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E AR C
E AR C
Sustainable Irrigation and Water Management in the Zayandeh Rud Basin, Iran
Iranian Agricultural Engineering Research Institute
Esfahan Agricultural Research Center
International Water Management Institute
Research Report No. 3
An Overview of the Hydrology of the
Zayandeh Rud Basin
H. Murray-Rust , H. Sally,
H.R. Salemi, A. Mamanpoush
E AR C
E AR C
I A ERI
I A ERI
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H. Murray-Rust, H. Sally, H.R. Salemi, A. Mamanpoush. 2000. An Overview of the
Hydrology of the Zayandeh Rud Basin, Esfahan Province, Iran. IAERI-IWMI Research
Reports 3.
Keywords: Salinity, simulation model, Iran, agro-hydrology, irrigation
H. Murray-Rust, International Water Management Institute
H. Sally, International Water Management Institute
H.R. Salemi, Esfahan Agricultural Research Center
A. R. Mamanpoush, Esfahan Agricultural Research Center
The IAERI-EARC-IWMI collaborative project is a multi-year program of research,
training and information dissemination fully funded by the Government of the Islamic
Republic of Iran that commenced in 1998. The main purpose of the project is to foster
integrated approaches to managing water resources at basin, irrigation system and farm
levels, and thereby contribute to promoting and sustaining agriculture in the country.
The project is currently using the Zayendeh Rud basin in Esfahan province as a pilot
study site. This research report series is intended as a means of sharing the results and
findings of the project with a view to obtaining critical feedback and suggestions that
will lead to strengthening the project outputs. Comments should be addressed to:
Iranian Agricultural Engineering Research Institute (IAERI)
PO Box 31585-845, Karaj, Iran.
Phone: +98-261-241116, fax: +98-261-226277
e-mail: maryam.sal@neda.net
Esfahan Agricultural Research Center (EARC)
PO Box 81785-19, Esfahan, Iran
Phone: +98-31-757201-2, fax: +98-31-759007
e-mail: agresor@cc.iut.ac.ir
International Water Management Institute (IWMI)
PO Box 2075, Colombo, Sri Lanka
Phone: +94-1-867404, fax +94-1-866854
e-mail: iwmi@cgiar.org
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An Overview of the Hydrology of the
Zayandeh Rud Basin, Esfahan Province, Iran
H. Murray-Rust, H. Sally, H.R. Salemi, A. Mamanpoush
Abstract
This paper provides an overview of the hydrology and water use in the Zayandeh Rud
basin based on the data available over the 11-year period 1988-1998. The inflows into
Chadegan reservoir, the releases from the reservoir, and the extractions along the river
for irrigation and other purposes are considered, and a rapid water balance of the
basin is performed.
Inflows to the Chadegan reservoir, which serves to collect and regulate the runoff from
the upper catchment of the basin to better meet the downstream water requirements for
irrigation, urban and industrial uses, follow a regular pattern with moderate
variability. But the limited year-to-year carryover storage in the reservoir makes the
basin vulnerable to prolonged periods of drought.
Water releases from the Chadegan reservoir also show a predictable pattern, with the
only deviations occurring during flood events. There is a high reliability of meeting the
water requirements during periods of peak demand. But releases during the winter
months, at the end of the irrigation season, are lower and more variable. This results in
low discharges in the Zayandeh Rud and reduced water quality, especially in the lower
reaches of the river.
A simple water-balance approach was used to estimate the proportion of return flows in
the basin. An average annual value of 30% was obtained, with the magnitude of return
flows being particularly important in the lower reaches of the basin. But more
investigation, especially including groundwater and water quality aspects, needs to be
carried out before a definitive value can be advanced.
Given the limited supply of fresh water in the Zayandeh Rud basin, further water
resources development and water management improvements can only be envisaged if
there is scope for real water savings in the basin. This can be assessed if a basin-wide
approach, leading to a good understanding of water use (and reuse) at the farm, system
and basin levels, is adopted.
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Introduction
The Zayandeh Rud is a vitally important river for agricultural development, domestic
water supply, and overall economic activity of the Esfahan Province in central Iran.
However, population growth and greater industrial activity have increased the demand
and competition for water resources in its basin. The agricultural sector has been
particularly affected. Water shortages not only make it difficult to irrigate the full extent
of irrigable land, but also lead to the salinization of soils in the lower portions of the
Zayandeh Rud basin and a reduction in the quality of return flows into the river. The
lower reaches of the river downstream of Esfahan are further polluted by ever-
increasing quantities of urban and industrial effluent being returned into the river.
