assessment of erocivity of geological formations and transferred materials production of the...

7/27/2019 ASSESSMENT OF EROCIVITY OF GEOLOGICAL FORMATIONS AND TRANSFERRED MATERIALS PRODUCTION OF THE D

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CEST2009 Chania, Crete, Greece Ref no: 415/31-12-08

ASSESSMENT OF EROCIVITY OF GEOLOGICAL FORMATIONS ANDTRANSFERRED MATERIALS PRODUCTION OF THE DRAINAGE OF

THRIASSION PLAIN, GREECE

G. SIGALOS1, 2

, V. LOUKAIDI1

, S. DASAKLIS1

,A. ALEXOULI-LEIVADITI2 and A. MAVRAKIS3

1ArcEnviro Makrygianni 1 str, 157 72, Zografos, Athens, e-mail: [email protected] National Technical University of Athens (NTUA), Department of Minerals Engineering

Heroon Polytechniou 9 str., 157 80 Zografos, Athens, Greece3 Department of Economic & Regional Development, Panteion University,

136 Syngrou Av., GR-176 71 Athens, Greece

e-mail: [email protected]

EXTENDED ABSTRACT

The geomorphology and the lithology of an area is the basic factor that controls theerosional capability of the exogenic processes principally by the action of the water.The area of research is found at the Regional departments of Attica and Sterea Hellasand includes departments of prefectures of Western Attica and Viotia.The Thriassion basin occupies an area of 500 Km2 of which approximately 100 Km2

correspond to flat ground, while the rest corresponds to mountainous or hilly areas. Themorphology of the region is generally smooth, slightly dipping towards the sea, withmorphological slopes that do not exceed 3%.The broader area of the Thriassion Basin consists of geological formations of the Sub-Pelagonian geological unit, as well as of those of the geological unit of Eastern Greece,that is generally carbonate and /or dolomite formations of Upper Triasic to UpperCretaceous age that form the nearby mountains and mountainous areas, while the basinhas been filled by clastic sediments (marls, clays, conglomerates e.t.c.) since Pliocenetimes.In order to investigate the intensity and the erosion that can be seen in every area wefollowed the following methodology.We prepared a series of maps, which helped us to work out and analyze the factors thataffected the configuration of the relief. These maps are relative to the lithology of theformations, as well as their behaviour under the effect of the exogenic processes inconnection to his morphological slope, and can be divided into three groups:

A map providing information about the lithology and hydrogeology. In these maps, two

areas are distinguished according to the behaviour and resistivity to erosion.

Maps providing geomorphologic data due to the shape and the evolution of thedrainage networks of the area. In order to investigate the drainage texture, drainagedensity and drainage frequency maps were prepared. In each of these maps, threedifferent areas of density and frequency values were distinguished. A combination ofthese maps leads to a final map of the drainage texture in which two different areascan be distinguished.

A map of the slope of the valley sides. According to the gradient values of the slopes,

two areas were distinguished. One area with gradient of less than 12% and one ofmore than 12%.

The combination of the three final maps, of drainage texture, relief slopes and lithologicareas susceptible to erosion, produced the erosivity map. According to erosivity threedifferent categories of areas were distinguished. As the map shows the larger part of the

area belongs to the category of low erosivity.


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Finally in order to investigate erosivity under the present conditions we combined theerosivity map with the vegetation cover map. It is estimated that formations which arecovered by forest, are significantly protected, with lower erosivity than the uncultivatedareas.In this work we initially examined the degree of erosion vulnerability, as well as the

production of brought materials of the region that includes the basin of the ThriassionPlain.The regions characterised by high and medium vulnerability at extreme conditions (that iswithout considering the presence of vegetation), that are covered by dense forests shouldbe considered less vulnerable and be classified accordingly. On the contrary cultivationscan significantly increase the vulnerability of a region because they provide insufficientprotection toward erosive factors.The regions with high vulnerability at natural conditions (that is having considered thepresence of vegetation), are regions that have sharper morphological slopes, extensivehydrographical network, formations characterised by lower erosional resistance as wellas poor vegetation.

