Erosion Risk Analyses On The Vodno Mountain And Impact To The Surrounding Areas

Ivan Blinkov1, Ivan Mincev2, Bozin Trendafilov12 1 Faculty of forestry – , Dept. of Land and Water - , bul.”Alexandar Makedonski “bb. 1000 Skopje, Republic of Macedonia ,fax: +389 2 3164560 ; E-mail: [email protected]; 2 Mediterranean Agronomic Institute of Chania, Crete, Greece, MSc student, Department of Environmental Managementе-mail: [email protected]

Abstract: Erosion has been an on-going problem for millennia. Forecasted climate changes will cause increase of erosion intensity because of the increase of the temperatures contribute to forest die-back, wild fires and soil degradation but increase of intensive rainfall frequency will dramatically intensify the soil erosion. In this paper there are presented hypothetical scenarios for intensifying the erosion processes in case of change of land cover i.e. loss of forest cover. The research was carried out on the Vodno Mountain. In the past, the city of Skopje was permanently endangered by the torrents from Vodno. The erosion control works (plantations, hydraulic structures...) started in 1952 enabling protection of the city. So the main goal of this paper is to implement GIS (Geographic Information Systems) in the existing methodologies of Gavrilovic for assessing soil erosion parameters. There have been used several standardized datasets for development of the GIS model (Land cover map, Erosion map of R.Macedonia, geological map, DEM, climatic data). Erosion GIS model has been created assessing the current situation and the hypothetical situations where the land cover was radically changed because of erratic conditions. Also the impact of the environment and the urban areas were assessed. Key words: erosion, risk assessment, Vodno, GIS

Introduction

In the last years there has been a huge development in the spatial representation and analysis of the data. The GIS (Geographical Information Systems) is an integral part of the new developments and it represents a big leap towards better understanding of the spatial extent of the environmental problems. The GIS represents set of tools which can make the life easier to the user. GIS modeling presents an opportunity to automatise the process of production of output with standardized input and already set parameters. The future of the solving of the environmental problems is to perceive the problems globally and to produce spatial data which will be available to the broad scientific community. Risk is a concept that denotes a potential negative impact to an asset or some characteristic of value that may arise from some present process or future event. In everyday usage, risk is often used synonymously with the probability of a known loss. Usually, the probability of that event and some assessment of its expected harm must be combined into a believable scenario (an outcome), which combines the set of risk, regret and reward probabilities into an expected value for that outcome. Paradoxically, a probable loss can be uncertain and relative in an individual event while having a certainty in the aggregate of multiple events. Risk management is the human activity which integrates: risk recognition, risk assessment, developing strategies to manage it, mitigation of risk using managerial resources. The strategies include transferring the risk to another party, avoiding the risk, reducing the negative effect of the risk, and accepting some or all of the consequences of a particular risk. Erosion damages could be on -site: soil losses; water loss, landscape deterioration and off-site: torrential flash floods >> damages on houses and infrastructure, filling up reservoirs, mechanical and chemical pollution of the water. Regarding erosion risk analyses, it should be separate: based of on-site damages of erosion and off site damages of erosion. Beside it should be separate: actual erosion risk and potential erosion risk.

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 1/8 Risk maps based of on-site damages are necessary for sustainable planning in agriculture and forestry on the hilly and hilly mountain region. Beside it, this type of map is necessary for spatial planning and planning of different infrastructure that pass the study region. The downstream region is located in the valley and risk of on-site damages is neglected. In these regions should be created the other erosion risk map based on off-site damages. This map should be used for sustainable spatial planning, urban planning, planning of other infrastructure and economic activities inn the valley. Large number of other institutions can use these maps as: insurance companies, institutions related to protection and rescue etc. In recent time there have been several attempts to implement the already established scientific models into the GIS environment. There have been several developed software packages which implement these algorithms into the spatial-digital environment (WEPP, ARC-INFO, USLE, KINEROS…..). The main ideas of this study are: - To create erosion risk maps based on "on-site" damages. - To use the existing national datasets which are with standardized quality and to implement them in the existing developed methodologies, like the one of Gavrilovic.

