by Kaveh Samiei

"A goal of landscape ecological urbanism might be to design and plan cities to increase, rather than to decrease, ecosystem services. This suggests exciting new areas of research in landscape and urban planning, from ways to measure landscape."
—Frederick Steiner, Landscape ecological urbanism: Origins and trajectories. (Steiner, 2011)

Cities should be an extension of our natural environment. But nature has rules by which it operates, and these must be built into urban designs that mesh the organic and inorganic parts of the city (Samiei, 2013).

During recent years, the municipality of Tehran began to work on rehabilitation of river valleys. Three projects now are completed or near completion. This great movement can improve and develop the quality and quantity of Tehran environment, which is in a dangerous and catastrophic condition — but only if planners, designers and other decision makers pay attention to all aspects of rehabilitation, especially ecological and environmental principles like connectivity, coherent hydrology, compatible plantation, controlled interfering, considering buffer zones and so on. The river valleys often are a neglected part of Tehran's urban landscape and most of them have tragic stories and inelegant features. Planning for their conservation and restoration should start for the remaining and unprotected rivers quickly because Tehran is the city of river valleys!

Tehran takes advantage of having this potential,but the approach and the circumstances and specific plans for carrying out rehabilitation projects are critical. Bringing the dream of a significant urban project into being needs the consideration all aspects of multipurpose and multilayered planning.

River valleys as ecological elements have always had key roles in creating mutual relations between man-made city spaces and nature. River valleys play important roles in the provision of fresh water resources, natural green and blue corridors for climate moderation, green open spaces, biodiversity, parks, recreational areas, as well as places for public services. Investigations of the current condition of Tehran's River valleys indicate that not only do they not increase the quality of environment, in fact they play a negative role (Bemanian, 2008).

Tehran, the capital and largest city in Iran, has experienced rapid growth, especially in the past three decades. Tehran has more than 12 million inhabitants and despite all the efforts by responsible organizations to improve environmental conditions, it is contaminated with various environmental pollutants and its ecological structure has experienced numerous degradations. Recent development of parks and public green space has not been able to restore an ecological network fragmented by unplanned and uncontrolled growth (Bahrami et al., 2012).

The ecological landscape of Tehran

Greater Tehran consists of three sections: mountainous, piedmont and desert. The mountainous section includes peaks over 1800 meters. In this section, due to the height and legal restrictions, there are no residences or construction. Thus Tehran has physically developed in the other two sections. The southern parts of the city have grown along a wide, flat desert. The city, however, cannot expand along the plain due to the high levels of Ground water and the arid zone. So the city can only expand in the western direction due to its suitable geographical condition and new residential estates have mostly developed in this direction. The topographical conditions of the city directly influence the spatial texture of the city, especially in the northern side (Tehran Atlas, 2014).

From the south toward the north, the altitude increases, from 900 meters in low areas to 1800 meters. This difference in height results in differences in weather, better vegetation and beautiful countryside in the north. As one moves from the south to the north, where are many changes in the natural environmental conditions, property value, access to services and social conditions.

Geomorphology of Tehran. Source: atlas.tehran.ir

The Alborz mountain chain in the north of the City, the river valleys of the Darabad, Golab Dare, Farahzad, Kan, Evin and the low hills and urban forest parks (e.g., Lavizan, Sorkhe hesar, chitgar, Quchak) are examples of primary landscape elements which are intrinsically linked with Tehran ecological network, and provide an essential sense of place which can be appreciated from many vantage points within the city. There are other more local landscape elements that can help give areas a sense of place and which can be referred to as secondary landscape elements (Bahrami and K.V.). Among other landscape features are natural and manmade patches, which give Tehran its unique characteristics and residential and touristic values. One of its most important natural patches are northern heights which endow the city with a special natural characteristic.

Today, Tehran has lost many of its natural patches due to rapid growth. Urban constructions have also caused the gradual destruction of natural patches, which were situated along geological corridors, near local water resources. The development of manmade natural patches has also shown that even though the number of parks and green patches has been increased, these newly natural patches have not been made sustainable. They have shown little efficiency due to their small size and lack of ecological integration. These patches have been made without paying attention to landscape capabilities and water and soil resources. As a result, most of the newly-established green patches have been built on uncultivated hills and lands without suitable water and soil resources. In Tehran, there has always been a shortage of water, and because of this, water has often been taken from other areas, thus causing the eventual destruction of more natural landscapes. Unfortunately, the newly-established green patches have not been able to perform as ecological substitutions (Barghjelveh and Sayad, 2011).