Key Words: Erocivity, erosive factors, drainage, transferred material production

1. INTRODUCTION

This paper examines the degree of vulnerability to erosion and transportation of sedimentload of the Thriassio basin, an extensive area that belongs to the Regional departmentsof Attica and Sterea Hellas. The largest section lies within the boundaries of AtticaPrefecture, while a small portion at the north enters the Viotia Prefecture. Near the Elefsiscoast lie the cities of Elefsis and Aspropyrgos.The Thriassion basin hosts the watersheds of Sarantapotamos, Agios Ioannis,Giannoulas and Remataki rivers, as well as the watersheds of smaller streams, especially

those near its margins (streams Souris, St. Catherine, St. Vlassis, etc.). The total area ofthe region is approximately 500 Km2, whose approximately 67% (335 Km2) is occupied bythe watershed of Sarantapotamos, the greatest river of the plain. The coastline of theElefsis bay has a length of approximately 19 km (Mavrakis et al., 2007).The topography of the area has been affected by intense neotectonic activity. The bay issurrounded by the mountains Pateras (West) Kitheronas (North), Parnitha(Northeast) and Egaleo (East). Their height, shape, boarders, orientation arecompletely controlled by neotectonic movements. It is also the presence of thesemountainous formations that gives the basin a variety of morphological environments,where steep slopes, especially near the mountains Kitheronas and Parnitha, give theirplace to flat areas, especially near the mouths of the larger streams of the basin.On a geological aspect, the broader of the Thriassion Basin area consists of geologicalformations of the Sub-Pelagonian geological unit, as well as of those of the geologicalunit of Eastern Greece, that is, as well as schist of Upper Paleozoic Lower Triasic age,generally carbonate and /or dolomite formations of Upper Triasic to Upper Cretaceousage, ophiolite rocks and flysch of Upper Cretaceous age that form the nearby mountainsand mountainous areas, while the basin has been filled by clastic sediments (marls,clays, conglomerates etc.) since Pliocene times.

2. DATA USED

The main factors controlling erosion are permeability and infiltration capacity of the

geological formations, drainage texture, slope degree and land cover. By combiningthese factors we are able to determine the vulnerability of these formations to erosion.


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For this work we relied on the methodology developed by Marinos et al, 1998 andsubsequently by Alexouli-Livaditi et al., 1999 and Sigalos & Alexouli-Livaditi, 2005, alongwith certain adjustments that seemed necessary.In order to carry out this work a primary database was created via digitising thecartographic background (topography, hydrographic network, geology) of the topographic

maps Athinai Elefsis and ErithraI of the H.M.G.S. at a scale of 1:50.000, as well asof the homonymous geological maps of I.G.M.E., also at a scale of 1:50.000. Dataconcerning land cover information were extracted from the Corine Land Cover project(CLC2000) carried out by the European Topic Centre on Land Use and SpatialInformation. Enriched by field investigations as well as literature, this primitive databasewould allow us to analyse the factors that control the shape of the relief and estimate therates of erosion.

3. PROCEDURE

The data analysis led to the construction of four thematic maps, presenting the main

factors that contribute to vulnerability of the formations to erosion, as follows.

Geological formations Resistivity Classification Map (A1): Permeability and infiltrationcapacity are the two main factors controlling the resistivity of the geological formations toerosion. Permeability controls the amount of annual surface runoff. Formations of highpermeability show low rates of surface runoff thus increased resistivity against erosion.Infiltration capacity applies primarily to soils. Continuous infiltration may cause soilsaturation, which is the primary cause for erosion. Formations displaying high infiltrationrates, such as carbonate rocks, allow water to run through their mass, without causingerosive effects. Similarly, formations of low infiltration rates, such as slates, do notcontribute to erosive effects. It is the formations of medium infiltration rates, such asneogene or alluvial deposits that usually lead to saturation and subsequently to erosion.

We thus divided the geological formations into three classes, based on their permeabilityand infiltration capacity rates. When combined, both permeability and infiltration capacityclasses resulted in the division of the formations into three more classes, according totheir degree of resistance to erosion. Table 1A displays the classification of the geologicalformations according to permeability, infiltration capacity and resistivity rates. Class A1corresponds to low resistivity formations class A2 to moderate resistivity formations andClass A3 to high resistivity formations.

Chart A1: Classification of resistivity rates.


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Drainage Texture Classification Map (A2): The second map (A2) displays the drainagetexture of the basin. This map was drawn after estimating the two most significanthydrological parameters: drainage density, defined as the total length of streams per unitarea and stream frequency. Both reflect relief ratio, geology, land cover as well as otherfactors contributing to soil erosion. A poorly developed drainage network decreases the

risk of erosion due to small rates of water runoff. On the contrary, the finest the texture ofthe hydrological network, the greater the risk of erosion is.As in the case of geological formations, three classes were distinguished for each of thehydrological parameters, that is low, moderate and high density, as well as low, moderateand high frequency. By combining the data, we resulted with three classes of hydrologicaltexture (low, moderate and high), as shown in Table 1B. According to this classification:class Y1 corresponds to small drainage texture, class Y2 to moderate drainage textureand class Y3 to high drainage texture.