The IAERI-EARC-IWMI Collaborative Research project, established in 1998,
addresses the question of how integrated approaches to irrigation and water
management can contribute to sustaining agricultural productivity in the Zayandeh Rud
basin, taking into account the multiple uses of water in the basin.
Water use, and especially the scope for further water resources development, cannot be
ascertained by analyzing water utilization only at the farm or system level. Proper
accounting of water availability and water use at the farm, system and basin levels is
required, particularly in the context of limited supplies of fresh water and multiple uses
of the available resource. Return flows from seepage, percolation and surface runoff
traditionally considered as “losses” at farm and system level must all be taken into
account. Molden (1997) proposed a water accounting framework where water balance
components are classified into water-use categories that reflect the consequences of
human interventions in the hydrological cycle.
It is also worth noting that a number of authors (Seckler 1996; Keller et al. 1996; Perry
1996; 1999) have raised questions regarding the traditional concept of irrigation
efficiency, which typically relates the volume of water beneficially used (i.e., crop
evaporation) to the amount of water diverted to a use. First, increases in efficiency at a
local level do not necessarily lead to water savings at a basin level. Second, increases in
efficiency defined in this manner are not necessarily better. For example, higher
evaporation with the same diversion may lead to environmental degradation, or water
may be evaporated by a less beneficial use. To get a better indication of how well water
is being used and of the scope for additional beneficial use, it is perhaps preferable to
compare the amount of water depleted by various uses deemed to be beneficial, to the
amount of water available for use in that basin -- the concept of basin efficiency
proposed by Molden and Sakthivadivel (1999).
This paper provides an overview of the hydrology of the Zayendeh Rud basin, from the
point of view of the inflows into Chadegan reservoir, the releases from the reservoir,
and the regulation and use of flows along the river for irrigation and other purposes. A
rough water balance of the basin highlights the challenges related to managing and
improving the productivity of water in a closed basin, especially in regard to the need to
correctly assess the degree of return flows when seeking water management
improvements.
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The Zayandeh Rud Basin
Physical Description
The Zayandeh Rud basin lies in central Iran (Figure 1). It is a completely closed basin
having no outlet to the sea. The river is about 350 km long and runs in a roughly west-
east direction, originating in the Zagros Mountains, west of the city of Esfahan, and
terminating in the Gavkhuni Swamp to the east of the city. The Zayandeh Rud provides
irrigation, domestic and industrial water to Esfahan Province, which is one of the most
important economic areas of Iran.
The area of the Zayandeh Rud basin is some 41,500 km2. However, only the area
upstream of the Chadegan reservoir makes any significant contribution to the
streamflow. Below the reservoir there are virtually no inflows into the river, and they
are so infrequent that it would be impossible to use them in any planned manner. The
total water supply in the basin is augmented by the diversion of water from the Kuhrang
River in Chaharmahal-va-Bakhtiari province into the upper reaches of the Zayandeh
Rud. Two diversion tunnels in operation since 1986 can deliver 540 million cubic
meters of water a year while a third tunnel, expected to be ready in a few years, will
deliver a further 250 million cubic meters of water annually.
Figure 1: Location of the Zayandeh Rud basin
Esfahan
Zayandeh Rud
Basin
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The Chadegan reservoir provides storage of winter and spring runoff and its releases are
used to regulate flows in the river. There is a series of diversion weirs along the river,
and numerous locations where urban areas and industry can extract water.
The upper catchment covers about 4,000 km2 or less than 10% of the total catchment.
The upper catchment is mountainous, with peaks rising to as much as 3,500 meters, and
there is little utilization of water upstream of the reservoir. There are natural forests in
the upper catchment although most of the higher land is barren.
The central and lower portions of the valley are natural arid and sub-arid areas. Steep
mountain ranges rise up out of the valley floor, but the majority of the landscape
consists of gently sloping alluvial fans with dry streambeds where there are occasional
flash floods in rare storms. The natural vegetation here is sparse thorn bush and drought
resistant grasses, and there is a high percentage of bare rock and soil.
The basin terminates in the Gavkhuni Swamp which is a natural salt pan. Much of the
area surrounding the swamp is sandy and there are extensive dune areas just east of the
swamp. Water entering the swamp area is extremely saline, with EC values as high as
30 dS m-1 during periods of low flow (Salemi et al., 2000).
Climatic Conditions
The major part of the basin receives less than 150 mm of precipitation during the year,
almost all of which falls in the cooler winter months associated with fronts moving
eastwards from eastern Europe. Only occasionally is there enough rainfall to generate
significant runoff from the alluvial fans.
