Investigation of bioengineering properties of Celtis caucasica and Pistacia atlantica in slope stabilization (Case study: Kalan Malayer Dam)

Soil erosion is a natural process that is intensified by human activities. Experts of natural resources consider soil erosion as a phenomenon that has caused the destruction of civilizations. Preventing erosion and actually reducing its damages to the natural level of soil losses depends on choosing appropriate strategies for soil protection. Preventing erosion and actually reducing its damages to the natural level of soil losses depends on choosing appropriate strategies for soil protection. Among the many methods of preventing soil erosion and increasing the stability of slopes, bio-engineering methods of protected areas have received a lot of attention due to environmental and economic issues in engineering today.

In this research, the effect of the root of Celtis caucasica and Pistacia atlantica in soil reinforcement around the Kalan Dam, 34 km southwest of Malair City, was investigated on different slopes. To carry out this study, two species of Celtis caucasica and Pistacia atlantica were investigated in three different populations in three areas with low (0-10 %), medium (10-25 %), and high slopes (25-40 %). The root samples were collected on December 15, 2021, from a depth of about 30 cm. In general, 6 individual trees were randomly selected in each area and all the characteristics of the soil were examined in 6 repetitions and the root in 10 repetitions (to test the tensile strength of the roots). The treatment used to preserve and prepare the roots includes washing and placing them in plastic bags containing a 15 % alcohol solution. Then samples with a length of about 10 cm were randomly selected and the speed of the tensile strength test was 10 mm min-1. The root was measured using a standard Instron device manufactured by the Santam factory. Considering the normality of the data, the t-test was used to compare the two species. Three harvesting areas with different slope classes, including low (Region 1), medium (Region 2), and high (Region 3) slopes. The treatment used to preserve and prepare the roots includes washing and placing them in plastic bags containing a 15 % alcohol solution. Then samples with a length of about 10 cm were randomly selected and the speed of the tensile strength test was 10 mm min-1. The root was measured using a standard Instron device manufactured by the Santam factory. Considering the normality of the data, the t-test was used to compare the two species. In three harvesting areas with different slope classes, including low (Region 1), medium (Region 2), and high (Region 3) slopes, 18 stems of Callaghan and 18 stems of P. atlantica were harvested for root Callaghan, and 18 stems of P. atlantica were harvested for root sampling.

The results showed that the root elasticity of C. caucasica is higher than P. atlantica. The relationship between the diameter and root reinforcement was different, and about C. caucasica it was negative. the highest root reinforcement is related to fine roots. The RAR (Root Area Ratio) in C. caucasica was higher on a high slope rather than a low slope. In steep slopes (Region 3) root tension of C. caucasica is higher than the area with the average slope. There was a positive correlation between PL and LL of soil in C. caucasica stand in Region 3. Finally, strengthen the soil and reduce erosion in the upper slopes. The noteworthy point is that the percentage of carbon in the soil in Region 3 is higher than in the other two regions, which is due to the negative correlation between carbon and sand in the soil. C. caucasica in high-slope lands with a lower percentage of sand causes an increase in carbon deposition and parameters of the dough limit and liquid limit of the soil. According to the results of the data, the amount of root elasticity of C. caucasica is higher than P. atlantica species. The relationship between diameter and root tension is different in the case of species. About C. caucasica it was negative and the highest root tension is related to the roots of the fine roots, but in P. atlantica, the relationship between diameter and tension is a positive power function and As the diameter increases, the amount of tension increases. The amount of root area ratio (RAR) in C. caucasica is higher on the higher slope than on the lower slope. The percentage of clay in the soil texture has a negative correlation with the amount of RAR, and root growth and distribution are less in clay soils. C. caucasica in high-slope lands with lower sand percentage increases carbon deposition and parameters of the plastic limit and liquid limit of the soil.

It is suggested to use species that increase soil reinforcement and reduce the amount of erosion in the area of the dam in order to reduce the amount of erosion and increase the useful life. according to the results, it can be recommended that it is better to use C. caucasica in afforestation around the Kalan Dam because of its greater effect in increasing soil improvement and reducing erosion.