Chart A2: Classification of drainage texture.

Slope Classification Map (A3): Water falling on steeply-sloped land runs off quickly andinfiltrates less than water falling on flattened areas, increasing the risk of erosion.The third map (A3) displays the surface of the Thriassion basin divided into areascharacterised by morphological slope gradients above 12% and slope gradients below12%. The slope gradient of 12% has been chosen as a classification criterion becausethis particular value is equivalent to the slope the talus cones present under diffusive flowconditions and thus considered as a critical angle of repose. Therefore, in areas withslopes greater than 12%, the corrosive process should be intense, while in areas withslopes gradients below 12%, this process is reduced. Table 1C displays the two classes

of relief slopes, based on the criterion of 12%.

Land Cover Protection Classification Map (A4): It is well known that the presence ofvegetation contributes to the soil protection against erosion. The thicker the vegetation,the greater the protection is. Thick forests and dense bushes provide great protection,while various crops protect insufficiently the formations against erosion. Areas bare ofvegetation are left almost unprotected (Valmis, 1990). Although narrow, urbanised areasare classified as poorly protected against erosive effects.Based on the types of the land cover information identified in the region, three classes ofland cover protection against erosive effects were distinguished: low (L1), moderate (L2)and high (L3), as shown in Table 1D.


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Chart A3: Classification of morphological slopes.

Chart A4: Classification of land cover protection

4. RESULTS

By combining the data displayed in maps A1, A2 A3 and A4, two erocivity scenarios canbe implemented: a first scenario at extreme conditions, corresponding to vulnerability ofsoils to erosion without taking into account land cover protection, as well as a second one

at actual conditions, corresponding to vulnerability of soils to erosion after havingconsidered the contribution of several land cover types to soil protection. Furthermore,two vulnerability maps were created for each of these scenarios.

Vulnerability to Erosion Map (Extreme conditions scenario): The importance of lithologyand hydrolithology, drainage maturity, relief and vegetation is expected to emergethroughout this paperwork. Each of these factors controls the erosion process for theThriassion plain. Their combination leads to estimations concerning the erocivity for eachpart of the plain. In an extreme conditions scenario, only data related to geology,drainage texture and relief gradient are taken into consideration. In general, areas withsteep slopes, fine drainage texture and low resistance to erosive factors are expected tobe more vulnerable to erosion, while flattened areas of coarse drainage texture and highresistance to erosive factors are expected to be less vulnerable.


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Table 2A displays classes of vulnerability created via a combination of formationsresistivity to erosion (A), hydrographic texture (Y) and slope degree (S) classes, asshown in Table 1. Class T1 corresponds to low vulnerability, class T2 to moderatevulnerability and class T3 to high vulnerability to erosion.

Table 1: Classification of the A1, A2, A3 and A4 chart parametersA Permeability

PermeabilityClassification

InfiltrationCapacity

Infiltration Cap.Classification

ResistivityClassification

Pervious 3 High 3 A1

Semi-Pervious 2 High 3 A1

Impervious 1 High 3 A2

Pervious 3 Moderate 2 A2

Semi-Pervious 2 Moderate 2 A2

Impervious 1 Moderate 2 A2

Pervious 3 Low 1 A2

Semi-Pervious 2 Low 1 A3

Impervious 1 Low 1 A3

B Drainage DensityDrainage Density

ClassificationStream

FrequencyStream Frequency

Classification

DrainageTexture

Classification

High 3 High 3 Y3

Moderate 2 High 3 Y3

Low 1 High 3 Y2

High 3 Moderate 2 Y2

Moderate 2 Moderate 2 Y2

Low 1 Moderate 2 Y2

High 3 Low 1 Y2

Moderate 2 Low 1 Y1

Low 1 Low 1 Y1

C Morphological Slopes

Slope gradient below 12%

Slope gradient above 12%

D Land Cover Type Protection Classification

heterogeneous agricultural areas, arable land, human activityareas

Low L1

various cultivations Moderate L2

forestry, scrub land, natural grassland etc High L3

Vulnerability to Erosion Map (Realistic conditions scenario): It is important to underlinethat land cover information, such as vegetation types (forestry, crop regions), urbanisedareas etc hasnt been included to our estimations while implementing the extremeconditions scenario for the vulnerability of the region. Indeed, land cover protectionagainst erosion is unquestionable and should be seriously taken into account, especiallywhen estimating hazardous risks, such as floods or the consequences of intense humanactivities, such as deforestation, large forest incinerations etc. Increased vegetationreduces surface runoff rates and increases the amounts of water that enrich the aquifersbeneath the earths surface.The combination of the B1 vulnerability at extreme conditions map to the A4 land covermap, gives us the vulnerability map B2 in actual conditions for the region. Table 2Bdisplays the vulnerability of the region, divided into three classes: low (TR1), moderate

(TR2) and high (TR3).