Most runoff originates from the mountains surrounding the basin, particular in the
Zagros range, and most of this runoff is in the form of snowmelt rather than direct
runoff from precipitation. This is illustrated by data from Kuhrang meteorological
station (elevation 2285 m), located to the west of the Zayandeh Rud basin, presented in
Table 1. More than 89% of the precipitation occurs between November and March, with
an annual average of 70 days of precipitation. Of these 70 days about 55 experience
snowfall rather than rainfall, and with cold winter temperatures that may not rise above
freezing for weeks at a time, most precipitation remains in the form of ice and snow
until temperatures rise in April.
The effect of spring snowmelt is that peak discharges are experienced during the time of
year when agricultural demand for water is also rising. This has enabled irrigation to
become an important economic activity for some centuries, and was the basis for the
historical importance of Esfahan several hundred years ago.
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Table 1: Average climatic conditions, Kuhrang (elevation 2285 meters), 1987-1996
Irrigation Development
With annual potential evapotranspiration in the order of 1500 mm, it is almost
impossible to practice any reliable agriculture in the Zayendeh Rud basin without
irrigation. In fact, many of the areas currently utilized for irrigation, particularly those
upstream of and adjacent to Esfahan City, were developed several hundred years ago
using diversion weirs to feed earthern canals on either side of the river. In addition some
alluvial fans have been partially irrigated using “qanats” or horizontal wells dug to
reach groundwater at the base of hills, or more recently, through boreholes.
However, it has only been in the past few decades that irrigation has been developed in
the form of large-scale, integrated systems with proper devices for conveyance,
distribution and measurement of irrigation flows. The location of the main irrigation
systems and the diversion weirs serving them are shown in Figure 2, while the main
data on the irrigation systems are presented in Table 2.
Ave.
Ave. Ave. Monthly Wet Days with
Month Max. Min. Daily Total Days Snow
October 18.5 4.5 11.5 47.3 5.6 0.1
November 11.9 0.1 6.0 191.2 8.6 3.6
December 4.9 -6.5 -0.8 249.5 12.0 10.4
January 0.5 -11.5 -5.5 204.6 12.9 12.4
February 2.6 -8.9 -3.1 250.3 13.2 12.6
March 5.6 -4.3 0.6 344.3 15.8 13.0
April
12.1 1.7 6.9 147.6 11.5 2.0
May 19.8 7.3 13.5 52.2 7.3 0.1
June 26.3 10.7 18.5 0.9 1.0 0.0
July 29.9 14.2 22.1 1.0 1.0 0.0
August
29.8 13.8 21.8 1.2 0.7 0.0
September 25.7 9.5 17.6 1.8 0.9 0.0
Year 15.6 2.5 9.1 1492.0 70.5 54.2
Precipitation
Air Temperature (
oC)
-8-
Abshar
Left
Abshar
Right
Borkhar
Mahyar
Nekouabad
Left
Lenjanat
Nekouabad
Right
Rudasht
Right
Rudasht
Left
0 50 100km
1
2
3 4
56
7
1 Regulating dam
2 Pole Zamankhan
3 Pole Kaleh
4 Nekouabad
5 Musiyan
6 Pole Chom
7 Varzaneh
Main Structures
Figure 2: Main irrigation systems and regulating structures in the Zayendeh Rud
basin
The Nekouabad Right and Left Bank systems were completely redesigned and
reconstructed in the late-1960s and early-1970s. The main canals are regulated using
‘Neyrpic’ hydro-mechanical gates, while diversions to most secondary canals use
‘Neyrpic’ modules to deliver desired discharges. Some tertiary canals, particularly those
in the older parts of the system developed long ago, remain earth canals with simple
control devices, but all newer canals are concrete lined trapezoidal canals. The Abshar
systems east of Esfahan are of a similar age to the Nekouabad system.
In recent years three additional areas of irrigation have been added: the Mahyar system
that is south of the main valley, and is fed by a canal from a diversion on the Zayandeh
Rud upstream of Nekouabad, the Borkhar system north of Esfahan town, and the
extension to the Rudasht system in the eastern part of the basin. All three of these
systems have had extensive groundwater development but can now rely primarily on
canal water deliveries from the Zayandeh Rud.
