JWSS - Journal of Water and Soil Science

Nowadays application of soil conditioners for mitigation and reduction of runoff is a current method. Considering the advantages of Polyacrylamide (PAM), this study was arranged to evaluate impacts of this soil conditioner on soil infiltration rate, runoff and erosion control. To fulfill the goal, a factorial experiment in a completely randomized design was carried out with four PAM treatments (0, 6, 10, 20 kgha^-1), three slope levels (3, 6 and 9 %), three irrigation treatments and three replications. Surficial (0-10 cm) soil samples were collected from Shahrekord University campus and poured into square plots (55×55cm) with 15 cm depth, after pretreatments. The plots were treated with a simulated rainfall intensity of 36 mm.h^-1 for 15 minutes and the attributed runoff, sediment load and drained water were collected and measured. The results showed significant differences among the runoff and soil erosion of control and of PAM treated soils. PAM minimized the raindrop negative impacts on soils and improved water infiltration and diminished the attributed runoff. Soil treatment with PAM as a soil conditioner significantly reduced soil erosion and sediment yield in all treatments.

In the present study, CanESM2 climate change model and stormwater management model (SWMM) were employed to investigate the climate change effects on the quantity and quality of urban runoff in a part of Karaj watershed, Alborz Province. The base period (1985-2005) and future period (2020-2040) are considered for this purpose. Based on the existing main and lateral drainage system and to be more accurate, the watershed was divided into 37 sub-watersheds by ArcGIS software. To simulate rainfall-runoff, the intensity-duration-frequency (IDF) curve has been prepared for a 2-hour duration and 10-year return period, for the base period and RCP2.6 and RCP8.5 climate change scenarios based on the obtained precipitation data from Karaj synoptic station. Results showed that mean 24-hour precipitation values in RCP2.6 and RCP8.5 scenarios will increase by 21% and 11%, respectively, and maximum 24-hour precipitation values will decrease by 17% and 23%, respectively, as compared to the observed values in the base period. Also, based on the results of quantitative and qualitative runoff modeling in the study watershed, and according to the outflow hydrograph in the RCP2.6 and RCP8.5 scenarios, the outlet runoff discharge will decrease by 5.8% and 7.1%, respectively. Also, the flooded areas in the watershed will decrease by 13% and 15.28%, respectively. The concentration of pollutants in the RCP2.6 and RCP8.5 scenarios, compared to the base period, including total suspended solids (TSS), will increase by 7.48% and 9.24%, total nitrogen (TN) will increase by 6.93% and 8.48%, and lead (Pb) will increase by 7.32% and 8.91%, respectively.