Quantifying local losses due to root intrusion in subsurface drip irrigation systems by monitoring inlet discharge and pressure head

In subsurface drip irrigation systems (SDI), the emitter flow rate is affected by the root intrusion phenomena and by the so-called back pressure that limits the buried emitters’ outflow. This paper suggests a methodology to investigate the effect of root intrusion and back pressure in SDI performance, for different root guard emitter treatments in a 6-year experimental campaign (2018-2023), carried out in Sicily (Italy). Inlet discharges and pressure heads were collected over time, and their variations were used to quantify the effect of root intrusion in terms of local losses. The change in the SDI hydraulic performance was studied using a modified Hardy Cross method (HCM), which is suitable for lopped drip irrigation networks. The HCM applications also considered local losses and back pressure, requiring a comprehensive hydraulic characterisation of the soil to estimate accurately the factors influencing back pressure. Specifically, the influence of root intrusion in different emitters was analysed by considering the time variation of the fraction α of the kinetic head. The results showed diverse behaviours among the root guard emitter treatments. Emitters treated with different herbicides (He 1 and He 2), revealed no significant α-fraction variation over time, denoting the effectiveness of He 1 and He 2 treatments in root intrusion protection. Whilst, for Copper (Cu) and control (Ctrl) treatments, a severe decrease in emitter flow rate was observed, confirmed by high α-fraction variations over the investigated period.