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Table 2: Main features of irrigation systems in the Zayandeh Rud basin
Name of System
Date of
Construction
Designed
Command
Area (ha)
Design
Discharge
(m3/sec)
Length of
Main Canal
(km)
Length of
Secondary
Canals (km)
a) Old Systems
Nekouabad Right Bank
Nekouabad Left Bank
Abshar Right Bank
Abshar Left Bank
b) New Systems
Borkhar
Rudasht Left & Right
Mahyar
1970
1970
1970
1970
1997
In Progress (a)
In Progress
13,500
48,000
15,000
15,000
36,000
47,000
24,000
13
45
15
15
18
50
10
35.3
59.4
33.5
36.0
29.0
209.2
120.0
45.0
76.6
38.0
33.0
Not completed
Not completed
Not completed
Note: (a) Rudasht is an ancient system being replaced with a new system
All new systems have conjunctive use of surface water and groundwater
Inflows into Chadegan Reservoir
Inflows into Chadegan Reservoir show a consistent annual pattern (Figure 3).
Figure 3: Average monthly inflows into Chadegan reservoir
0
100
200
300
400
500
600
700
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Inflow (million cubic meters)
1988 1989 1990 1991 1992 1993 1994 1995
1996
1997
1998
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The main period of runoff is from March to July when there is more than 150 million
cubic meters of inflow into the reservoir in each month, peaking in April and May when
average inflows exceed 300 million cubic meters (over 115 m3/sec). In contrast, winter
discharges are very low even though this is the period of maximum precipitation in the
catchment and from August to February, inflows average less than 100 million cubic
meters. Total average inflow is approximately 1700 million cubic meters per year
(Table 3).
Table 3: Summary of monthly inflow data into Chadegan reservoir, 1988-1998
(in million cubic meters)
Month Average flow Standard
Deviation
Coefficient of
Variation
Maximum Minimum
October 47.9 16.6 0.35 89.4 26.2
November 65.9 31.8 0.48 120.0 33.7
December 80.2 55.6 0.69 235.9 38.0
January 67.3 24.4 0.36 106.5 37.0
February 75.2 26.5 0.35 119.1 37.3
March 155.8 82.0 0.53 310.4 52.4
April 325.6 95.1 0.29 466.8 183.2
May 353.2 107.3 0.30 572.8 224.9
June 235.6 62.3 0.27 368.3 140.6
July 158.6 58.6 0.37 285.0 79.2
August 91.2 43.3 0.47 198.2 39.1
September 54.6 27.3 0.50 127.1 29.1
Annual 1711.2 412.3 0.24 2504.9 1134.1
Variability of annual inflows is only moderate. Annual flows during the 11 years of
available records, range from 1134 to 2505 million cubic meters with a coefficient of
variation of 24%. Monthly flows show greater variability, with coefficients of variation
ranging from 26% to 69%. However, April, May and June, the three months with the
highest average inflows, show the lowest variability (coefficients of variation about
30%) so that there is a high probability of reliable inflow during this time of the year.
As would be expected, months with lower inflows show rather more variability but this
is less important for water management as overall inflows are comparatively low in
those months.
Although the length of data availability is comparatively short, it is possible to estimate
the return periods of inflows on both an annual and a monthly basis1. For annual flows
(Figure 4) it appears that a total inflow of about 3,600 million cubic meters has a return
period of about 50 years.
1 It must be noted that the inflow records presently available with the project team include the
contributions from the trans-basin diversions from the adjoining basin. A more detailed analysis of
inflows into the Chadegan reservoir will be the subject of a forthcoming paper.
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Figure 4: Empirical probability of annual inflow to Chadegan reservoir
From the empirical probability distributions for monthly inflows (Figure 5), it will be
seen that the 50-year flood for May is likely to be in the order of 900 million cubic
meters while for February it is only about 200 million cubic meters. Flood peaks are
normally experienced during the period of annual snowmelt between April and June.
The largest monthly inflow recorded during the period of available data was 573 million
cubic meters in May 1992. In addition, 11 of the 12 highest flood months, when inflows
have exceeded 400 million cubic meters have been either in April or May (Figure 3).
The fairly predictable inflow pattern experienced at Chadegan reservoir simplifies water
management in general. The demand for irrigation water starts in April, more or less
coinciding with the onset of the main snowmelt period, so that it is not necessary to
have a full reservoir before the start of the irrigation season. Furthermore, the low
storage levels by the end of the irrigation season makes it possible to store flood water
that may occur before the onset of the winter freeze.
