RECLAMATION OF MEDITERRANEAN
URBAN BARREN LANDSCAPE.
THE CASE OF ATTICA GROVE.
Dr. ALEXANDER KANTARTZIS¹, Dr. GREGORY VARRAS²
¹Department of Floriculture and Landscape Architecture
Technological Educational Institute of Epirus
P.O. Box 110, 47100 Arta
GREECE
²Parks and Gardens Department
Municipality of Athens
Kanellopoulou 5, Athens
GREECE
Abstract: The once barren hills of Tourkovounia, today known as Attica Grove is one of Athens few forested urban landscapes. Ecosystem restoration, prevention of environmental degradation and urban sprawl has been achieved by top soiling and planting steep barren rock formations (outcrops), thus reclaiming environmentally sensitive open areas for public land use, resulting in landscapes possessing cultural and natural benefits to society.
Key-Words: Reclamation, Mediterranean Urban Barren Landscape, Landform, Top soil dressing, Replanting
1 Introduction
The area of study, known as the Attica Grove, covers the western highest part of the wider hill formation of Tourkovounia, and specifically refers to the part that is delineated within the municipality of Athens.
It is an area whose elevation spans between 220 to 231 meters above sea level. Its landform consists of washed limestone slopes with abrupt rock outcrops and more level surface on top of the hill, where today sites part of the G. Papandreou settlement.
In the past it had been a totally barren moonscape, but due to top soiling and replanting, one of Athens’s most prominent natural skylines has changed for ever.
2 Analysis of Study Area
2.1 Soils
The entire rock formation of Tourkovounia is made up of hard limestone with some patches of schist. The terra rosa soil, being a byproduct of the weathering of limestone, is confined to a limited number of shallow deposits [1].
Total absence of shrubs and trees along with sudden outpour of high storm water volume due to intense slope conditions, depleted the topsoil from higher elevations and deposited them to the lower residential area creating colouvial deposits on which the Department of Public Works had done some tree planting. This had left higher elevation barren areas and created a landform outline dominated by the grayish limestone of the Tourkovounia rock formation [2].
2.2 Slopes
Most of the barren study area (higher elevations) had a 30-60% slope, while the lower residential areas still to date has 0-30% slope.
2.3 Orientations-Solar Exposure
With respect to bioclimatic conditions -having a southeast to northwest solar orientation- the study area is characterized of the driest possible exposures.
2.4 Access-Landform
Access to the planting zones was made by special access roads that were created along with the forming of terraces [3].
2.5 Storm water runoff
Due to the absence of soil and vegetation, extreme runoff conditions burdened the lower areas with enormous amounts of excess storm water, causing headaches to the surface and underground storm water network. For example, on a storm of a 10cm rainfall, the entire study area of 200 stremmas (including the settlement) calculated with a runoff coefficient of 0.8, would produce a total volume of Q=200.000×0.10×0.8= 16.000m³ of storm water.
2.6 Vegetation
From a plant community standpoint, the region belongs to the thermomediterranean growth development (Oleo ceratonion) of the East Mediterranean. The bioclimate is intense thermomediterranean with number of dry days ranging from 125 to 150 (125<x<150). The bioclimatic floor is described as semidry with mild winter and minimum temperature during the coldest month between 3º and 7º C (3ºC< m<7ºC).
The main plant communities that had been degraded because of past human activities were: Ashodelus sp., Thymus sp., Genista sp., Phlonis fruticosa, Graminae and annuals. Density and composition of the existing vegetation was very poor throughout the year and not taken into account mainly due to very poor soil conditions. Young vegetation (~15 years old) that had been established artificially during the past and was considered to be reinforced included: Acacia cyanophyla, Robinia pseudacacia, Cupressus sempervirens, Cupressus arizonica var. glauca, Spartium junceum, Ceratonia siliqua, Cercis siliquastrum, Crataegus pyracantha, Eucalyptus sp., Pinus halepensis.
The above vegetation though in good health, was not fully grown due to limited irrigation, poor soil conditions and lack of fertilizing.
It can be said that there was no significant vegetation of importance prior to the top soiling and planting intervention.
Color, diversity, and broadleaves, features that characterize seasonal changes in the urban environment were all absent. The then existing vegetation was not integrated in leisure activities, transforming the potentially active user into a passive observant [4].
3. Synthesis
3.1 Soils-Landform
With efficiency, effectiveness and financial gains in mind, the entire area of study was divided into five sections based on inherent soil, landform and orientation characteristics as well as different intervention strategies for each zone [5]. There were no landform alterations made by means of digging or explosion. Most of the top soil came from the nearby Moustoxidi sub terrain garage excavation which was made up of alluvial deposits that had been washed out from the Tourkovounia higher grounds. Though dug soil depth ranged from grade ±0 up to -11meters, it had been mixed with soil from other similar projects within the Municipality of Athens, resulting in a soil type that had excellent mechanical and biological properties coupled with good fertility rates. As far as grain, soils were divided into three (3) categories:
a) Sandy loam fine-grained light soil. Digging depth is up to 6 meters.
b) Sandy loam with great amount of gravel. Digging depth is more than 6 meters.
c) In between category that had resulted from the mixture of the two aforementioned categories.
