Performance assessment of subsurface drainage systems in the Harran Plain of the South‐East Anatolian region of Turkey

Abstract

The purpose of performance assessment of subsurface drainage systems is to achieve efficient and effective system performance by providing relevant feedback to the management of the drainage system at all levels. Therefore, it assists management in determining whether performance is satisfactory and, if not, what corrective actions need to be taken and where to rectify the situation. In this study, approximately 30% of the drainage systems built in the Harran Plain were monitored during one irrigation season in 2017. The fluctuation of the water table was measured daily at a total of 33 subcentres. In addition, electrical conductivity (EC) and pH values were measured by taking water samples from six collectors once a week. Drain flow measurements were carried out at three collector outlets. According to the SEW30 (sum of excess water at depths less than 30 cm) indicator, 82% of the monitored areas had good, medium‐good drainage and moderate drainage. The seasonal average water table depth of the monitored area was found to be approximately 120 cm. The data show the existence of a drainage system that creates an aerated soil layer suitable for all shallow‐ and deep‐rooted, water‐resistant, and sensitive plants in all of the monitored areas. Generally, the salinity of drainage water is much higher than that of irrigation water. This value was up to 25 times higher in some collector outlets. This finding has raised suspicions that salty groundwater is being pumped into the drainage system.