1
10
100
100 1000 10000
Annual Inflow (million cubic meters)
Return Period (years)
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Figure 5: Empirical probabilities of monthly inflows into Chadegan reservoir,
1988-1998
Pro bab ility of m ont hly i nflo ws in to C had ega n re serv oir: Octo ber- Dec emb er
1
10
10 0
10 10 0 100 0
Inf low (mill ion cubi c me ters per mo nth)
Return Periond (years)
Oc tobe r
No ve m b er
De ce m b er
Probability of monthly inflows into Chadegan Reservoir, January-April
1
10
100
10 100 1000
Inflow (milli on cubic meters per month)
Return Period (years)
January
February
March
April
Pr obab ility of m ont hly inflo ws t o Ch ade gan rese rvo ir, M ay-S epte mbe r
1
10
10 0
10 10 0 100 0
Inf low (mil lion cubi c me ters per mo nth)
Return period (years)
Ma y
Ju ne
Ju ly
Au gus t
Se p tem b e r
-13-
Releases from Chadegan Reservoir
Figure 6 shows the general pattern of rainfall, inflow and outflow at the Chadegan
reservoir.
Figure 6: Average monthly precipitation, inflow and releases at Chadegan
reservoir
The time lag of about two months observed between the major rainfall periods and the
maximum inflow into the reservoir clearly indicates the important contribution of the
snowmelt that occurs from March onwards.
The releases made from Chadegan reservoir show a very predictable pattern (Figure 7).
In those periods when the reservoir storage is around 1,400 million cubic meters, then
monthly releases are much higher than under normal conditions. These releases are
typically made in April and May, possibly in June, and once in December as a
precaution to keep reservoir levels low prior to the next snow melt season.
The three most obvious cases of flood control releases are in 1988, 1992 and 1993 when
sharp peaks occurred in the release hydrograph and monthly releases exceed 250 million
cubic meters. In 1995 and 1996, reservoir storage was also high but monthly releases
only registered about 220 million cubic meters.
Analysis of the relationship between monthly storage and releases shows that there is a
broad band into which all data points fit (Figure 8). This type of pattern indicates that
there is no period when storage levels were very high but demand was very low. As
long as storage is above 1,100 million cubic meters, then releases will be at least 150
million cubic meters during the next month, while if storage is less than 800 million
cubic meters, releases will not exceed 125 million cubic meters. These relationships
demonstrate that there is little effective year-to-year storage in the reservoir and that
almost all runoff from the spring and early summer is used by the end of the summer. In
0
50
100
150
200
250
300
350
400
October
November
December
January
February
March
April
May
June
July
August
September
Average monthly precipitation (mm)
0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
400.0
Average monthly inflow and releases (mill. cu. meters)
Precipitation
Inflow
Releases
-14-
this respect the reservoir has an effective runoff-delay capacity of some three months. If
there were significant year-to-year storage then there would be a less clear-cut
relationship between storage and releases.
Figure 7: Chadegan reservoir: Time series of monthly storage and releases,
Oct 1987-Sept 1998
Figure 8: Relationship between storage and monthly releases: Chadegan reservoir
0
250
500
750
1000
1250
1500
1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1993 1994 1994 1995 1995 1996 1996 1997 1997 1998
Storage on 1st of month (mill.cu.meters)
0
100
200
300
400
500
600
Monthly Releases (mill.cu.meters)
Storage Releases
0
50
100
150
200
250
300
350
400
450
500
0 200 400 600 800 1000 1200 1400 1600
Storage at start of month (million cubic meters)
Monthly release (million cubic meters)
-15-
These data also indicate that the reservoir, and therefore the entire Zayandeh Rud basin,
is vulnerable to a period of two consecutive years of drought. To date, from available
records, this has not occurred. However, given that normal annual release patterns
(excluding releases for flood control) require about 1,500 million cubic meters, if two
successive years of inflows of 1,200 million cubic meters or less occurred, then the
reservoir would not be able to meet all of the demand in the second year of a drought.
If the months when releases for flood protection are eliminated from the data set, then it
is possible to define the “normal” release pattern to meet downstream demand for
irrigation, urban and domestic water. This “normal” release pattern is shown in Table 4,
where all the flood control issues in April, May and June have been eliminated.
Table 4: ‘Normal’ average monthly releases (excluding releases for flood control)
The effect of this operational policy is to provide very consistent releases during the
period of most demand. With variability of less than 10% per month, the water flows
into the Zayandeh Rud are very reliable and predictable, and deviations from the
“ normal” pattern are all upwards because of flood control releases.
The pattern of releases also shows that winter releases are low. There is a policy not to
operate irrigation systems until April, so that during the three coldest months farmers
must rely on tubewell water should they require irrigation in this period. This also
means that discharges in the Zayandeh Rud are very low throughout the winter, making
the river susceptible to pollution from non-agricultural sources.
