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Procedia - Social and Behavioral Sciences 120 (2014) 749 - 756
The 3rd International Geography Symposium - GEOMED2013
The influence of lithology and soil on the occurrence and expansion of gully erosion, Toroud basin - Iran
Fatemeh Mousazadeh*, Khairnlmaini Osman Salleh
University of Malaya, 50603 Kuala Lumpur, Malaysia
Abstract
Gully erosion, is often associated as one of the most severe forms of soil erosion processes. Gully erosion forms after removal of soil along drainage lines from water surface after raining or thawing snow. Also gully erosion often results in much displacement of the soil mass, culminating in sedimentation, and degradation of the land. And has tremendous impacts on human activities which includes decreasing soil nutrients and agriculture productivity, river channel sedimentation and increasing floods and impact on water resources development within a river basin. Therefore type of the soil has a big role in its erosion and moving. According to the importance of the subject the research tries to evaluate the effect of soil and lithology on the formation and expansion of gully erosion and discover the erosion-sensitive area in Toroud basin- Iran. In order to achieve predetermined goals, the research examines two major objectives, which focuses on the effect of lithology and soil type on the formation and extension of gully erosion. To examine these objectives, this research uses GPS and GIS for preparing the maps. And also applies Soil test to define of the soil kind in this area. Hence Study in geology and soil type is a big conception for managing and using the land properly.
©2013TheAuthors.PublishedbyElsevierLtd.
Selectionandpeer-reviewunderresponsibilityoftheOrganizingCommitteeofGEOMED2013.
Keywords: Gully erosion; lithology; soil type; formation; extension.
1. Introduction
There are many researchers in the world that are interested to study about gully erosion formation and expansion. And the influence of lithology and soil are highlighted in many researches. As Gomez et al. said gullying is
* Corresponding author. Tel.: 0060-12-9711057 office: 0060-3-79675696 E-mail address: f_mousazadeh52@yahoo.com
1877-0428 © 2013 The Authors. Published by Elsevier Ltd.
Selection and peer-review under responsibility of the Organizing Committee of GEOMED2013. doi: 10.1016/j.sbspro.2014.02.158
considered as a complex process controlled by a diversity of closely connected factors: lithology, soils, climate, topography, land use and vegetation cover. Also the study in Colorado-US shows that commonly, gullies extend below the older prehistoric terraces linked with cultural sites to younger prehistoric and historic sandy flood deposits (Joel et al., 2003).
Expanding geomorphological examination during in Yellow river- China concluded and reported that the major loess gully systems have been outlining since the late Quaternary (Liu, 1965; Zhang, 1993). As it reported sheet erosion occurred at the shift from loess formation to Paleosol formation (Tang, Zhang & Wang, 1991). Also some researchers emphasized the importance of the soil and geologic materials exposed by the removal of vegetation cover and the impact of heavy rainfall on such materials (Okagbue & Uma 1987).
The research on lithology in Tunisia was presented by the Clay and Marl outcrops of the study unit relatively encrusted massive surface showing large and dense cracks during desiccation. It was believed that after rainfall soil infiltration will then decrease drastically and the high runoff rate increases the opportunity for gully erosion.
However, the bioclastic limestone outcrop of the study unit comprises the main chalky lumachellic crests at the northern part of the division. Furthermore, a dense gullying affected the Gypsum Clays of the unit and piping is very active in this formation. (Mennoubi et al., 2007)
In this research at Toroud basin in Iran investigation on the lithology and soil structure are very significant in the occurring and expanding gully erosion.
2. Material and Method
Toroud basin is located at 35°47'45" north latitude and 52°53'35" east longitude in Firouzkouh northeast of Tehran and in Semnan state, Iran. The surface area is approximately 874.5 hectares. And according to the gully map prepared by GPS in 2008, the surface of gully erosion in this basin is about 97.25 hectares.
Regarding to above mentioned objectives, this research tries to evaluate the effect of soil type and lithology on the formation and expansion of gully erosion. Hence to obtain this significant information need to visit the case study and make the interview in Toroud and watershed management of Firouzkouh and Tehran. And provide the map of gully erosion in this region after applying GPS in the line of gully land in the area and then coordinate them to get the gully map. Also digitize geology map by using GIS to find all kinds of lithology in this basin and then overlap with the gully map. As well as taking the profile of soil in 12 points in the head, mid, end and a point as a testifier for each gully. In every point soil sample took from different layers that totally are 35 samples and every layer approximately 1-2 kg of soil. The point of testifier has chosen with the distance of 20 meters from the main gully erosion line with the same shape, slope and land use but without gully formation. It is to determine the difference of soil type in the gully land with the land no gully happened in it.
