Journal of Environmental Science and Engineering B 1 (2012) 918-921
Formerly part of Journal of Environmental Science and Engineering, ISSN 1934-8932
Assessment of Soil Erosion in Mountain Watershed Ecosystems in Tirana-Region
Entela Çobani and Oltion Marko
Department of Environmental Engineering, Faculty of Civil Engineering, Polytechnic University of Tirana, Tirana 355, Albania Received: May 21, 2012 / Accepted: June 5, 2012 / Published: July 20, 2012.
Abstract: Land erosion is an increasing problem that is seriously affecting our country in recent years. In many areas of our country, mountainous and hilly territories suffer major erosion in both surface and depth, where the solids are deposited in the flat parts of the country, thus leading to a higher content of gravel in agricultural land and filling of the sewage networks. The phenomenon of erosion is greater in the vicinity of residential areas where damages are larger and more sensitive. One of the most vulnerable in our country in terms of soil erosion is the district of Tirana. This study had the main goal to define and categorise of erosion rates in natural environments of the forest economies of the Tirana,
自然肌理the rate of recovery of vegetation, slope and rainfall index, which will serve as information and guidance on the land use by farmers, communes and the state regulatory officials, depending on the ownership of these woodland surfaces.
Key words: Erosion, ecosystem, soil, slope, land cover, vegetation.
1. Introduction
Soil erosion represents one of the most destructive phenomena of the earth, by both surface and depth erosion. The relatively significant activity of water erosion that is observed in our country is favoured by many factors such as landscape, geological structure, slope, soil, climate, etc.. The increased intensity of erosion is closely linked with high rate of destruction of vegetation cover. The degradation of vegetation or its complete destruction is determined by many factors, especially by the socio-economic system of each country [1]. This is also observed in Tirana, where as a result of negative impacts caused by mankind on the natural environment, the erosion phenomenon is becoming more and more problematic, especially during periods of intense precipitation.
This phenomenon is also significantly affecting on massive slides which are already evident in many areas of the country, causing considerable damage to the
Corresponding author: Oltion Marko, Ph.D., research fields: soil erosion, forest, waste treatment technology, environment.E-mail:***********************.environment, and in the economy. A crucial role in preventing this phenomenon belongs to vegetation, especially the forest [2]. But the role of vegetation is not immediately seen after its installation.
2. Materials and Methods
Tirana area is one of the most typical areas of our country regarding the development of erosion.
The study and analyzing of the factors that influence the development of erosion is based on a methodology which is used to assess the risk of erosion also in other areas of our country, where data are collected according to the division of forest economies [2]. Regarding the separation of the vegetation coverage rate, it is done according to this grouping: up to 0.3;
0.4-0.7 and > 0.70 [3, 4].
Assessment of the risk of erosion as per the slope is grouped as follows:
0°-5°: little risk of erosion;
dcn6°-15°: moderated risk of erosion;
16°-30°: average risk of erosion;
31°-45°:
major risk of erosion;
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Assessment of Soil Erosion in Mountain Watershed Ecosystems in Tirana-Region
919
> 45°: strong risk of erosion.
Soil erosion rate is determined by comparing the open profile of land with the standard profile in terms of soil erosion at four levels as follows [5]:
Class 1: up to 25% of a horizon in most of the surface; Class 2: from 25%-75% of a horizon in most of the surface;
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Class 3: over 75% of the horizon and generally also a part of B horizon;
Class 4: deeply eroded soil, in such a way which presents a network streams with average depth or deep depth.
To express the degree of aggressiveness of the climate factor, the combination of the product of the amount of multi-annual mean precipitation with the sum of precipitation during the critical period, for each 100 m elevation above sea level is used, according to Eq. (1) [6]:
000
.10k v
r R R I ⋅= (1) I r —rainfall indicator;
R v —sum of multi-annual mean rainfall in mm; R k —sum of multi-annual mean rainfall during the critical period in mm;
10.000—coefficient of converting the results into reduced productive values.
From the literature indicator I r (indicator of rainfall) is classified as follows:
I r < 50: erosion risk of first category;
51 ≤ I r ≤ 80: erosion risk of second category; 81 ≤ I r ≤ 150: erosion risk of third category; 151 ≤ I r ≤ 275: erosion risk of fourth category; I r > 275: erosion risk of fifth category.
