministry of Energy. The water distribution up to the tertiary irrigation channel level of the irrigation system is also the responsibility of the Ministry of Energy. Supervision of the exploitation from groundwater resources is included in their mandate as well.

The Esfahan Agriculture Authority, which is supervised by the Jehad-Keshavarzy (Agriculture) Ministry, coordinates the water distribution in tertiary and lower level channel networks. Watershed management and small-scale water projects (e.g. groundwater artificial recharge) are some of the related water duties of the Esfahan Agriculture Authority. Environmental issues in the basin are controlled by the Esfahan Environment Authority The Iranian Environment Organization is an independent organization, which is directly under the supervision of the Iranian President.

Non-governmental organizations (NGOs) have been activated recently in Esfahan, focusing on Zayandeh Rud River and the river ecosystem. In addition to this, several NGOs have invested in minor irrigation systems and maintenance of the systems.



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