Promising Pilot Study on Countering Soil Subsidence

When peat decomposes, carbon dioxide is released, and soil subsides. In the Netherlands there are many peat soils, including in the Bloemendaal Polder. Here, the groundwater level can drop substantially during dry periods. Oxygen can then penetrate the peat, leading to faster decomposition and more greenhouse gas emissions. Measures can be taken to keep the peat moist and minimize soil subsidence.

A water expert doing monitoring work in an open landscape during winter

Field work in Polder Bloemendaal

Key Takeaways

Extra water was infiltrated into the soil during dry periods and drained during wet periods. This was achieved using a drainage system with remotely controlled sluices,
During the extremely dry summer of 2022, it was possible to keep the peat moist. Peat decomposition slowed down and greenhouse gas emissions were reduced. The effect of infiltration was smaller during the wet years of 2023 and 2024.
Infiltration into the pilot plot prevented soil subsidence and retained up to 70 cm more water as compared to the reference plot.
The higher groundwater level led to lower carbon dioxide emissions in 2022, but to slightly higher methane emissions. Net greenhouse gas emissions on the pilot field were ~3.8 tons of CO2 equivalent per hectare lower.

Project Details

Started: 2022 – Completed: 2024
Ref: 211282 | Status: Completed
Project title: Polder Bloemendaal Pilot Project Soil Subsidence

Background

Aiming for preservation of the Dutch peat meadow landscape by reducing soil subsidence, the Weids Bloemendaal Foundation set up a trial to test a measure that counters peat decomposition and soil subsidence.

In this pilot Acacia Water investigated how active groundwater management can help slow down peat decomposition and reduce greenhouse gas emissions.

Activities

During the pilot, water levels were controlled in the pilot field by infiltrating and draining ditch water via underground drainage pipes. This system works with remotely operated sluices. When they are open, water flows from the ditch to the drainage pipes. This allows extra water to be added to the soil during dry periods (infiltration) and excess water to be drained away during wet periods (drainage).

The drainage system is a special type of passive water infiltration system (PWIS), in which the drains are directly connected to the ditch. This allows the groundwater level to be managed more precisely than in the case of a completely passive system.

Drainage was installed on the west side of the selected field in the Bloemendaal polder in the second half of 2021. No drainage was installed on the east side, but hydrological measurements were done to compare the effects of the measure on the pilot field with the ‘normal situation’ on the reference field.

Acacia Water conducted measurements of the groundwater levels and the composition of the water in the soil. The amount of water flowing in and out of the pipes was measured by Broere Irrigatie. Greenhouse gas emissions (CO2 and methane) were measured by Ko van Huissteden of V.O.F. Kytalyk Carbon Cycle Research using a model from VU University Amsterdam (Peatland-VU) to calculate CO2 and methane emissions. Methane can form in peat at high groundwater levels and, per gram that’s emitted, it contributes more to global warming than an equivalent amount of CO2.

Findings

The installed drainage system was shown to work well in preventing groundwater levels from dropping too much during dry periods. The system’s greatest effect was seen during the driest measurement year (2022): groundwater levels on the test field were up to 70 cm higher than on the reference field.

However, there were slightly higher methane emissions on the pilot field. The difference between the reference field and the pilot field was approximately 3.8 tons of CO2 equivalent (combination of emitted CO2 and methane) per hectare, with higher emissions on the reference field.

On the pilot field, the system kept the top of the peat moist enough. Oxygen did not penetrate the peat and peat decomposition remained minimal. On the reference plot, where no water was added, the peat also remained reasonably moist, but wide and deep cracks appeared later in the summer, where oxygen could penetrate the peat.

In the wetter years of 2023 and 2024, the differences in groundwater levels between the pilot field and the reference field were much smaller. As a result, there was almost no difference in the modelled emissions between the two fields in those years. The reduction in greenhouse gas emissions was therefore highly dependent on the weather, with the greatest effect occurring in the driest measurement year.

It is likely that the tested drainage system helps to reduce soil subsidence.

Project Area

The peat soil in Polder Bloemendaal near Gouda is a typical example of the peat soils that are often found in the west of the Netherlands. The top layer of the soil, the topsoil, is approximately 45 cm thick. This layer consists of a mixture of clay, silt, sand, and urban waste and has been spread on the land since the Middle Ages . The topsoil covers the peat. Groundwater levels in this area are usually high, but during dry periods, the groundwater can drop up to a meter below surface level. Measures can be taken to keep the groundwater at a higher level. This helps to reduce peat decomposition, and thus CO2 emissions. Currently, this type of soil is mostly used for agricultural practices, including livestock farming and grass harvesting.

Geographic scope: local

Downloads and Links

Publiekssamenvatting Proef tegen bodemdaling polder Bloemendaal veelbelovend (Dutch only)

Download

Eindrapport Hydrologische Analyse Bloemendaal (Dutch only)

Download

Integrale eindrapportage pilotproject bodemdaling polder Bloemendaal (Dutch only)

Download

In Cooperation With

Contact

Projects

Nature-based Solutions for a Climate-Resilient Geul River Valley

Acacia Water, Belgium, Bureau Stroming, H+N+S, Business unit, Country, Germany, Natuurkracht, Netherlands, Water security

Nature-based solutions (NbS) can reduce the likelihood of droughts and floods. For the river basin of the Geul in the Netherlands, Belgium, and Germany, the effects of 10 landscape interventions were modeled using the SWAT+ model (Soil and Water Assessment Tool Plus).

Enhancing Flood Resilience in South Sudan

International Organization for Migration (IOM), South Sudan, Water security

South Sudan has faced prolonged and severe flooding for over many years, To strengthen the communities’ resilience to climate-related disasters, a feasibility assessment was conducted, identifying robust, evidence-based, and community-informed investments.

Water Harvesting in Jordan: Building Resilience Through 3R

Jordan, Water security

Targeting Jordan’s northern regions, critical water challenges posed by climate change, population growth, and human security risks are addressed. This is done through rainwater harvesting, flood risk reduction, groundwater recharge, and reuse strategies.

Promising Pilot Study on Countering Soil Subsidence

Key Takeaways

Project Details

Background

Activities

Findings

Project Area

Downloads and Links

In Cooperation With

Commissioned by:

Funded by:

Project partners:

Contact

Tessa van Hateren

Related topics:

Projects

Contact

Regional office