Document Type : مقاله پژوهشی
Authors
Abstract
1. Introduction
Piping is a subsurface form of erosion which involves the removal of subsurface soils in pipe-like erosional channels to a free or escape exit. Although it is one of the coolest and rarest Erosion phenomena that can be formed in any weather conditions, but generally it develops in geological formation with low infiltration capacity and high soluble minerals. Piping materials are commonly highly erodible. However the situation is not fully understood, especially in terms of geomorphology. Compared with surface soil erosion by water, subsurface erosion (piping) is generally less studied and harder to quantify. However, wherever piping occurs, it is often a significant or even the main sediment source (Verachtert et. al., 2011). This erosion process might occur at any crack that exists in the earth structure, due to differential settlements, seismic movements, tension stresses, or holes caused by dry roots or gnawing animals (rabbits, rats, and etcetera). The erosion starts at any point where the seepage water discharges and works toward the reservoir, gradually enlarging the seepage channel. Field scientists studying badland processes in Mediterranean and Semi-arid climates require assurances that the material in which gullies are presented is not dispersive (Faulkner, 2010).
Piping materials are commonly highly erodible. Factors that are involved in Piping formation may include several categories. They are divided to bedrock, soil, climatic and biological factors. Material properties have a significant effect on erosion. When soils are dispersive, piping is very frequently a significant geomorphological agent. To fully interpret badland form and function in rapidly erosion Mediterranean and semi-arid climatic contexts, therefore, field scientists embarking upon any investigation into the gully processes involved require assurances that the material in which the gullies are presented is not dispersive (Faulkner, 2010).
Piping can be responsible for accelerated subsurface sediment transport. Subsurface piping pathways can extend for some distance as either continuous features or as a system of interconnected features that form extensive, branched networks. As the pipe enlarges, flow in the conduit becomes increasingly concentrated and turbulent. Collapse of these subsurface conduits and networks can lead to the development of karst-like (“pseudokarst”) topography (ZIEMER, 1992:188, after Halliday, 1960) and the development of gully networks (ZIEMER, 1992:188, after Higgins, 1984; Swanson et al.,1989).
‘‘Internal erosion’’ is similar to backwards erosion piping in that tractive forces remove soil particles. However, internal erosion is due to flow along pre-existing openings such as cracks in cohesive material or voids along a soil-structure contact. By this definition, internal erosion is not due to the dynamics of intergranular flow and the hydraulics of the problem is quite different than for backwards erosion (Lane, 1934).
Soil piping is an important, but little studied. Piping must be understood in order to design for environmentally sound land use. Research that has been done, are stressed mainly on surface erosion and the dynamics of water in the gully. Recent studies indicate that (1) gully erosion represents an important sediment source in a range of environments and (2) gullies are effective links for transferring runoff and sediment from uplands to valley bottoms and permanent channels where they aggravate off site effects of water erosion (Poesen et.al. 2003:51). The study of erosion forms in marls demonstrated that is a drift relationship between erosion forms and some soil chemical properties and includes different sort of erosion (Esmaeilzadeh, 2002).
North of Oman Sea is located in the Makran region, this zone is composed of seabed sediments, sediments of surface waters and ophiolites. During Eocene to Oligocene, South Makran coverd by the high thickness of flysch type sediments (Alaee Taleghani, 2003). Badland hills are the major part of Makran Flysch formation at Sirik and Jask County; the main geomorphologic forms of these foothills, is Piping (Fig 1). The aim of this study is to find out Piping erosion in Makran Flysch formation is affected from which of sediment characteristics at Sirik and Jask County.
2. Study Area
The study area is located at 25o38’-26o23’N 57o4’-58o7’E, in Sirik and Jask County, Hormozgan Province, south of Iran at the north of Oman Sea (Fig 2). In general the region under research could be assumed a dry land with very low rain. From geological aspect, this area affected by Makran region general construction and mainly composed of shale, marl and sandstone layers. The formation of this region began on Tertiary (Neogene) and has been continued in the Quaternary period. The geological structure of this area is mainly east-westward and it is located in Coastal Makran sub division that mainly composed of marl.
In this region abundance of blinded holes has led to Piping erosion on green marl sediments in Makran flysch formation. Piping erosion has more extensive in areas where marls sediment thickness increases (Fig 3).
3. Material and Methods
Research data were including sediment characteristics such as lime and gypsum percentages, calcium, magnesium, sodium and potassium levels, pH, Ec, soil texture and type of clay minerals. Maps of geology and topography, Satellite Imagery, Aerial Photos, laboratory equipment and computer software such as ILWIS, ArcGIS and Minitab also were used as a tools.
The methods can be divided into several sections:
A) Geomorphologic studies: Distribution map of Badland hills with and without Piping erosion was determined by using of available documents and expedition results.
B) Choosing the sediment sampling sites: With the help of networking, samples sites (20 controls and 30 samples), were identified in landforms map. Then, given the limits of costs, 4-5 points were randomly assigned in a manner that could be statistically processed.
C) Sampling: Sediment sampling was conducted by referring to the field. Before sampling, in order to mitigate the effects of climatic factors, 15 cm of the surface layer were taken aside.
D) Laboratory works: Sediment samples were transferred to the laboratory and characteristics such as lime and gypsum percentages, calcium, magnesium, sodium and potassium levels, pH, Ec, soil texture and type of clay minerals were identified.
E) Statistical analysis: Laboratory results analyzed with appropriate statistical test data in Minitab program.
4. Result and Discussion
Sediment characteristics of controls and samples such as lime and gypsum percentages, calcium, magnesium, sodium and potassium levels, pH, Ece and soil texture were obtained from the laboratory results. These characteristics were statistically analyzed and compared.
According to result:
1. Piping erosion is related to pH, Ece, clay, silt and sand percentage, lime percentage and calcium, sodium and potassium ions, at the significant level of %1.
2. Piping erosion is related to gypsum percentage and magnesium ion at the significant level of %5.
3. The electrical conductivity (Ece), silt and sand percentages, lime and gypsum percentages, magnesium, calcium, sodium and potassium ions, are directly related to Piping.
4. Soil pH, soil saturation (sp) and clay percentages, are inversely related to Piping.
Among sedimentological characteristics which studied in Makran flysch formation, the electrical conductivity of soil, silt, lime and gypsum percentages, also magnesium, calcium, sodium and potassium ions have been led to Sensitivity and soil acidity (pH), soil saturation percentage (SP) and clay percentage have been led to resistance from Piping.
5. Conclusion
The present study in the Sirik and Jask county area, Hormozgan province, Iran, shows that electrical conductivity, clay, silt and sand percentage, also calcium, potassium, sodium ions and lime percentage, ordinarily are the most affective factors on Piping erosion. In the next ranks, it affected by gypsum percentage and magnesium ion content. Among these factors, electrical conductivity, silt, lime and gypsum percentage, also magnesium, calcium, sodium and potassium ions have been led to Sensitivity and soil acidity (pH), soil saturation percentage (SP) and clay percentage have been led to resistance from Piping.
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