The natural-built matrix of Tehran's landscape varies from the natural mountains to the urban context. There are patches of nature in the center and an agricultural landscape and the desert edge in the south. The protected lands and forests in the east change to the very densely built areas in the center and also to open and built green areas in the west. Tehran's metropolitan matrix is defragmented by natural and built corridors, which provide the basis for a heterogeneous combination of natural and built patches that form the urban landscape structure and define its functions and transformations (Aminzadeh and Khansefid, 2009).

Therefore, with the increase of urban constructions and the continuous destruction of landscape's natural resources, there are no more valuable areas in Tehran that can be considered as natural patches. Except for large patches dispersed in the northern foothills and the margins of the city, which are ecologically disconnected, natural patches within the landscape are small ones. It is worth noting that patches near the natural corridors are ecologically historic as well as valuable in terms of extent. These areas are not only considered as landscape's micro-scale ecological patches, but due to their expanse and the presence of hydro-corridors, they are also able to act at the landscape's macro-scale ecological activities. These patches are also important in terms of having access to city's recreational potentials as well as different urban land uses and functions. These characteristics and capabilities add to the ecological importance of these patches.

Thus, the river valley corridors and remnant natural patches in the middle and built green patches in the east and west of the Tehran are considered as main structural elements in Tehran urban ecological system (Bahrami and K.V.).

Tehran's landscape network: natural & manmade corridors and patches. Source: Google Earth.

River valleys as natural corridors

Tochal peak is 3900 meters in altitude. Its main ridges overlook the southern slopes and Tehran plain, and forms small drainage basins. The rivers flowing in these basins are the life veins of the city. Water constantly flows in these basins and probably the main reason why Tehran developed is its hydromorphological conditions influenced by its northern heights. The most important basin, which covers the southern slopes of the northern heights of the city, include: Kan, Farahzad, Darakeh and Darband basins.

The seven north–south river valleys are characteristic of natural corridors of Tehran's landscape structure. They are fertile habitats that support a variety of flora and fauna and play significant roles as catchments and as places for energy and wind flows to remove air pollutions from the city environment, providing opportunity for connection with the natural upland–lowland context. Upland areas benefit from much better conditions than lowlands due to less environmental destruction caused by urban development. The natural hydrological corridors along the river valleys face more destructive factors and have less ecological functions from north to south because of their structural modifications. Natural corridors connect many natural and built patches scattered along them. These corridors are mostly oriented in a north–south direction. The east–west ecological connections are restricted due to the morphological structure of city (Aminzadeh and Khansefid, 2009).

The rivers and streams that run through these mountain valleys and inside the city are among the advantages of Tehran's landscape, and their ecological potential creates desirable urban patches within the manmade urban fabric. In addition to the provision of open spaces, concentration of main views and circulation of pure air, these natural corridors are among the major elements of Tehran's comprehensive plan to revive its landscape. In order to create continuous and expansive natural patches and assure spatial interconnection between natural greens and manmade spaces, these corridors are considered the main natural elements of Tehran's sustainability development plan.

Tehran's natural corridors, which run in main routes, do not have ecological buffers and as a result their ecological functions as connecting routes are limited. Even, constructed urban corridors (including riverside corridors and greenways) have urban functions due to being connected to urban zones. Thus, these corridors have special characteristics in terms of having important ecological and societal advantages in different landscape scales. The recreational potentials of these landscapes are also considerable. They are remarkable areas not only because they are rich ecological resources providing large green patches, but also because they are important cultural sites that provide the landscape's historic identity. Sometimes these areas along with their manmade urban elements benefit from the landscape's natural characteristics and become considered historic urban elements that define cultural functions. However, other times they remain poor in terms of plantation, and though they have the spatial capability to benefit from landscape's natural patches and corridors, nonetheless, they remain in need of good ecological connectivity. The vicinity of historic urban structures with valuable natural sites helps to protect the socio-ecological identity of the landscape. All these factors allow the manmade identity of the landscape to be in harmony with its natural and historic characteristics (Barghjelveh and Sayad, 2011).

A river valley corridor network may provide the needed spatial design closely adapted to ecological network layouts that also assure regional scale vertical connectivity within the upland-lowland context of the closed water basins continuum system of Tehran.

Tehran's landscape network: natural & manmade corridors and patches. Source: Google Earth.

Rehabilitated river valleys: Kan and Farahzad projects 

Recently, parts of Kan and Farahzad river valleys have been rehabilitated by the municipality of Tehran. Studying these two projects helps is understand the view point of those who have designed and planned them and finally gives a critical assessment of their method of river valley rehabilitation. Images from Kan river valley in 2008 and Farahzad river valley in 2004 shows the primary condition of two river valleys' site before starting site rehabilitation.