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Chart B1: Classification of vulnerability to erosion (Extreme conditions scenario)

Chart B2: Classification of vulnerability to erosion (Realistic conditions scenario)

Table 2: Classification of Erocivity under extreme and realistic conditions

A Erocivity (T) Low (1)Moderate

(2)High (3)

Combinations

A1-Y1-S1, A2-Y1-S1

A3-Y2-S1 A3-Y3-S1

A3-Y1-S1, A1-Y2-S1

A2-Y3-S1 A3-Y2-S2

A2-Y2-S1, A1-Y3-S1 A3-Y1-S2 A2-Y3-S2

A1-Y1-S2, A2-Y1-S2

A2-Y2-S2 A3-Y3-S2

A1-Y2-S2 A1-Y3-S2

BErocivity

(TR)Low (R1) Moderate (R2) High (R3)

Combinations

1-L1 2-L2 T3-L3

2-L1 3-L2 T1-L3

1-L2 T2-L3 T3-L1

5. CONCLUSIONS


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There are no major differences in the results between the two scenarios, as in both casesareas demonstrating low vulnerability are the vast majority.It should be noted that areas corresponding to high or moderate vulnerability classes, asshown in map B1, are covered by dense vegetation, should be considered as lessvulnerable and be classified accordingly. On the other hand, extensive crop areas provide

insufficient protection against erosive factors (Valmis S., 1990), which may increase theerocivity of these areas. This is related to their geographical distribution in the region.Indeed, crop fields cover flattened areas, without differentiating much the degree ofvulnerability, while forestry occupies areas of steep slopes, contributing to the reductionof the degree of vulnerability in the research region.Areas with high vulnerability: These areas have steep slopes, high drainage texture,present low resistivity against erosion and sparse vegetation. These regions occupy 2%of the total area in the extreme conditions scenario. When it comes to the realisticconditions scenario, due to the presence of vegetation, this proportion is reduced to 1%,because the area becomes less vulnerable.Areas with moderate vulnerability: These areas occupy 10% of the total area in theextreme conditions scenario, while in realistic conditions this proportion is reduced to 9%.

The small difference of 1% corresponds to areas initially classified as highly vulnerable(1%) and moderately vulnerable (2%), but subsequently demoted, as the presence ofvegetation hadnt been considered yet.Areas with low vulnerability: These areas have gentle slopes and small to mediumdrainage texture and vegetation. They occupy 88% of the total area in the extremeconditions scenario, while reaching 90% in the realistic conditions one. Although present,vegetation does not modify the vulnerability conditions considerably.

VULNERABILITY (T) AGAINST EROSIONExtreme conditions scenario

88%

10% 2%

Low Moderate High

VULNERABILITY (TR) AGAINST EROSIONRealistic conditions scenario

90%

9% 1%

Low Moderate High

REFERENCES

1. Alexouli-Livaditi A. and Livaditis G. (1997). Investigation and delineation of the areas where

intense erosion and mass wasting may occur at Tinos Island, Greece. Engineering Geologyand the Environment, 25-28, Balkema, Rotterdam.

2. Alexouli-Livaditi A. and Livaditis G. Lykoudi E. (2002). Investigation and delineation of areas ofintense erosion and product of waste materials at Lesvos island. Proceedings of the 6th Pan-Hellenic Geographical Congress, Thessaloniki (in Greek).

3. Mavrakis A., Dasaklis S., Christides A., (2007). Study of the characteristics of the ThriassionPlain streams and their contribution to the degradation of the marine environment of the ElefsisGulf. Proceedings of the 10th International Conference on Environmental Science andTechnology (10th ICEST), Vol. B, 461 468.

4. Sigalos G. and Alexouli-Livaditi A. (2005). Investigation and delineation of areas of intenseerosion and product of waste materials in the watershed of Sperchios river. Proceedings of the1st Scientific Session of the Geomorphology and Environment Commission of the HellenicGeological Society(in Greek)

5. Valmis S. (1990). Erosion conservation of soils. Agricultural University of Athens.6. I.G.M.E.: Geological Maps 1: 50.000. Sheets: Athinai Elefsis. Erithrai.


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7. H.M.G.S.: Topographic Maps 1: 50.000. Sheets: Athinai Elefsis. Erithrai.8. European Topic Centre on Land Use and Spatial Information. Corine Land Cover 2000.

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