For the field trials with submerged drains and pump-controlled submerged drains (pressurised drains) that have been carried out since 2003, a statistical analysis has been carried out on measured groundwater levels (2004-2021) and grass yields (2004-2015). The statistical analysis yielded relationships for groundwater level to quantify the effect of submerged drains (whether or not pressurised) compared to a common situation without submerged drains. The effect of submerged drains was the same for the winter and summer half-year (linear relationship). Compared to submerged drains, pressurised drains gave extra infiltration in the summer half of the year (exponential relationship). Limiting factors for operation are inflow of polluted water, a too large drain distance and pressure loss at the moment the water level in the ditch and/or the supply control of pressurised drains moves in the same direction as the groundwater level. Grass yields were not or hardly influenced by submerged drains under fertilized conditions. Where submerged drains provided extra water infiltration during summer, the nitrogen supply from the soil was reduced. This yield-reducing effect was compensated by a higher nitrogen utilization (conversion of nitrogen from the soil and fertilizer into biomass). ; Voor de proeven met onderwaterdrains en pompgestuurde onderwaterdrains (drukdrains) die vanaf 2003 zijn uitgevoerd is een statistische analyse uitgevoerd op de gemeten grondwaterstanden (2004-2021) en de grasopbrengsten (2004-2015). De statistische analyse leverde voor de grondwaterstand relaties op om het effect van onderwaterdrains (al of niet pompgestuurd) te kwantificeren ten opzichte van een gangbare situatie zonder onderwaterdrains. Het effect van onderwaterdrains was voor het winter- en zomerhalfjaar gelijk (lineair verband). Drukdrains gaven ten opzichte van onderwaterdrains extra infiltratie in het zomerhalfjaar (exponentieel verband). Beperkende factoren voor de werking zijn instroom van vervuild water, een te grote drainafstand ...