The release pattern shows more variation towards the end of the irrigation season, from
October to December. In years where there is more storage in the reservoir, releases in
these months tend to be around 150 to 210 million cubic meters while in years when
storage is somewhat lower, then the releases are reduced to the 80 to 120 million cubic
meters level.
Month Average Std. Dev. Variance
Oct 143.7 40.9 28.5
Nov 122.3 43.9 35.9
Dec 103.8 57.4 55.3
Jan 31.4 15.9 50.8
Feb 19.1 4.0 21.0
Mar 44.3 25.1 56.6
Apr 130.5 23.5 18.0
May 206.6 17.7 8.6
Jun 217.6 12.5 5.7
Jul 203.5 18.1 8.9
Aug 201.5 19.8 9.8
Sep 179.0 16.0 8.9
Annual 1579.0 215.1 13.6
Average Monthly Releases (mill.cu.meters)
-16-
Water Use and Extractions in the Basin
The water released from the Chadegan reservoir flows along the Zayendeh Rud and is
extracted at a number of points along its length for irrigation, domestic and industrial
uses. The location of the major irrigation schemes and diversion structures has already
been shown in Figure 2. The pattern of the average monthly volumes measured along
the river is shown in Figure 9.
Figure 9: Average monthly volumes measured along the Zayendeh Rud
The flow pattern outside the low-flow months of January and February is practically
identical at all the observation points.
There are only limited extractions between the Chadegan reservoir and the Regulating
Dam just downstream, and the Regulating Dam and the Zamankhan measuring point,.
Downstream of Khaleh, however, water extraction begins in earnest. The extractions
along the reach from Khaleh to Nekouabad regulator plus the extractions for irrigation
at Nekouabad itself account for almost half of the flow released from Chadegan.
The same pattern is repeated between Nekouabad and Chom when more than half the
remaining flow is extracted from the river, either for urban and industrial use in Esfahan
or for irrigation in the Abshar irrigation systems.
Further extractions for irrigation below Chom reduce flows at Varzaneh to almost
nothing, apart from floodwater releases that may reach this point. In fact, average
monthly measured discharges have fallen below 1 m3/sec on numerous occasions.
Worse, the quality of water reaching Varzaneh is extremely poor with high salt content
and many non-agricultural pollutants.
A simple spreadsheet-based water balance type of model was used to analyze the river
flows and the extractions for irrigation, urban and industrial purposes with a view to
0
50
100
150
200
250
300
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Flow volumes (million cubic meters)
Reservoir
Regulation Dam
Zamankhan
Khaleh
Nekouabad
Chom
Varzaneh
-17-
getting a better understanding of water use, and in particular, to assess the degree of
water reuse in the basin.
A monthly time-step was adopted and the analysis was performed reach by reach. The
response time of the river was assumed to be less than one month, so that there is no
time lag in water flows between months. A reach is defined between two successive
flow measuring locations along the river. Water extractions are considered to occur only
in the reaches.
For each reach, a fixed extraction of 5 million cubic meters per month (or 1.9 m3/s) was
assumed for urban and industrial use. For the Nekouabad-Pole Chom reach, an
additional extraction of 12 million cubic meters per month (about 4.5 m3/s) for the city
of Esfahan was included, based on a population of 2 million and a per capita
requirement of 200 liters per day. Observed monthly values of precipitation were used
and an effective area that is considered to contribute to the river discharge was defined
for each reach.
As for irrigation, the biggest consumer of water, historical data was available in respect
of the extractions by the main irrigation schemes. A few items of data were missing but
these were filled by using the average values for the same months. In addition, a
substantial amount of water is extracted by small-scale irrigation schemes in the river
valley. Details of how the extractions by these small-scale irrigation schemes were
computed are found in Droogers et al. (2000).
The model was run for the 10-year period 1987-88 to 1996-97, with a monthly time-step
as mentioned above.
It was found that the amount of water withdrawn from the system (computed on the
basis of the actual water flows measured at the different measurement locations along
the river) is very much less than the water extracted to meet the needs of the various
agricultural and non-agricultural uses within the basin. This is illustrated in Figure 10
for each of the 10 years considered2. The annual extractions, both net and gross, show
little or no year to year variation (coefficient of variation = 0.09).
This phenomenon seems to point to the existence of substantial return flows3 associated
with the different uses of water within the basin. Otherwise, the basic water withdrawals
by themselves would not be able to meet all the demands for water in the basin. The
average annual return flow percentage is estimated to be 30%.
2 The term ‘net extractions’ is used to refer to the difference in measured water flow between a given
node and another node upstream of itself. The term ‘gross extractions’ refers to the extractions required to
meet the different demands in a given reach.
