Investigation of the Terraces of the Zayandeh‒rud River's Current Pathway Using the Harden's Profile Development Index (PDI)

One of the most important goals of the soil science is to investigate the changes in the earth surface systems in the past and useing their patterns to predict environmental changes in the future in order to improve land management. Therefore, this study was conducted on the current Zayandeh‒rud River’s pathway in a semi-detailed scale in order to understand the development of alluvial plain of the river.
Geomorphic surfaces were determined using a stereoscopic interpretation of aerial photos with a scale of 1:20000 and based on the Zinck’s hierarchical classification system. Fourty eight profiles were drilled at 1 km/km network, according to the common method of semi-detailed soil studies in a grid survey pattern. Soil classification was finalized in accordance with the Soil Survey Staff. The degree of soil evolution was studied according to Harden's soil development index (PDI) for eight control pedons.
According to previous studies, the Zayandeh-e-Rud River during its flow time lave had a single pathway three terraces in the Zayandeh-rud plain. The last research showed that the Zayandeh-roud River runs through three separate way over time. In this study, the interpretation of aerial photos and field study cleared that the current pathway of the Zayandeh‒rud River includes a series of three terraces, which each terrace consists of sub-terraces. Also it was found that Fourty eight profiles in this research were classified in four suborder (including argids, calcids, cambids and orthents) with eight soil families. On the other hands, the calculated PDI values for the control pedons of these eight families also were different. This indicated difference of degree of soil evolution in the current river’s paethway.
Therefore, it can be concluded that the soil of three terraces of the current the Zayandeh‒rud River’s way is more diverse than previously reported, and this variation indicates the difference in the age of these terraces. Pedologic study also revealed that the soils of the first terrace had the highest PDI and evolution. Presence of argillic and calcic horizons in these profiles confirms this conclusion. On the other hand, the soils in the second terrace also had a lower PDI index and less degree of development than the first terrace, and were more developed than third terrace’s soils. Therefore, it can be stated the curent pathway has three independent age terraces with multi-interior terraces. From the results of this study, it can be anticipated that also there are terraces on previous river pathway, which require more research to prove them.