Aims and objectives

The aim of this study is to create GIS-model for assessment erosion and torrential risk based on the methodologies of Gavrilovic. Erosion Risk was assessed as: a) Actual risk (based on present situation) b) Potential risk (was created scenario for hypothetic situation)

The objectives of this study are: a) To recognize erosion risk b) To create basic numerical and graphical (GIS) dataset c) To assess the on site erosion risk using GIS

Methodology

The issue of soil erosion and torrent control has very crucial spatial extent. GIS systems encompass all the important tools for this purpose. First activity was collecting of basic dataset: maps, tabular data etc. After all maps were scanned, digitized and georeferenced. Then field activities were carried out. Field activities consisted of: recognition of the terrain with comparison to the previously prepared maps, GPS surveying, photo interpretation, surveying of the elements of the hydraulic structures. After that data from terrain was transferred to PC and implemented into the basic GIS-model. Beside it, all previous basic paper versions of different maps from different sources was digitized (scanned, georeferenced, drown). For estimation of the needed parameters, part of the basic data was reclassified according to the methodology requirements. The mostly used methodologies related to erosion and torrents in the R. Macedonia are by Gavrilovic. In this case study two main methods have been tested for applied GIS use: - Estimation of erosion coefficient – Z - and transported sediment - G; (Erosion Potential Model by Gavrilovic) For estimation of the erosion coefficient Z was used the following formula Z = γ xa (ϕ+ Jsr0,5) γ - reciprocity value of the resistant coefficient to erosion (extracted from the soil/geology maps) xa - soil protection by natural or man made cover (extracted from land cover map where was added erosion control works) ϕ - coeff. of visible erosion processes (extracted from terrain carried out map) Jsr - mean inclination of the catchment (extracted from the DEM) Greater part of the parameters was automatically extracted from the digitized layers with statistical tools.

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Study area and development of dataset

Study area – basic information

A few centuries B.C., the Vodno Mountain had been covered with good forest. The valley of the at Skopje was populated by the Illyric tribe of Dardani whose capitol was Skupi (ancient Skopje). Not until the reign of Justinian was a new town erected on the site, a settlement which developed rapidly in the 9th and 10th centuries and became an important Byzantine centre. After that Skopje was a centre of the Serbian Kingdom (king Dusan – 14th century). Skopje was a great trade centre of the (XV-XX century).All former cities have been located on the left side of the river Vardar. There are a lot of reasons for this. A part of the area along the river on its right side has been permanent affected by Vardar floods. Torrential floods have affected the other part, located on the foot of the Vodno hillside. The bigger part of the right side was unsuitable for living. During the history, people who lived in Skopje (and previous settlements) cut forest from the mountain Vodno to fulfil all their needs for tree (fuel wood, constructive wood …). It was extremely on the north slopes of the mountain. As a result of over cutting, irregular agricultural activities and overgrazing, mountains Vodno became bareland. Results of these were increasing of erosion processes, torrential flows, loss of biodiversity etc. After the II world war, exactly after the biggest flash flood in the XXth century caused of torrents from Vodno, erosion control activities on the mountain Vodno started. The last “big one” happened in 1951, when there was 1 dead, a lot of injured, but material cost was considerable. On the part near the foot of the mountain, as a result of intensive erosion processes and transport power of the water from the Gornovodnjanski Poroj, there was about 25000 m3 sediment in the city. A lot of bareland was afforested. Almost all torrents on the north slopes were regulated with hydraulic structures. Few acts or sub act regulative were proclaimed. Educative measures contribute to present situation. Beside other, all above activities enabled migration of the greater part of the city on the right side of the river Vardar. Now, Vodno is “the lungs of Skopje”, the most important green part in the city of Skopje and its neighbourhood, so the Macedonian government proclaimed part of the mountain as a park-forest. Maintenance of the present forest cover (silvicultural activities, protection from: fires, pests, disease from illegal cut, from illegal construction and afforestation of the existing barelands) are necessary for the improvement of the quality of life and safety of the citizens of Skopje and the settlements from the southern side.