3 Return flow (%) = (Gross Extraction – Net Extraction)/Gross Extraction
-18-
Figure 10: Average annual extractions and estimated return flows in the Zayandeh
Rud basin, 1987-88 to 1996-97
Figure 11 shows the average annual extractions, and the amount of return flows in five
of the reaches of the Zayandeh Rud4. It will be observed that in the more downstream
reaches (where there is substantial irrigation), the return flow percentage is almost 50%.
Figure 11: Estimated return flows in the different reaches of the Zayandeh Rud
It must be emphasized that the above analysis is a very rough attempt at assessing the
magnitude of return flows from the various uses of water (irrigation, industrial,
4 see figure 2 for the complete names of the reaches
0
500
1000
1500
2000
2500
1987-88 1988-89 1989-90 1990-91 1991-92 1992-93 1993-94 1994-95 1995-96 1996-97
Annual extractions (million cubic meters)
0
5
10
15
20
25
30
35
40
Return Flows (%)
Net Extractions
Gross Extractions
Return flow
N.B. Mean value of return flows over 10-
year period = 30%
0
100
200
300
400
500
600
700
800
900
Reg->Zam Zam->Kal Kal ->Nek Nek->Cho Cho->Var
Reach
Average annual extractions (million cubic meters)
0
10
20
30
40
50
60
Net extractions per reach
Return flow percentage
-19-
domestic and urban) in the basin. A more thorough analysis, taking into account
groundwater as well will have to be carried out to get a better estimate. The mixing-cell
approach described by Gieske et al. (2000) to quantify both irrigation and groundwater
return flows seems to be particularly promising.
Conclusion
This overview of the hydrology and water use in the Zayandeh Rud basin has brought to
light a number of salient points:
• Annual inflows into Chadegan reservoir show a regular pattern with moderate
variability (coefficient of variation 0.24).
• Monthly flows show greater variability with coefficients of variation ranging
from 0.26 to 0.69. But the flows from April to June, the three months during
which average flow is highest, have coefficients of variation that are less than
0.30, which means that there is a fairly high probability of dependable flows
during this period.
• The reasonably predictable flows into Chadegan reservoir simplify reservoir
management to meet demands under normal conditions, with special releases
needed to ensure the safety of the dam during flood events.
• The Chadegan reservoir does not have any significant year-to-year carryover
storage. Almost all the inflow during spring and early summer is released prior
to the next flood season, making the reservoir (and the basin) susceptible to
prolonged precipitation deficits.
• The ‘closed’ nature of the Zayendeh Rud basin is illustrated by the fact that there
is normally little water reaching Varzaneh and the Gavkhuni swamp (except for
flood releases that may reach these locations) situated at the tail-end of the basin.
The limited supply of fresh water in the basin has serious implications for
further water utilization and water management improvements in the basin.
• A simple water-balance approach was used to demonstrate the scope for reuse
and return flows within the basin among its various uses. The magnitude of
return flows was estimated at 30% over the whole basin, within the limitations
of the approach adopted. This aspect merits further study, especially to include
groundwater and water quality aspects, notably salinity.
The above points highlight the need to take an integrated, basin-wide approach when
studying water management in the context of multiple uses and users of the available
supplies of fresh water. A good knowledge and understanding of water availability and
water use at the farm, system and basin levels are essential. Water use and the scope for
real water savings cannot be ascertained by analyzing water utilization only at the farm
or system level.
-20-
In light of the above discussion, there is a clear need to reconsider conventional ideas
about water savings in the Zayandeh Rud basin. Apparent savings of water at the field
level do not always lead to real savings, especially if return flows from irrigation are
being reused. If the fraction of water supply depleted by evaporation and flows to sinks
is already very high because of reuse, there is little scope for saving water in the river
basin. On the other hand, if it were possible to achieve real water savings in irrigation,
such savings could be used for expansion of irrigation, or to meet increased demands
from other sectors such as urban water supply, industry, or the environment.
Acknowledgements
Numerous agencies, notably the Ministry of Agriculture and the Ministry of Energy,
allowed us access to their databases and provided us with essential information for our
studies. Their cooperation and support is gratefully acknowledged. The authors wish to
particularly thank Mr Assadi of the Esfahan Regional Water Office of the Ministry of
Energy, and Mr Ameeri, Director, of the Agricultural Master Plan of Esfahan Province
and his personnel for their assistance.