3. Results
The result of this research shows that type of soil and lithology performs a great role in the occurrence and extent of gully erosion. The above mentioned studies approve the influence of soil and lithology to the occurrence and extent of gully erosion, and they confirm the influence of some sediments of Quaternary period, Aeolian dust, Paleosol formation, Clay, Marl, Bioclastic Limestone, Chalky Lumachellic and Gypsum on gully erosion. In Toroud basin the most sediment are related to the period of Eocene, Neogene and Holocene include Marl, Limestone, Shale, Salt, Tuff, Conglomerate, Sandstone, Alluvial fan and etc.
4. Discussion
Physical investigations on stone units are very important in the occurrence of gully erosion and its expansion. It can show the sensitivity of the land to erosion. In Toroud basin most of the sediment is related to the period of Eocene, Miocene and Holocene that include Marl, limestone, Shale, conglomerate, Alluvial fan deposits, sandstone and etc.
The most sediment in Toroud basin are related to the age of Eocene (shows by Em) that is included Marl, Marl stone, Limestone and Tuff with the surface of 2460.95 hectares in the basin and gully extent in 40.50 hectares (41.65 percent) of this sediment. The second sediments are related to the age of the Miocene (shows by M2) include Sandstone, Shale and Conglomerate that the surface of it in this basin is 1926.30 hectares that gully formed in 25.15 hectares (26.48 percent) of these sediments. The next most sediment belongs to the age of Holocene (shows by Qt2) include the young Alluvial fan deposits and its surface in this area is 695.95 hectares and extension of gully in this level is 15.50 hectares (15.94 percent) of these sediments. The next sediments are related to the age of Holocene (shows by Qtl) and include light-red-brown Sandstone and mudstone. The surface area is 481.14 hectares and gully occurred in 7.25 hectares of it. And the next one is related to the Holocene age (shows by Qal) with the sediments of channel fill deposits that the surface of this sediment is 493.64 and extension of the gully is occurred in 3.25 hectares of it. The next is related to the age of Holocene (shows by Qt) that the sediments included Talus, Rock fall and Colluviums, and gully extent in 2.75 hectares of it. Another sediments are related to the age of Micene (shows by Ml) and include purple and red Marl, Gypsum, Shale and Salt and gully extension is equal 1.50 hectares in this level. And the last lithology of this basin that gully happened on it is related to the period of Oligocene (shows by Omq) with the sediments of Marly Limestone, Marl, few Gypsum layers, Oysters and Tuff layers. The gully expansion in this sediment is 0.75 hectares. There are six more geology periods in this region that no gully occur in their sediments as below:
• Upper Jurassic (shows by Jl) includes sediments of light-gray Limestone, bedded to massive partly Chert and dolomite.
• Initial and Middle Jurassic (shows by JS) includes sediments of Sandstone, Shale and thin Limestone.
• Final Cretaceous (shows by K2) that includes sediments of gray and bedded Limestone.
• Paleocene (shows by PEfsc ) sediments include Sandstone, red Conglomerate and Calcareous.
• Lower Eocene (shows by r) includes of Rhyolite-Dacite, yellow and pink acid Tuff.
• Eocene (shows by L) includes of Marly-Sandy gray and green Limestone, Nummulites and Oysters. Oyster fossils are easily visible on the ground in this area.
Table 1. Geology of Toroud basin and gully extension
Class of Lithology Extent of Class (hectare) Extent of Class % Gully Extent (hectare) Gully %
Em 2460.95 28.16 40.50 41.65
M2 1926.30 22.04 25.15 26.48
Qt2 695.95 7.96 15.50 15.94
Qtl 481.14 5.50 7.25 7.46
Qal 493.64 5.65 3.25 3.34
Qt 204.06 2.33 2.75 2.83
Ml 743.21 8.50 1.50 1.54
Omq 139.79 1.60 0.75 0.77
Jl 633.93 7.25 - -
JS 564.66 6.46 - -
K2 270.83 3.10 - -
PEfsc 69.77 0.80 - -
r 46.51 0.53 - -
L 9.75 0.11 _ _
Fig. 1. Geology of Toroud basin and gully erosion extension
• Regarding to this research the most gully land is located in the sediments of Tertiary and Quaternary periods. As above explanation the most sediment of the land that gully occurs are included Marl, Limestone, Sandstone, Shale, Conglomerate and young alluvial fan deposits that they are sensitive against erosion and easily move and erode.
The below table and map show the classification of geology in Toroud basin and also the surface of gully erosion extension in the lithology classes.