Figure 1 - Location of the study area

The dataset was comprised of: 1:25,000 topographic maps; Land cover/use map, vector (1:50,000); Geology map, vector (1:100,000); Soil map; Torrential map; Drainage map; DEM (Digital Elevation

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 3/8 Model), raster; Climatic data; tabular data etc. Basic data was prepared for the part of the i.e. for the territory of the park-forest. The dataset was comprised of the following layers: 1:25,000 topographic maps, CORINE land cover/use map scale, vector (1:100,000); Geology and soil map, vector (1:25,000); DEM (Digital Elevation Model), raster; Map of torrents; Data from terrain measuring with GPS; Climatic data, tabular data etc. Basic dataset

Figure 2. Part of the basic dataset for the park-forest Vodno – developed GIS layers

The study area was covered on four 1:25,000 topographic maps produces by the National Geodetic service. The maps were scanned on A0 scanner to avoid further distortion of the data. After, the maps were geo-referenced and registered according to the national geodetic system. The existing CORINE land cover/use was used for establishing the vegetation parameters. The CORINE land cover/use map was developed by the EEA with scale of 1:100,000. The land cover classes were extracted from Landsat ETM+ satellite imagery with the method of photo-interpretation. The DEM was with cell size of 80m. The accuracy of the DEM was checked using trigonometric points from the topographic maps which are claimed to have accuracy of 0.5m by the producer. There were 198 points taken for accuracy and it yielded quite good results, the RMSE (Root Mean Square Error) was 18.9m. This map was used for extraction of some topography parameters. Map of torrents was prepared by digitizing on the basic topography maps in scale 1:25000. On terrain were detected and recorded with GPS all erosion control works: hydraulic structures, technical ameliorative structures etc. The climatic data were taken from the National weather service, to be more exact rainfall (annual average rainfall) and temperature (annual average temperature) data was collected from a time series of 40 years (1961-2000). Based on it were developed climatic GIS maps. On the map were determined several torrents and estimation were carried out on the whole territory. In the following text will be presented the basic parameters of the whole mountain: Sandstone and marl clay are parent rock on the lowest zone (5%) ; sands and sandy clay around previous (30%) plumbago-

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 4/8 sericit schist on the top zone (10%); but parental rocks of the south hill-side are : marbles , phylito- micha–schist and cipolin (55%). Dominant soils in the valley are alluvial soils and some of them are converted by human activities into hortisoils, deposoils and the lowest part of the valley are covered by marshes. In the hilly mountain region cambisol (eutric, districs, and cromics) is the dominant soil type. There are regosols, rigosols, rendzinas and small parts of terra rosa. Several torrents exist on the northern part of the mountain Vodno towards the city of Skopje. These torrents are divided in several zones. All torrents in west zone and central zone were regulated with longitudinal and cross constructions. There are main drains, drainage channels, barrages, thresholds, cascades …. The main drains collect water from torrents in each zone and transport it to the recipient Vardar via drainage channel. The same system of channels (1 main drain and 1 drainage channel) was built in the west and central zone too. The above channels were opened in past. Now, they are covered in the urban zone with concrete slabs. Total length of these channels is more then 6 km. At about 30 barrages were built. All these barrages are masonry which contributes to native ambient into the park-forest. Unfortunately, as a result of luck of finance those types of channels hasn’t been built or finished in the east zone yet. Due to urbanization there aren’t conditions of building this type of torrent management in the east zone. These torrents permanently damage the urban area. From the other side of the Vodno Mountain within the working area, torrents go to Patiska Reka (right tributary of Vardar). No one of them is regulated with hydraulic structures.