There are, at a minimum, two scales for analyzing urban river valleys projects: first, metropolitan scale and secondly, regional and local scale. In metropolitan scale, as landscape planning principles say, river valleys are important part of urban ecological network; they have potentials for connecting other forms of landscape ecology elements like urban patches. Therefore the river valleys of Tehran are the best options for doing the role of patch connectors in order to improving and restoring Tehran's ecological network.

By looking carefully at Tehran's ecological map and considering rehabilitation of Kan and Farahzad river valleys, it seems there has been no attempt at making connectivity to other patches or corridors! Also the density in some parts, particularly along two river valleys misses the chance for extending them into urban fabric in future. The other problem is many existing bridges of east- west highways, which usually cut the river valleys corridors and decline the ecological function.

Landscape planning should minimize isolation of natural landscape remnants and maximize linkages to provide for flows of energy, mineral nutrients, and species. An example of this would be to minimize barriers between the river valley and adjacent vegetation patches. (Baschak and Brown, 1995) It is apparent, as humans engage in landscape planning and design to restore previously altered ecosystems or protect existing fragments of natural systems, that the most effective way to restore or retain ecological integrity is to ensure that these elements are connected as part of a larger system. (Cook, 2000)

In local scale, the first comparisons between two images (after and before) rehabilitation show the obvious differences in land and river form related to direct interfering in natural features of river. In other hand, the urban river has been transformed to a big urban gutter! Even the inner sides and the bed of rivers are covered by concrete that have extremely impressed the hydrological function of river.

Rivers provide their regions with some natural benefits of critical importance and therefore that must be protected. Natural characteristics of river like meanders, backwaters, wetlands, and gradually sloped banks have important ecological functions. There are also benefits for inhabitant such as cleaner water and flood storage. It might not be possible to restore these features in many urban areas, but even a little effort can bring about a positive effect. Environmental improvements can be achieved on even the most heavily impacted rivers.

Farahzad river valley before (2004)(LEFT) and after (2014)(RIGHT) rehabilitation. Source: Google Earth

Kan river valley before (2008)(LEFT) and after (2014)(RIGHT) rehabilitation. Source: Google Earth.

Farahzad river valley after rehabilitation. Source: www.negahmedia.ir

Kan river valley after rehabilitation. The urban river has been transformed to a big urban gutter! Source: hamshahrionline.ir

Farahzad river valley under construction; imposing too many changes by interfering in land and river form will impress the ecological function of river valley! Source: www.eshiraz.ir

Protection of natural river features and functions necessitates avoiding the use of new dams and other engineering solutions, such as a straightening, channelizing, or placing streams in underground pipes and culverts. It might be possible to fully restore the ecological features and functions in most urban rivers and streams (Cengiz, 2013).

Imposing excessive hardscapes on natural and morphological forms of the site has eclipsed the ecological role of river valley in urban fabric. Although each construction project will impose itself on natural environment, it seems that the designers wanted to recreate the space and river's site in order to achieve other goals. Beyond the limit interfering in natural form of land and river and designing recreational park with maximum use of hardscapes without attention to ecological properties of site, prove that the rehabilitation have replaced by recreation! However both of the projects have different characteristics like site topography, river shape and so on, the designers haven't any other target except making a recreational space by the recreation of space!

In fact the ecological potentials of rehabilitating two of the limited natural elements of Tehran's landscape ecology has been failed and ignored completely!

Hardscapes are such places as roads, parking lots, sidewalks, driveways, paved paths, rooftops, and other impermeable surfaces that prevent rainwater from filtering through soil and replenishing rivers and stream as groundwater. Nearly half of all stream flows are provided by groundwater. This percentage can increase to a much higher level during drought periods (Alley et al., 1999). The urban rivers are also adversely affected by these impermeable surfaces of hardscapes as they do not absorb stormwater. In fact, they result in considerable increases in the volume and velocity of rainwater runoff. Another adverse effect of paved surfaces is their contribution to pollution as they washes surface oils, fertilizers, heavy metals, bacteria, and other contaminants into river and streams. Through the reduction of hardscapes and installation of natural landscapes, it can be possible to restore natural watershed functions, filter pollutant, and prevent erosion of banks and channelization of streambeds. The replacement of hardscape with soft, permeable surfaces, such as native grasses, shrubs, and trees in older, industrial or abandoned riverfront areas will improve environment from both aesthetic and ecological aspects. Planners must minimize the amount of hardscapes if they cannot be avoided. The reduction of hardscapes in new development projects can offer cost efficiency for local governments, developers, and homeowners. It is expensive to install and maintain infrastructure — roads, sidewalks, sewer liner, curbs and gutters, and parking spaces (Cengiz, 2013).

