Efficiency of old tile drain systems in soils with high clay content: differences in the trench backfill zone versus the zone midway between trenches.

摘要

This study was carried out in order to check the efficiency in water transport capacity in the trench backfill zone (IT) in 2-45-year-old tile drains, and the differences between IT and the zone midway between trenches (BT) in field-saturated steady-state infiltration rate (Ifs) and saturated hydraulic conductivity (Ks). At seven sites with high clay content, Ifs was recorded in situ in large rings (1 m diameter) and at the same time small cores (7.2 cm in diameter) were sampled to measure Ks in the laboratory. There were large differences in drainage efficiency between the disturbed trench backfill zone and the undisturbed zone midway between trench lines. Ifs and Ks values were in almost all cases larger in IT than in BT. Differences between the plough sole and subsoil, for both Ifs and Ks, were more evident in BT than in IT. The positive effect above the drainpipes, indicating that macropore connectivity was superior in IT, was evident for as long as 45 years after the installation of drainpipes. In BT, Ifs and Ks ranged within approximately equal values. In IT, however, Ifs ranged at larger values than Ks. In modelling these kinds of soils, it may be considered whether water transport during heavy rain events should be characterized by a quick onset of water flow in drainpipes caused by the more permeable soil in the backfill trench, and a subsequent slower and more continuous transport of water from the zone between trenches, and in what way the drain water quality is influenced by this..