Zayandeh River (زاینده رود) is the largest river on the central plateau of Iran in Isfahan Province, flowing from west to east, and the most well known river of Iran after Karoon. It has come to be known by this name as a result of the many fields it irrigates on its course and thus brings them to life (for this reason it was formerly known as Zendehrood). Zayandeh River starts in the Zagros Mountains, from a natural pool known as Janan Spring, and travels 400 kilometers eastward before ending in the Gavkhouni swamp, a seasonal salt lake, southeast of Isfahan city. The Zayandeh has significant flow all year long, unlike many of Iran's rivers which are seasonal. The Zayandeh is spanned by many historical Safavid era bridges, and flows through many parks.
The Zayandeh River basin has an area of 41,500 square kilometers, ranging from an altitude of 3,974 meters to 1,466 meters. Its maximum length is 420 kilometers and its width ranges from 10 to 20 meters in the valleys to 800 meters in Isfahan. Zayandeh River water gives life to the people of central Iran mainly in Isfahan and Yazd provinces. Water diverted per person is 240 liters per day in urban areas and 150 liters per day in villages. The flow of the river has been estimated at 38 cubic meters per second. The Koohrang Tunnel aids in adjoining a part of the waters of the Karoon River to the Zayandeh River. Such tunnels enables Zayandeh River to provide water to the Yazd Province and with another tunnel in the works, Kerman Province will also be benefiting from Zayandeh River.
A hypothetical pre-historic culture is theorized to have flourished around the Zayandeh River in Iran in the 6th millennium BC. Archaeologists speculate that a possible early civilization existed along the banks of the Zayandeh River, developing at the same time as other ancient civilizations appeared alongside rivers in the region, such as the Sumerian civilization in Iraq and the Indus Valley civilization in ancient India. Archeological excavations in the Zayandeh River basin unearthed a 50,000 year old cave containing human and animal remains.
Zayandeh River crosses the city of Isfahan, a major cultural and economic center of Iran. In the 17th century, Shaikh Bahai, an influential scholar and adviser to Safavid dynasty, designed and built a system of canals to distribute Zayandeh River water to Isfahan's suburbs. Water from the Zayandeh River helped the growth of the population and the economy, helped established Isfahan as an influential center, and gave a green landscape to Isfahan, a city in the middle of a desert.
Until the 1960s in Isfahan Province the distribution of water followed a document claimed to date from the 16th Century. It divided the flow of the Zayandeh River into 33 parts which were then specifically allotted to the eight major districts within the region. At the district level the water flow was divided either on a time basis, or by the use of variable weirs, so that the proportion could be maintained regardless of the height of the flow. For centuries Isfahan had been an oasis settlement, noted for its surrounding fertile lands and prosperity. Until the 1960s industrial demand for water were minimal, which enabled the scarce water resources to be utilized entirely for agricultural production. With a growing population within the basin, creation of large steel works and other new industries and rising standards of living particularly within the city, the pressure on water resources steadily increased until the division of water was no longer feasible Approximately 80% of Zayandeh River’s water is consumed for agriculture, 10% for human consumption (drinking and domestic needs of a population of 4.5 million), 7% for industry (like the Zobahan’e Isfahan and Foolad Mobarekeh steel companies and Isfahan's petrochemical, refinery and power plants) and 3% for other uses.
The Chadegan Reservoir dam project in 1972 was a major hydroelectric project to help with stabilizing water flow and to provide generation of electricity. Since 1972, the Chadegan Reservoir has helped prevent seasonal flooding of the Zayandeh River. There have been a number of tunnel projects to redirect water from the Karoon River to the Zayandeh. These have helped provide water for the growing population and new industries in both Isfahan and Yazd provinces. In the section of the Zayandeh River crossing Isfahan, bridges, parks, paddle boats and traditional cafes and restaurants amongst the rest of Isfahan rich cultural heritage, are major tourist attractions for Iranian as well as international visitors. There are several new and old bridges over the Zayandeh River. Some of the bridges on Zayandeh River in Isfahan are as follows:
Shahrestan Bridge – Believed to have been built during the Sassanid era. One of the oldest bridges on Zayandeh River it bears much resemblance to Dezful and Shushtar Bridges, also from the Sassanid era.
Marnan Bridge - Built in 1599 and measures 160 meters long. It was formerly known as Sar Afraz Bridge, however, being a connection to Marnan Village it eventually adopted this name. It was built by a rich member of the Armenian community of the Safavid era.
33 Pol - Built in 1632 it is the longest, and one of the most famous bridges of Zayandeh River. It is also knows as Alahverdi Khan Bridge. Throughout history traditional Abrizan festivities took place at this bridge.
Khaju Bridge - Built in 1650, it is as well known as 33 Pol. It was frequently deorated and used for various celebrations.
Choobi (Joui) Bridge – Believed to have been built in the 17th century, it used to be an exclusively utilized bridge connecting Haft Dast Building to Sa’adat Abad Garden.
Felezi Bridge - Built in 1959 with a length of 136 meters. Constructed out of iron, it is located in the center of Isfahan and is frequently used by trucks and busses.
Bozorgmehr Bridge - Built in the 1970s and located in east Isfahan. It measures 130 meters long and 16 meters wide.
Vahid Bridge - Built in 1976 in west Isfahan, it stretches 130 meters long and 22 meters wide. It is heavily utilized by heavy duty vehicles travelling in the north-south direction.
Azar Bridge - Built in 1976. Similar to the Felezi Bridge, it is very solid but compared to the other bridges it lies very low with respect to the River’s average water level.
Ferdosi Bridge - Built in the 1980s, it runs north-south. Given that its neighboring bridges do not permit motor vehicle passage, it deals with a healthy dose of daily traffic.
As of late and as a result of climate changes, Zayandeh River has become seasonal. Unlike many of Iran's rivers it normally had significant flow all year long. However, as of 2009, the severe draught caused the river to completely dry up. It wasn’t until late in the year that water started flowing into the river again, bringing it back to life.
