Simulation of irrigation return flow from a Triticale farm under sprinkler and furrow irrigation systems using experimental data: A case study in arid region

Irrigation return flow is an important and hard-to-estimate component of the groundwater balance equation. In this study, irrigation return flow from a Triticale farm under sprinkler and furrow irrigation systems was investigated in arid region. For the sake of accuracy, high-resolution (both temporally and spatially) datasets were provided through ten monitoring wells (eight two-meter-deep and two six-meter-deep monitoring wells) equipped with totally 76 soil moisture sensors. Moreover, dual crop coefficient approach was used for estimation of evapotranspiration in each experimental field due to its adaptability with short-interval data. The datasets were used for calibration and validation of HYDRUS-1D software over about six months of Triticale growth period. The results showed an acceptable agreement between measured and simulated water content in each soil layer of furrow- (with RMSE and MAE equal to 0.035 and 0.031 cm³/cm³, respectively) and sprinkler-irrigated (with RMSE and MAE equal to 0.024 and 0.020 cm³/cm³, respectively) fields. HYDRUS simulations were also used for estimation of irrigation return flow. Results showed that in furrow-irrigated field, about 13.3 percent of inflows (including irrigation and precipitation) returns back to groundwater aquifer as irrigation return flow. However, that was negligible in sprinkler-irrigated field. The rationale behind different irrigation flows obtained for each experimental field was investigated using water balance components obtained by HYDRUS software. It was revealed that total water application depth and evapotranspiration was almost the same for both experimental fields. However, the intrinsic difference between the application intervals and in turn, application depths in each interval provoked more irrigation return flow in furrow-irrigated field. Eventually, sensitivity assessment was done to quantify the impact of soil hydraulic parameters on return flow. The results showed that the parameters which have the most impact on total amount of return flow are θs and n for furrow-irrigated field whereas in the case of sprinkler-irrigated field parameters showed inconsiderable impact on return flow. The fact which has root in different initial water content of each experimental field.