Restoring Hydrology

If not state otherwise, the text in this chapter is derived from: Convention on Wetlands. (2021). Global guidelines for peatland rewetting and restoration. Ramsar Technical Report No. 11. Gland, Switzerland: Secretariat of the Convention on Wetlands.

The first step in restoring degraded peatlands is the restoration of a peatland appropriate hydrology. To stop the degradation of peat, the water table should be increased in such a way that most, if not all, peat is submerged. To stimulate the formation of new peat, the water table should then slowly increase and follow the surface elevation caused by peat formation. This way the water level is always in a narrow range around the surface level.

The easiest way to increase the water table is to block drainage ditches and canals. To do this, all the canals, ditches, and even subsurface drains need to be identified. This can be done using LiDAR, aerial, or satellite imagery. Talking with local authorities, landowners, and farmers, as well as consulting historical maps, can increase the understanding of the local hydrology. The subsequent damming and blocking of ditches and canals will not only raise the surrounding water tables, but also re-establish surficial and overland flow, as well as reducing flow velocity to avoid erosion.

If there is a slope in the terrain, damming should start in the highest point and should work successively down. Ideally, the differences in the water table up- and downstream should not exceed 30 cm to reduce water pressure. This often requires a cascade of smaller dams to ensure an even increase in water table. In more levelled areas, less dams are needed to ensure a uniform water table increase.

Where possible, local materials should be used for drainage blocking and dam construction. Peat is a good material for building dams that is readily and locally available if conditions are not too wet (weak peat), too dry (peat breaks down), or too steep (peat erodes). In these cases, other materials, such as wood, metal, plastic, or brash or heather bales can be used. The decision tree below by Landry & Rochefort (2012), provides a helpful tool for deciding which technique and material should be used for drainage blocking, although other options might be present in specific situations. 

Water may also be lost from a peatland by vertical seepage into an aquifer or by losses to surrounding areas due to large differences in hydrology. Vertical leakage especially arises when agricultural drainage or de-watering for quarrying have substantially lowered the groundwater head, or when peat removal decreased the vertical resistance in the peatland. Areas that suffer from strong vertical leakage can be clogged by bringing in impermeable material such as peat, clay, or bentonite. If this is not enough, the water table in surrounding areas needs to be increased as well in order to maintain higher hydraulic heads. This can be attained by creating hydrological buffer zones around the peatland that decrease the difference in hydraulic head between the peatland and the surrounding area.