Soil texture also is very important to form and extent gully erosion. Physical specification of the soil has a big role on the erodibility. The most erodible soils are rich in loam and sand.
To take the profile of soil for testing 35 points selected in three gullies and each gully in four points of Head, Mid, End and Testifier. Testifier is a point of the profile that located in the same slope with the gully line, and land use must be similar, also the same shape but without gully erosion that take place about 20 meters distance from the main gully. And every point in different layers.
Table 2. Soil texture and appearance properties of gully 1
Gully 1 Texture Depth (meter) Width (meter) Shape
Head S.L S.C.L 0.80 9 Trapezoid
Mid SI.C.L 2 15 Trapezoid
End L.S 0.50 6 Trapezoid
Testifier SI_ SI.C.L - - -
The result of the soil test for 3 gullies are coming separately in the below graphs and tables. There are no number for depth and width of testifier in the tables, because as mentioned testifier is not gully formation and this point is chosen to compare with the soil type in the gully lands.
4.1. The texture of soil in gully 1
As it is shown in the below graph and table This gully is include more sand and silt. In Sandy soil water holding capacity is low and usually they are dry. In silty soils water permeability is low and water holding capacity is more than sandy soil. It doesn't have the Colloidal characteristics and will be tough after rain or irrigation. The below figure and table show the texture of the soil and appearance properties of the gully 1.
In this gully high amount of silt and Sand, also less Lime and Clay make the gully wider with less depth. These soils can wash and move easily. Fig. 3 shows the head of gully 1 that is 9 meters wide and 0.80 deep.
Fig. 2. Soil texture in gully 1
Fig. 3. The head of gully 1
4.2. The texture of soil in gully 2
The result of soil test shows that by increasing clay and loam, the gully is deeper; also lime is effective to make the gully bed wider and it makes more pipe and hole in the sidewall (Fig. 5 and 6). Clay is swelling with the water so water cannot absorb. Also it gets dry and warm later than other soils. The below figure and table are shown the soil texture and appearance properties of the gully 2.
Fig. 4. Soil texture in gully 2
In the gully number 2 high amount of Silt, Sand and Loam make the gully more wide and deep. The soil with high Lime can be washed and moved easily.
Fig. 5 and 6. Piping and hole in gully 2
4.3. The texture of soil in gully 3
In this gully the sidewall is mostly very sharp and it is very difficult passing through them or impossible in some parts of this gully. The shape of the gully in the head is V shape and in the middle and end is trapezoid. By the result Clay is swelling with the water so water cannot absorb into the soil and it makes dry and warm later than other soils. Loam also is important in erosion. The below figure and table are shown the soil texture and appearance properties of the gully 3.
140 120 100 80 60 40 20 0
Fig.7. Soil texture in gully 3
Table 3. Soil texture and appearance properties of the gully 3
Gully 3 Texture Depth (meter) Width (meter) Shape
Head C.L_ _ SI.C.L 4 3 V
Mid C.L 5 9 Trapezoid
End C.L_ L 0.50 4 Trapezoid
Testifier SI.C. _ SI.C.L - - -
In this gully there is a good combination to make erosion. High amount of Loam, Silt and lime make the gully deep and also wider in the middle as it is shown in the below picture.
Fig. 8: The middle of gully 3
5. Conclusion
The research on the lithology and soil type in Toroud basin is shown that most erodible sediments in this region are related to the age of Eocene and Miocene include Marl, Limestone, Shale, Sandstone, Conglomerate and etc.
Soil Texture- Gully 3
Head Mid End Testifier
The high amount of gully surface is related to the Eocene period include Marl, Marlstone, Limestone and Tuff that is equal 41.65 percent of whole gully erosion in this region. The second is related to the age of Miocene include Sandstone, Shale and Conglomerate equal 26.48 percent of gully land in the area. The third most gully formation is related to the sediment of Holocene age include young alluvial fan deposits equal 15.94 percent of gully in Toroud basin. The less sediment of gully land is related to the age of Oligocene include Marly Limestone, Marl, few Gypsum layers, Oysters and Tuff layers, that is equal 0.77 percent of gully formation in this basin. The rest of the geologic period related to this area are included upper Jurassic, middle Jurassic, Upper Cretaceous, Paleocene, lower Eocene that there is no gully formation in the sediment of these ages. So the sediment of Tertiary and Quaternary are highlight in gully erosion formation in Toroud basin.
The result of the soil test in Toroud basin shows that the land with low clay content is more erodible. Clay with less permeability is more stable by the comparing with silt, sand and loam. So according to this research silty and sandy soil are very weak to erosion and the gully in this structure of the soil is more wider but short wall side. And the structure with more lime has more pipping and collapse from wall side.
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