Estimation of erosion caused by ephemeral gullies with EGEM model in Lanbaran basin, Ahar Chay

Estimation of erosion caused by ephemeral gullies with EGEM model in Lanbaran basin, Ahar Chay Abstract Gully erosion is one of a variety of geomorphic phenomena. Every year, this phenomenon causes lots of damage to agricultural land, rangeland and roads. Identifying the causes and modeling it play an important role in the management of catchment areas. One of the types of gully erosions is the ephemeral gully erosion. Currently, the only model that can assess this type of erosion is the EGEM model. Therefore, the study area has been observed since 2008 after rainfall. The data needed to implement the EGEM model was collected. SPSS and Excel softwares were used for quantitative analysis. According to the analysis of the measured parameters and the results of the model, the highest correlation coefficient exists among the estimated and measured depth, cross-sectional area, volume and width with the corresponding correlation coefficients of 0.849, 0.845, 0.818 and 814/0. Keywords: ephemeral gully – Lanbarn – Ahar Chai - EGEM model Introduction One of the most important types of erosions is gully erosion. This type of erosion causes significant changes in agricultural lands in arid and semi-arid regions of the world, and has harmful economic and social consequences (Esmaeiliy et al., 2015). (Kheir, et al., 2006; Marker, et al., 2008; Desmet, et al., 1999). Gully erosion is among the most important and complex types of erosion for the control of which the effective factors need to be identified (Ahmadi, 2011; 243). Gully growth is often considered as a major measure of environmental change, because its growth is not rapid and is not a common cause of erosion (Bayati Khatybi; 2004; 54). And because of the concentration of water flow in small grooves, a large volume of fine grains can easily be displaced in a short time due to ghost erosion compared to other erosion factors (Ryan, 2010; 288). According to Poesen, the gullies are channels with a cross-sectional area of more than 929 centimeters. Of course, this term was first used by Hughes in 1977 (poesen; 2003; 94). This type of erosion causes a sharp decrease in soil fertility and the production of abundant sediment loads. Sedimentation on the path to human structures and their destruction are among the effects of this type of erosion (Esmaeiliy et al., 2015). Recent field-based studies in Europe have evidenced annual soil losses due to EG erosion ranging between 2 to 90 m3 hectares. (Poesen et al., 1996; Casal´ı et al., 1999; Capra and Scicolone, 2002; aygarden, 2003; Valca´rcel et al., 2001). Material and Methods The sub-basin of Lanbarn is located on the eastern side of the Aharchay River. The area of this sub-basin is 20118 hectares and it is considered as the main stream of the Aharchay river. The basin was fielded between 1378 and 1395 after rainfall. There occur ephemeral gullies in this area in autumn, summer and spring, especially with heavy rainfall. Therefore, to study the ephemeral gullies, the required parameters were collected from 70 ephemeral gullies. To collect the data, field observations, GIS software and a GPS device were used. GIS, Excel and SPSS softwares were also used for processing. Results and discussion According to the results of the model, the highest correlation coefficient was observed among estimated and measured depth, estimated and measured cross-sectional area, estimated volume and measured volume, and estimated and measured widths. Therefore, the model predicts the cross-sectional area, the volume and the width of the ephemeral gullies efficiently. Also, regarding the effect of morphometric characteristics of the gully, the area of the basin, the width, watershed length and concentrated flow length of the ephemeral gully play the most part in soil erosion. The depth and cross section of temporary gullies have the least impact on erosion. Conclusion - Ephemeral gullies in this area are mostly formed in agricultural land. The intensity of rainfall, the expansion of communication routes and the burning of vegetation play an important role in the development of ephemeral gullies. - The standard version of the EGEM model can be used in the catchment area of Lanbarn. - To achieve optimal results, this model should be used in other climatic regions of Iran. - In this basin, the drainage area, width, watershed length and concentrated flow length of gully play the most part in soil erosion. - The depth and cross section of ephemeral gullies have the least impact on the eroded soils in this area. - - - - - - - - - - - - - - - - - - - -- -- --