Water-table responses to storms in forested, drained and ditch-blocked tropical peatlands, Sebangau, Kalimantan, Indonesia

The effects of hydrological restoration, usually using ditch dams, on water-table responses to storms in drained tropical peatlands are poorly understood. We collected hourly rainfall and water-level data during the dry and wet seasons (August 2019 to January 2020) at a forested peatland (Forested), a drained peatland with ditch dams (Blocked), and a drained peatland without ditch dams (Drained) in Sebangau National Park, Indonesia. Hydraulic conductivity of the surface peat and bulk density of the peat profiles were also measured. The two main components of a Principal Component Analysis (PCA) could explain 62 % to 68 % of the variation of water-table responses to storms at the study sites. The responses were related to the initial water table, the depth and the duration of the storm, and the position within a site with respect to ditches. In Forested, the mean of the post-storm water-level drawdown speed (DSpeed) was 0.039 cm hour-1 (SD = 0.024 cm hour-1) when the water table was deeper than 50 cm below the surface but 0.047 cm hour-1 (SD = 0.039 cm hour-1) when within the upper 50 cm. In Drained/Blocked, DSpeed varied greatly with depth, distance to ditches, and distance to the main outlet of ditches. Ditch dams alone may not recover the water-table responses to storms in drained tropical peatlands when compared to more intact forested systems.