Investigation of composition and evolution of clay minerals in floodwater spreading stations (A case study: Gachsaran floodwater spreading station)

To assess clay mineral compositions and the possible effect of floodwater spreading on the change of clay mineral types in the Gachsaran floodwater spreading station, samples were first selected from the control and floodwater spreading fields. Subsequent to sample preparation through X-ray, the clay minerals were determined carefully. According to the results, a number of clay minerals including Illite, Chlorite, Kaolinite and also swelling Smectite were identified in this area. Regarding all the samples, there were no significant differences in abundance of clay minerals, while some negligible differences were detected in the value of Illite and Smectite in relation to the control field samples; In fact, the amount of Illite and Smectitein of all samples were five percent more and lesser than that of control, respectively. In addition, at least 30 percent of the clays were Smectite. Therefore, after each flood in shallow sections and even in deep ones, Smectite clays swell immediately; that it can severely affect the soil permeability and subsequently a double effect on reducing water penetration. Such phenomenon can result in a number of remarkable problems in achieving the goals of floodwater spreading systems. Significant amounts of Illite clay showed that soils of the region under study were somewhat youth and in primary evolution. Although the possibility of structural changes of minerals in the floodwater spreading networks is theoretically expected to take place potentially, Gachsaran floodwater spreading station appears to have no significant effect on creating new clay minerals.