Results and discussion

In the following part are presented the erosion risk maps presented according to the erosion coefficient - Z and according to the mean annual sediment production - G (m3/km2).

The first map can be used for sustainable spatial planning, planning in agriculture and planning in forestry.

Figure 3. Actual erosion risk map - Z - erosion coefficient

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This map shows the risk zones in the study area where erosion control works or suitable forest or agriculture activities are necessary. The coefficient - Z in these zones is from 0,5 up to 1,5. In these zones construction of some infrastructure as roads, pipelines, electric lines, hotels, motels etc, should be carry out conditionally because erosion could damage the objects permanently. The average erosion coefficient of the whole territory is Z = 0,37. It means that generally erosion intensity is low.

The “what-if” scenario mean what’s happened if forest would be extracted as a result of forest fire, mass die-back because of pests, diseases, drought etc.

Figure 4. Potential erosion risk map - Z - erosion coefficient

This map shows the potential erosion risk of the area based on the relief conditions and without some land cover categories as different type of forest, etc. In this case large area would be attacked by the high erosion processes. In these case Z = 0,78 or 2,1 times more risk.

The risk is not equal everywhere. It depends of the watersheds. In the following maps are presented sediment production by different torential catchments. It is very important to be showed which part of the city of Skopje or the settlements around the Vodno would be attacked.

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The map shows the areas which are affected from erosion risk i.e. sediment production. Part of these material, depend of the relief conditions of the catchments and other factors as: rain intensity, torrential bad slope etc., would be transported to the downstream sections of the catchments i.e. in the settled area where damages would be significant. It can be seen that catchments No.:5, 6, 7, 8, 10, 12,13,14 have large erosion risk. These catchments are very significant because they affect large urban areas and therefore they bring large risks to the settlements. The catchments No.: 15 and 16 are also significant because a large residential area is planned there. In the moment this area is not affected by large risk but having in mind the large construction work which are planned there this area should be taken into consideration. In these areas erosion control works should be carried out.

Conclusions

‹ Current erosion risk is low - Z=0.37 ‹ Potential erosion risk is high Z = 0.78 ‹ Few parts of the city of Skopje : Taftalidze, Kozle, Kapistec, Centar, Kisela Voda, Pripor, Usje where passed the torrents 7, 8, 10, 12,13,14 have large erosion risk and possible damages from the torrents that starrted from the Vodno Mountain. ‹ The catchments No.: 15 and 16 are also significant because a large residential area “Soncev grad - Sun city” is planned there and having in mind the large construction work which are planned there this area should be taken into consideration.

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 7/8 Recommendation

We are obliged to : - Protect the forest; - Clean up the existing channels; - Extract illegal bans Potential Erosion risk is high and we are obligated to protect the environment and citizens of Skopje and neigbouring settlements.

References

• Blinkov Ivan (2001). Erosion control, textbook for students of environmental management • Blinkov I., Mincev I., Trendafilov B., Jagev V., (2007), Basic GIS dataset necessary for different analyses in forestry, International conference 60 years Faculty of forestry Skopje, proceedings • Blinkov et all: Risk-Disaster management and prevention against natural hazards in mountaneous/forested region, INTERREG IIIb Cadses project, on-going project, report 2 • Mincev Ivan.,(2004) Use of GPS and GIS in forestry - diploma thesis • Trendafilov Aleksandar (2004). Erosion and torrent control , textbooks for students of forestry • Trendafilov Bozin (2007). Creation of basic dataset for the park-forest Vodno - diploma thesis

Acknowledgement:

This study is a part of the multinational project RIMADIMA - “Risk-, Disaster-Management & prevention of natural hazards in mountainous and/or forested regions” Ref.nr. 5D102 RIMADIMA, that is part-financed by the European Union through the programme INTERREG IIIb CADSES.

Project part-financed by the European Union

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