Pressurized drainage can effectively reduce subsidence of peatlands-lessons from polder Spengen, the Netherlands

Abstract

Reducing soil subsidence caused by peat oxidation is a major challenge in the Dutch peatlands. To maintain suitable conditions for dairy farming water levels are periodically lowered to keep pace with soil subsidence. Consequently, soil subsidence continues, causing increasing water management costs. We experimented with pressurized drainage in Polder Spengen, a peatland polder in the west of the Netherlands that is primarily used for dairy farming. In this polder, surface water levels of 40 cm below ground surface are maintained, which results in average soil subsidence rates of 7mmyr-1. Pressurized drainage is a novel technique to reduce soil subsidence, it uses field drains that are connected to a small water basin. Surface water can be pumped in or out the water basin, which enables active manipulation of the pressure head in the field drains. The objective of this study is to implement this technique into practice and determine its effect on groundwater tables, soil subsidence rates, and water demand. We applied pressurized drainage in 55 ha of peatland meadows in Polder Spengen, distributed over seven farms. We monitored groundwater tables, surface elevation and water demand. Preliminary results show that during the extreme dry summer of 2018, groundwater tables could be maintained at 40 cm below ground surface, which is 60 cm higher compared to locations without pressurized drainage. This reduced soil subsidence by 50 %. Throughout the entire summer of 2018, the water demand amounted to 3- 5mmd-1. We believe the technique can effectively contribute to minimize soil subsidence, but relatively high implementation costs may be a barrier to large-scale implementation.