A significant proportion of tropical peatlands has been drained for agricultural purposes, resulting in severe degradation. Hydrological restoration, which usually involves blocking ditches, is therefore a priority. Nevertheless, the influence of ditch blocking on tropical peatland hydrological functioning is still poorly understood. We studied water-level dynamics using a combination of automated and manual dipwells, and also meteorological data during dry and wet seasons over 6 months at three locations in Sebangau National Park, Kalimantan, Indonesia. The locations were a forested peatland (Forested), a drained peatland with ditch dams (Blocked), and a drained peatland without ditch dams (Drained). In the dry season, water tables at all sites were deeper than the Indonesian regulatory requirement of 40 cm from the peat surface. In the dry season, the ditches were dry and water did not flow to them.The dry season water-table drawdown ratessolely due to evapotranspirationwere 9.3 mm day À1 at Forested, 9.6 mm day À1 at Blocked, but 12.7 mm day À1 at Drained. In the wet season, the proportion of time during which water tables in the wells were deeper than the 40 cm limit ranged between 16% and 87% at Forested, 0% at Blocked, and between 0% and 38% at Drained. In the wet season, water flowed from the peatland to ditches at Blocked and Drained. The interquartile range of hydraulic gradients between the lowest ditch outlet and the farthest well from ditches at Blocked was 3.7 Â 10 À4 to 7.8 Â 10 À4 m m À1 , but 1.9 Â 10 À3 to 2.6 Â 10 À3 m m À1 at Drained. Given the results from Forested, a water-table depth limit policy based on field data may be required, to reflect natural seasonal dynamics in tropical peatlands. Revised spatial designs of dams or bunds are also required, to ensure effective water-table management as part of tropical peatland restoration.

Many tropical peatlands are subjected to artificial drainage that leads to degradation.Hence, hydrological restoration has recently been prioritized. Nevertheless, as field monitoring data are limited, little is known about how restoration measures, such as ditch dams and bunds, can regulate tropical peatland water tables. We used a hydrodynamic model -DigiBog_Hydroto simulate the effectiveness of ditch dams and bunds across three El Niño-Southern Oscillation (ENSO) scenarios, which are El Niño, La Niña and Neutral, in three typical sites. The sites were moderately degraded (Mod-Dgr) and severely degraded (Sev-Dgr) peatland plots (each 0.2 km 2 ), representing typical peatland conditions in Sebangau National Park, Kalimantan, Indonesia. Our fine-scale (1 m  1 m spatial resolution) modelling revealed that in the dry season of any ENSO scenario, the significant effects of ditch-dams alone on peatland water-level were limited to lateral distances of 26 m (in Mod-Dgr) and 12 m (in Sev-Dgr) from the ditch. In the dry season of an El Niño year, the combination of ditch dams and bunds helped maintain water levels up to 72 cm (in Mod-Dgr) and 69 cm (in Sev-Dgr) higher than in the no-restoration condition. During the extremedry period of an El Niño year, the bunds reduced the number of days when the water table was deeper than 40 cm in Mod-Dgr and in Sev-Dgr by 50% and 73%, respectively. We suggest that bunds used in combination with ditch dams are a practical restoration measure for tropical peatlands, providing critical extra water storage and helping maintain water tables near the peatland surface in dry periods. We also demonstrate how fine-scale hydrodynamic modelling is beneficial for planning and assessment of restoration measures in tropical peatlands.

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