The city of Isfahan is built around water in the centre of a vast desert plateau. The Zayandeh River, supplies water to the city from snow melt originating in the Zagros mountain range 200 kms to the west. Isfahan is famous for it’s bridges spanning the Zayandeh, most were built between the 12th and 18th Centuries. However the less publicised “rain gardens” of the old city are an equally impressive engineering achievement.
A pleasant dappled shade dominates the character of Isfahani streets. This is a striking and welcome contrast to the exposed expanse of surrounding desert. Environmental comfort on the Isfahani street far surpasses the hot and exposed streetscapes only a few hours flight away, in the cities on the southern side of the Gulf. The planners of Isfahan obviously had a clear vision of what makes a city street work in this harsh environment. These streets have some of the densest urban tree planting in the world.
Street trees and shrubs are planted in sunken gardens adjacent to the main carriageway. Today these open channels are called “rain gardens” or “infiltration beds”. These are part of the contemporary movement known as “green infrastructure” now sweeping the “developed” world. The rain gardens allow stormwater to infiltrate into the ground which can increase groundwater recharge and reduce peak flood flows.
Rain gardens address quality as well as quantity of stormwater runoff. The vegetation slows the rate of flow and so reduces sediment in the runoff. Rain gardens can further purify the stormwater runoff through phytoremediation, a process using plants and micro-organisms to filter and absorb pollutants.
The rain gardens of Isfahan are irrigated via flood irrigation (a traditional agricultural method). A system of manually operated valves are programmed to flood rain gardens on a regular schedule. The system is low tech and effective.
One common objection to flood irrigation is loss of water through evaporation. In this case the streets are well shaded. Evaporation that does occur helps to cool the street, and is working very well in the dry heat of the desert plateau. The impact on improving microclimate is tremendous. Streets without the rain gardens are punishingly hot in comparison. Streets with rain gardens are tangibly cooler (and more populated) than those without.
The rain gardens probably date from the time of laying out the streets in the 16 Century. This was the time of Sheikh Bahai (1547 – 1621), a scholar, philosopher, architect, mathematician, astronomer and poet of 16th-century Iran. “There is also no doubt about his mastery of topography. The best instance of this is the directing of the water of the Zayandeh River to different areas of Isfahan. He designed a canal called Zarrin Kamar in Isfahan which is one of Iran’s greatest canals.” Source: Sheikh Bahai Prominent Scholar of Safavid Era.
Coupling environmental function with aesthetic beauty is tied to the green infrastructure approach. Urban vegetation plays a key role. Today, urban policy makers and designers are improving quality of life in cities by understanding and applying this principle. This approach moves away from using urban vegetation as a mainly decorative or ornamental feature. Contemporary landscape architects, such as Dr Kongjian Yu support this move, as well as emerging engineers and environmental scientists. Dr Kongjian Yu’s article “The Art of Survival” captures the spirit of this new but ancient call to work with nature so to increase the ease of survival. Call it sustainability.
The rain gardens in Isfahan are bare earth yet free from rubbish or standing water. The city maintains them well. In some areas the bottom of the rain garden can be over 600mm below the adjacent footpath or road. All rain gardens drain to the main canals, and finally to the river.
Standards and codes in the developed world would not allow this difference in level and perhaps frustrate implementation of the entire system. The open channels could be seen as a safety hazard. Throughout the city small bridges allowed people to cross the channels safely. The people and stewards of Isfahan had accepted the potential “hazard” of open channels in exchange for a cooler, greener city, and a better quality urban life. Did the ancient Persians get it right?
Practitioners of Water Sensitive Urban Design (WSUD) today would be interested to visit the city of Isfahan. It is a shining example of using simple techniques to improve the quality of urban life through working with natural systems and urban vegetation.