3. Results and Discussion一
小时的
故事 The total area of forest economies (the studied area) is 83.840 ha, divided according to the forest economies and the vegetation coverage rate which is as follows: As it can be seen from the data in Table 1, most of the forest area of Tirana district take part in the interval of 0.3 with 55%, then in the range of 0.4-0.7 with 27.5% and in the interval of 0.7 with 17.5%.
Table 1 Forest area according to coverage rate.
Area according to coverage rate (ha)
Up to 0.3 0.4-0.7 > 0.7 44,501.8 26,974.25 12,363.95
This shows that the forest vegetation in these economies is deteriorated, which directly affects the dynamics and development of soil erosion.
Field study of soil is made on the basis of expeditions carried on during the period of 2003-2006, and ongoing consultation with studies previously conducted in these economies.
For each main profile considered in the field, the relevant files were completed and for each horizon the morphological description was done where samples were taken from 500-1,000 g which were labelled and restudied in a subsequent stage.
From the analysis made in this area it resulted to have these land types and subtypes:
(1) Brown mountain lands which lie in the belt of oak forests ranging from 400 m to 1,400 m above sea level in height. This type of land is located in the form of two subtypes, according to the FAO classification Eutric Cambisols (CMe) and Rhochic Nitosol (NTr); (2) Fulvous forest lands which lie on land formations above the area mountain brown lands, at the height ranging of 1,200-1,800 m above the sea level. This type of land is found in the form of two subtypes, Humic Camisols (CMu Humic Nitosols (NTu));
(3) Brown meadows lands, or Haplic Phaeazems (CME).
The slope gradient is one of the main elements of landscape that has an impact on soil erosion. Given the fact that in this area the vegetation is degraded, the influence of inclination of the slopes will be greater. According to the management plans and inventories of forest economies and topographic maps, the categorization of slope was done as follows:
As seen from Table 2, the slope of the mountain in this area is from moderate to large. Soil erosion rate is determined by comparing the considered profile with the standard one, and in terms of soil erosion it is
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Assessment of Soil Erosion in Mountain Watershed Ecosystems in Tirana-Region 920
Table 2 The area according to the slope.
Area (ha) according to the slope
0°-5° 6°-15° 16°-30°
31°-45°
>
45° 4,104 4,117 66,761 8,364 494 classified in four classes:
Class 1 (E1): Up to 25% of the first horizon (A) in most of the surface;
Class 2 (E2): From 25%-75% of the first horizon (A) in most of the surface;
Class 3 (E3): Over 75% of the first horizon, and generally, part of the horizon (B);
Class 4 (E4): Deeply eroded soil.
In a more detailed way, the erosion rate is presented in Table 3.
As seen from Table 3, erosion in forested areas of Tirana district is quite large, where around 41% of the surface area takes part in the third and fourth grades of erosion.
Erosion by the vegetation coverage rate is made after determining the classes of coverage of forest vegetation, where by the surfaces with coverage rate (0.1-0.3, 0.4-0.7 and > 0.7), profiles were opened, in the same way as for determining the degree of erosion. In Table 4, it presents the distribution of erosion risk classes in function of the degree of coverage by vegetation.
As seen from Table 1, surfaces with coverage of 0.1-0.3 are the most affected by erosion, as a result of degradation of vegetation, while in areas with large scale of coverage (> 0.7) no erosion of class E4 is found. Table 5 presents the distribution of erosion risk classes according to the slope which characterize the area, where grouping according to the slope is done at five levels (0°-5°, 6°-15°, 16°-30°, 31°-45°, > 45°).
As seen from Table 5, the surface with small scale slope (0°-5°), no erosion of fourth class is found, while in areas of steep slope (>45°), only erosion of third and fourth classes is found. This shows the influence of slope in the development of soil erosion process. While erosion under rainfall index is done by calculating the average annual rainfall for 100 m above sea level, and the critical period is October-March. Results for this indicator are given in Table 6. Regarding the precipitation indicator, territories up to 100 m above sea level are classified in the first category, by 200-500 in the second category, by 600-1,100 in the third category, by 1,200-1,700 in the fourth category and for altitudes > 1,700 m above sea level in the fifth category.
