• April 8, 2026

Best practices in closing and damming drainage ditches (Valley of the Grote Beek)

In the Valley of the Grote Beek, decades of drainage lowered groundwater levels, accelerating peat oxidation and weakening the natural hydrology of the alder swamp forest. Within LIFE Multi-Peat, restoring the hydrology of the Grote Beek Valley became a central priority. We therefore tested, refined and combined several drainage ditch blocking techniques, each adapted to local conditions, accessibility and best practices learned on the go. The lessons learned now form a set of tried-and-tested methods for ditch blocking in similar landscapes.

 

Filling ditches completely: infilling as the gold standard

Wherever possible, ditches were filled entirely. Using local peat from the ditch edges, we closed over 2.2 km of ditches without bringing in external material. This method removes the drainage channel altogether and restores the natural ground level. In places where soil was present but couldn’t be taken because of trails or access needs, we used sand from a nearby removed dike instead. This was only needed for some drainage ditches next to a hiking path. 

 

Peat-wood dams: the best option in dense forest 

A large part of the valley consists of alder carr, where machines simply cannot enter without cutting most of the forest. To avoid hauling materials through the swamp, we worked entirely with what the site itself provided. At first, we tried wooden pole dams: poles hammered into the peat with logs stacked between them. They slowed the water a bit, but never fully sealed the ditch. The real improvement came when we built peat–wood dams by using logs and peat found on site, often from invasive trees that needed to be removed anyway. With nothing more than a spade and a chainsaw, this low‑impact method allowed us to block 80 ditches, covering more than 7 km.

 

One method we won’t be repeating anytime soon is the sandbag era

Carrying hundreds of sandbags through knee‑deep and dense alder forest turned out to be a heroic but exhausting workout. And after all that effort, the bags themselves vanished within six months, leaving only piles of sand behind. Local wildlife loved them though. Boars and deer quickly adopted the sand dams as convenient crossing points, undoing our hard work in no time. A memorable experiment, but definitely not our most effective one.

 

A heavy-duty solution for a heavy-duty ditch 

One major drainage ditch, three metres deep and wide, will require a stronger approach. We will build a wood–clay dam using chestnut beams and bentonite clay, with two large peat dams upstream to slow the flow. This combination will create a stable barrier in a place where lighter techniques will not hold. 

 

Part of a bigger hydrological puzzle 

Closing ditches is only one part of restoring the valley’s natural water system. We also: 

• filled artificial ponds
• tackled woody encroachment on historically open peatland and strengthened the recovery by fully closing drainage ditches and other rewetting interventions
• removed artificial elevations and manmade structures
• will remove old, raised areas
• will relevel sections of the Grote Beek to reconnect it with its floodplain 

Together, these actions help to restore the peatland’s hydrology and might kick-start peat formation again. 

 

A landscape already responding 

Early monitoring shows wetter soils, reduced drought stress and even the spontaneous return of peatland specialist plant species. The valley is developing towards a functioning peatland once more. 

 

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