Exact placement of the above soil categories cannot be identified due to the enormous quantities imported in the site, but it is safe to say that the area ready to be planted was covered by alluvial soils of sandy loam to sandy clay texture. The pH fluctuated between 7,0 – 7,5.
So, the soil was returned to its original location, restoring decades of soil depletion and erosion.
At higher elevations, soil top dressing followed normal layering techniques. At slopes up to 60%, successive terraces of 5 meters width each, layered at an angle of 2:3 or 1:2, with a varied depth of 0,5-2,0 meters, were created for soil stabilization purposes.
The technique followed careful selection of deposit areas at higher elevations, from where the soil was then pushed down in order to form lower terraces. The later followed the existing landform contours by avoiding use of geometric shapes in order to fit within the natural environment and
integrate with local settings. This was achieved by means of bulldozers and other grading equipment.
Finally, four (4) types of surfaces were created:
a) Surfaces of low angle of inclination near and around the settlement, dressed with top soil.
b) Surfaces of slopes up to 60%, with successive terraces made up of imported soil.
c) Locations of limited soil deposits.
d) Barren land, where the natural steep rock formations did not allow for soil stabilization.
In general, the following four (4) landform design guidelines were established:
a) Terraces followed the existing natural contours. b) Use of geometric shapes was avoided, in order to comply with the natural character of the site.
c) Slope and terrace width could be varied according to local site conditions.
d) All final graded terraces would have a negative transverse slope of ~1% for storm water detention.
e) Compliance with all factors necessary for the site to receive new vegetation, such as removal or stabilization of large rocks, soil cultivation, soil stabilization with appropriate planting, and free storm water flow that would prevent soil erosion or landslide.
3.2 Vegetation-Replanting
Due to adverse local geological, soil and landform conditions it was very difficult - if not impossible - to engage in any planting activity. Planting methods and practices by use of explosives were abandoned due to the site’s proximity to the surrounding residential area. A required minimum planting soil depth of 1-1.5 meters was established. The accumulation and grading of the topsoil had to be done in away that would facilitate simultaneously both planting spaces and access roads for the graders. Maximum allowable existing slope for top soiling was set to 60%. Existing rock outcrops were to be left unharmed in order to be part of the scenic composition and be integrated into the natural character of the Attica region.
Species tolerant to limestone, heavy clay soils and indigenous colluvial deposits were:
Pinus halepensis, Pinus brutia, Cupressus sempervirens var. horizontalis, Cupressus sempervirens var. pyramidalis, Cupressus glauca, Cupressus macrocarpa, Laurus nobilis, Quercus coccifera, Olea oleaster, Olea europaea var. Chrysoplylla, Pistacea lendiscus, Pistacea terebinthus, Colutea arborescens, Celtis australia, Clematis chirrosa, Pyracantha coccinea, Lonicera japonica, Cercis siliquastrum, Rosmarinus officinalis, Pirus amygdaliformis, Amygdalus communis, Thuja orientallis, Thuja occidentalis, Evonymus japonicus, Asparagus acutifolius, Smilax aspera, Hedera helix, Ephedra campylopoda.
For rock covering and abrupt slopes:
Carpobrotus acinaciformis, Carpobrotus edulis, Lampranthus roseus
In imported soils the following species were used:
Robinia pseudoacacia, Acacia cyanophylla, Sophora japonica, Cassalpinia japonica, Cassalpinia sepiaria, Albizia julibrissin, Pittosporium sinensis, Melia azadarach, Gleditschia triacanthus, Nerium oleander, Spartium junceum.
At certain points lawn was created by mixing the following species:
Cynodon dactylon, Achillea millafolium, Festuca glauca, Dactylis glomerata.
3.3 Irrigation
For the first year and a half, there was no permanent irrigation system provided. Instead new plants were irrigated by conventional hand watering delivered by trucks. After that period an extensive underground and automated system was installed and operated for each terrace. Tap water was pumped from the base to the top of the hill, where a pump station was specially constructed and then distributed downhill for irrigation.
4 Conclusion
In reclaiming Mediterranean urban barren lands such as the Attica Grove, proper soil top dressing, landform and planting techniques were used in order to restore ecological balance, improve ecosystem habitat and integrate human leisure activities within the urban life and context of Athens, giving back to society landscapes possessing both cultural and natural benefits.
References:
[1] Craul, P., Urban soil in landscape design, John Wiley & Sons Inc., New York, 1992, pp. 396.
[2] Bullock, P. and Gregory, P., Soils in the urban environment, Blackwell Scientific Publications, Oxford, 1991, pp. 174.
[3] Harris, J., Birch, P., Palmer, J. Land Restoration and Reclamation: Principles and Practice, Addison Wesley, Longman Ltd., 1996.
[4] Sudbrock, A., Establishment of Woodland Groves for Urban Reforestation, Restoration and Reclamation Review, Vol. 1, No. 3, 1996, pp.168-172.
[5] Smith, M., Reclamation in Sudbury Ontario: the Greening of a Moonscape, Restoration and Reclamation Review, Vol. 1, No. 4, 1996, pp.95-112.