Table 3 Rate of erosion.
Rate of erosion
E1 E2 E3 E4 ha % ha % ha % ha %
19,441 23 29,808 36 18,646 22 12,945 19 Table 4 Determination of the erosion rate according to the coverage rate.
Class
Area in (ha) divided according to coverage rate
Total (ha) 0.1-0.3 0.4-0.7
>
0.7
E1 2,745.60 7,467.6 9,228.25 19,441.45 E2 13,633.55 13,935.9 2,238.80 29,808.25 E3 18,703.80 2,044.95 896.90 21,645.65 E4 9,418.85 3,525.80 - 12,944.65
Table 5 Determination of the erosion rate according to the slope.中国行政区划改革 Class
Area in (ha) divided according to the slope
0°-5° 6°-15° 16°-30° 31°-45° >
兰越峰事件最新进展45°
E1 E2 E3 E4 3,115.3
824.4
164.9
1,438.1
2,058.9
494.1
126.5
14,181.8
25,159.4
18,411.1
9,009.1
706.2
1,765.5
2,471.7
3,420.8
-
-
103.8
389.2
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Assessment of Soil Erosion in Mountain Watershed Ecosystems in Tirana-Region 921 Table 6 Calculation of rainfall indicator.
Altitude above sea level (m) Rainfall
indicator I r
Erosion
risk category
100 86.4
I 200 99.3
II 300 113.0 II 400 127.5 II 500 143.0 II 600 159.3 III 700 176.8 III 800 195.0 III 900 214.1 III 1,000 234.0 III
1,100 254.8 III
1,200 276.4 IV 1,300 299.5 IV 1,400 322.5 IV 1,500 347.7 IV 1,600 373.0 IV 1,700 398.7 IV 1,800 426.2 V
1,900 454.1 V
2,000 483.0 V 4. Conclusion
From the study and analysis of search results, it will arrive at some preliminary conclusions of the study: The study area lies on three land types. Brown mountain lands lie in the belt of oak forests ranging from 400 m above sea level to 1,400 m. This type of land is located in the form of two subtypes. The study of vegetation shows that interventions with negative effects on the forest environment from anthropogenic factors seem to be quite large.
The current rate of erosion turns out to be quite critical. It is divided into four classes: first class includes 19,441.45 (ha) or 23% of the total area, the second class 29,808.25 (ha) or 36%, the third class 18,645.65 (ha) or 22% and the fourth class 12,944.65 (ha) or 19%.
According to the classification made by grouping classes of erosion according to vegetation cover rates, it shows that the surfaces of small scale coverage have more erosion of third and fourth class.
Based on the results of rainfall indices the erosion risk is distributed in five categories, from I to V.
In areas that are eroded and that present the risk of slippage or landslips it should be intervened by biological works, where these works should be made on those surfaces which have degraded vegetation.
In the upper parts of water catchment areas, where the amount of liquid and solid flow is less, protective fences with wood material must be constructed, as well as dikes with dry stone masonry with concrete.
In risk areas risk of slippage or landslips, hydro-technical works should be built with gabions, as they are more flexible.
In the main bed flow hydro-technical works must be constructed with cement mortar stone walls dimensioned according to given methods, taking into account the permeability of the terrain to be placed.
References
[1]O. Marko, Land Erosion and Measures of Restoration,
SHPLU Tirana, Tirana, 2010, pp. 10-35.
[2]O. Marko, Risk evaluation of masive forests erosion in
Vithkuqi area district of Korca, Ph.D. Thesis, Agriculture
University of Tirana, Tirana, 2006.
[3] D.B.C. Beasley, L.F. Huggins, E.J. Monke, ANSWERS:
A model for watershed planning, Transactions of ASAE
23 (1980) 938-944.
[4]Management of Land Cover in Watershed, FAO, Italy,
1977, pp. 55-80.
[5]O. Marko, Assessment of Soil Erosion Risk in Mountains
Watershed, DDS Tirana, Tirana, 2010, pp. 94-100.
[6]H.M.J. Arnoldus, An approximation of rainfall factor in
the universal soil loss equation, in: M. De Boodt, D.
Gabriels (Eds.), Assessment of Erosion, Record No.
198****4087,1980,pp.115-170.
.
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