Literature cited
Droogers, P., H.R. Salemi and A. Mamanpoush. 2000. Exploring basin scale salinity
problems using a simplified water accounting model: the example of Zayandeh Rud
Basin, Iran. IAERI-IWMI Research Report 5. (in press)
Gieske, A., M. Miranzadeh and A. Mamanpoush. 2000. Groundwater chemistry of the
Lenjanat district, Esfahan province. IEARI-EARC-IWMI Research Report 4. (in
press)
Keller, A., J. Keller and D.W. Seckler. 1996. Integrated water resources systems:
Theory and policy implications. IWMI Research Report 3. Colombo, Sri Lanka:
International Water Management Institute.
Molden, D.J. 1997. Accounting for water use and productivity, SWIM Paper 1.
Colombo, Sri Lanka: International Irrigation Management Institute.
Molden, D.J. and R. Sakthivadivel. 1999. Water accounting to assess use and
productivity of water. International Journal of Water Resources Development
[Special Double Issue: Research from the International Water Management Institute
(IWMI)]. 15 (1/2): 55-71.
Perry, C.J. 1996. The IIMI water balance framework: A model for project level analysis.
IWMI Research Report 5. Colombo, Sri Lanka: International Irrigation Management
Institute.
-21-
Perry, C. J. 1999. The IWMI water resources paradigm: Definitions and implications.
Agricultural Water Management, 40(1): 45-50.
Salemi H.R., A. Mamanpoush, M. Miranzadeh, M. Akbari, M. Torabi, N. Toomanian,
H. Murray-Rust, P. Droogers, H. Sally, A. Gieske. 2000. Water management for
sustainable irrigated agriculture in the Zayandeh Rud basin, Esfahan Province, Iran.
IAERI-EARC-IWMI Research Report 1. (in press)
Seckler, David. 1996. The new era of water resources management: From “ dry” to
“ wet” water savings. IWMI Research Report 1. Colombo, Sri Lanka: International
Irrigation Management Institute.
-22-
The following reports have been published in the IAERI-IWMI Research Report series.
1. Water Management for Sustainable Irrigated Agriculture in the Zayandeh
Rud Basin, Esfahan Province, Iran. (2000) H.R. Salemi, A. Mamanpoush, M.
Miranzadeh, M. Akbari, M. Torabi, N. Toomanian, H. Murray-Rust, P. Droogers, H.
Sally, A. Gieske.
2. Exploring field scale salinity using simulation modeling, example for Rudasht
area, Esfahan Province, Iran. (2000) P. Droogers, M. Akbari, M. Torabi, E.
Pazira.
3. An overview of the hydrology of the Zayandeh Rud Basin. (2000) H. Murray-
Rust, H. Sally, H.R. Salemi, A. Mamanpoush.
4. Groundwater chemistry of the Lenjanat District, Esfahan Province, Iran.
(2000) A. Gieske, M. Miranzadeh, A. Mamanpoush.
5. Exploring basin scale salinity problems using a simplified water accounting
model: the example of Zayandeh Rud Basin, Iran. (2000) P. Droogers, H.R.
Salemi, A. Mamanpoush.
6. Sustainable irrigation and water management in the Zayandeh Rud Basin.
Proceedings of Workshop in Esfahan, Iran, 19-21 November 2000. (2001)
Anonymous.
7. Assessment of irrigation performance using NOAA satellite imagery. (2001) P.
Droogers, P., W.G.M. Bastiaanssen, A. Gieske, N. Toomanian, M. Akbari.
8. Water supply and demand in four major irrigation systems in the Zayandeh
Rud Basin, Iran. (2001) H. Sally, H. Murray-Rust, A.R. Mamanpoush, M. Akbari.
9. Spatial analysis of groundwater trends: example for Zayandeh Rud Basin,
Iran. (2001) P. Droogers, M. Miranzadeh.
10. Irrigated area by NOAA-Landsat upscaling techniques: Zayandeh Rud Basin,
Iran. (2002) A. Gieske, N. Toomanian, M. Akbari.
11. Crop and land cover classification by LANDSAT 7 ETM (July 2000) for the
Zayandeh Rud basin. (2002). A.Gieske, A.R. Mamanpoush, M. Akbari, M.
Miranzadeh.
12. Field scale scenarios for water and salinity management by simulation
modeling. (2002) P. Droogers and M. Torabi.
13. Water Supply and Demand Forecasting for the Zayandeh Rud. (2002). H.R.
Salemi and H. Murray-Rust.
14. Water Resources Development and Water Utilization in the Zayandeh Rud
Basin, Iran. (2002). H. Murray-Rust, H.R. Salemi and P. Droogers.
15. Groundwater resources modeling of the Lenjanat aquifer system. (2002). A.
Gieske and M. Miranzadeh.
