Classification and determination of erodibilty index of Marl formations in Tehran province

Marl units produce the highest amount of sediments among the lithological units in the watersheds, so they cause damages to the dams, power plants, floodgates, produce sediments in water channels, and cause death of aquatic animals, etc.Understanding erodibility of marls and classification of these units according to erodibility can help in soil conservation projects. In this study, for comparison of marl units from erosion point of view in Tehran province in two region: arid climate (Ivanaki basin, east of Varamin twon, Siahkouh of Garmsar, Eshtehard area and Hasanabad twon and etc), humid climate (Taleghan and Latian dam basins) two kind portable rainfall simulator was used. The result of each region as follow.In Ivanaki and arid region the amount of runoff and sediment of each marl unit (in three repeats) was measured. Then by using multiple linear regression, a relationship was found between physicochemical properties of marls (independent variables) and their sediment values (dependent variables). In this respect, characteristics such as SAR, EC, K showed respectively 89, 3.5, 1.5 percent of sediment production variation of different marl units. Analysis of variance of sediment data divided the marl units into four following groups: Group A (consisting of OLs unit) B, (consisting of M3 unit) C, (consisting of M1, M2 units ) and D, (consisting of O-M , OLg units) , erodibility of which decreases from A to D respectively. Then the physicochemical characteristics of four groups were studied by variance analysis which shows that SAR, Cl, Na, K, EC of these four groups are significantly different at 0.05, 0.01 and 0.001 levels.In order to compare physicochemical properties of various erosional features, T test was performed. The test results showed that factors such as Cl, EC, SAR, SO4, K of three erosional features ie: sheet, rill, and channel erosions, are significantly different at 0.05 and 0.01 level.The results of X-ray diffraction analysis of 27 marl samples showed that the amount of expandable clay minerals (montmorillonite and vermiculite) is higher in more erodible marls which are Lower Red Formation(OLs, OLg) and Upper Red Formation (M1, M2, M3) and this is in accordance with higher sediment yield from these units. But this trend is not found in EK and O-M marl units.For the purpose of classification of the marls with respect to their age and source of occurrence, an analysis of principle components was conducted on their main oxides and secondary elements. The above analysis successfully separated four formations which are different from the view point of age and source of occurrence. These are: Kond Formation (K.F), Lower Red Formation (L.R.F), Qom Formation (Q.F) and Upper Red Formation (U.R.F). But this method did not give good results for the main oxides.The results of analysis of variance of main oxides and secondary elements showed that the following elements are significantly different at 0.05 and 0.01 levels in four groups: Mn, Ti, Nb, Cr, V. But none of the main oxides of four groups showed considerable differences.In Iran, fine grained formations (Neogene units) are very susceptible to erosion. Also, they are the units producting runoff and csusing soil losses in watersheds. In Taleghan dam basin first Neogene units were separated to five subunits including Halite siltstone(NgSiH), Siltstone(NgSi), Mudstone(gy1C), Gypsum mudstone(gy1CG) and Halite claystone(gy2CH), based on physical and chemical properties. Then runoff and sediment rate was determinated in each subunits at two intensities (6 and 12 mm/M) using rainfall simulator. Analysis of variance and Duncans tests showed that NgSiH subunit has produced the highest amount of runoff and sediment rates and then the other of runoff and sediment rates of other subunits from highest to the lowest amounts are as follows: NgSi, gy2CH, gy1CG and gy1C are 5% significant level. The trend of induced runoff and sediment rates at different times showed that NgSiH and NgSi subunits runoff amounts were fixed rapidly at 2nd ten minutes. Also, on the other subunits, runoff amounts were fixed at 3rd ten minutes but sediment yield was increased rapidly at 3rd ten minutes. Factor analysis method was used to select the independent parameters.