Another problem is the lack of attention to native and adaptable plantation. At first view during visits to both sites, the paucity of varieties and using ornamental and nonnative plants widely prove that claim! However, as old images show, the vegetation of two sites has been extremely poor. The poor and incompatible vegetation can't support and protect biodiversity and wildlife habitats across the river valley and so  it will lose its role of it as natural corridor. Unfortunately, most of the potential for creating rich green spaces has been missed due to paving for cycling, hiking, camping or parking lots.

Considering buffer zones for river valleys is another important principle that apparently has been neglected by designers and planners of the two projects. Buffer zones are areas situated next to a shoreline, wetland, or stream where development is restricted or prohibited. They facilitate the protection of ecological integrity of rivers, enhance connections between wildlife habitats, and allow rivers to function more naturally. A buffer network serves as "right-of-way" for a river or stream and it is an indispensable part of the stream ecosystem. Various sizes of buffers help protecting the natural areas close to rivers and streams, and especially fragile zone like steep slopes and wetlands. A well designed buffer zone helps protecting the quality of water and habitats for plant and wildlife. Buffers also provide shadow areas which decrease the temperature of water and thus protect aquatic habitat. With trees, shrubs, grasses and other native plants, they provide cover and food for birds, mammals, and other animals along the river. There are also benefits for humans as flourishing buffers are visually appealing and can often be used as greenbelts, parks and recreation areas. There is no advantage for biodiversity in keeping manicured lawns, formal landscape designs, and pruned shrubs as they frequently require the use harmful pesticides, and do not provide the food or shelter for wildlife (Cengiz, 2013).

Although the recreation feature of these rehabilitation have resulted in satisfied users, their lack to high quality ecological function will present major challenges in the future.

Other scientific researches (Barghjelveh and Sayad, 2011) also show that "in the process of regenerating the natural environment of Tehan's river valleys, including Farahzad River-valley, the principles of landscape ecology have been disregarded. In effect, no attention has been paid to the natural and ecologic potentials of these landscapes. In the case of Nahjolbalagheh Garden [Farahzad river valley], the project has been completed as if its only purpose has been to establish a beautiful garden. Disregards for the microclimate, the plant and animal diversity, the non-local plant cultivation incompatible with the context, unfavorable and nonsustainable cycle of matter and energy, infiltration of pollutants into the ecosystem (especially the ecosystem of river-valleys), and finally the absence of ecological connectivity to other urban landscapes are issues that may cause serious local problems and even the ecological destruction of Tehran's landscape in the not so distant future."

Existing bridges of east- west highways which usually cut the river valleys corridors and decline the ecological function. Source: Google Earth.

Left: The dominance of ornamental and recreational elements along with poor vegetation. Right: Construction within the boundary of river valley threats the buffer zone and river scenery! Source: tafrih.ir

Conclusion

Unfortunately, the study and evaluation of Kan and Farahzad river valleys rehabilitation projects demonstrates the necessity of changing minds and approaches when doing the similar projects in the future. The necessity comes from missing landscape ecological approach to design and planning in order to utilizing important potentials of Tehran's river valleys as natural corridors and connectors. River valleys are significant and inseparable parts of Tehran's landscape ecology and require more attention during the process of decision making by municipalities, planners and designers.

Based on the potentials and the restrictions of the landscape, the solutions for enhancing the ecological connectivity of urban natural public spaces are provided through the hierarchy of landscapes' Environmental Equilibrium, Geographical-anthropological Sustainability and Eco-environmental-societal Excellence features. By monitoring Tehran's river-valleys' content composition and spatial configuration variables, the functional quality of Tehran's natural resources is restored (Barghjelveh and Sayad, 2011).

The main focus is the application of the concept of eco-hydrology through the rehabilitation of the Tehran's river-valleys as an ecological network linking the landscape's highly attractive ecological, recreational and residential areas. The key element is the ecological management of the Tehran's river-valleys as the spatial link between geomorphology, vegetation, hydrology and land use, and as the integrated network between major natural corridors and patches within and outside the city, connecting natural and manmade green patches in order to improve the ecological networks citywide.

Kaveh Samiei
Tehran

On The Nature of Cities

References

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