Researchers from Utrecht University, TNO and Deltares have developed a new method to quantify and predict land subsidence caused by the compression of peat layers. This new application of existing technology can be used to determine and predict subsidence in deltas where subsurface information is currently sparse. They published their results in Geophysical Research Letters.

Peat areas are commonly present in deltas and are increasingly being submerged due to land subsidence. This phenomenon has inevitable high costs and harmful consequences such as increased flood risk and damage to housing and infrastructure. An important driver of land subsidence is the compression of peat layers caused by increasing overburden or the lowering of the water table.

Future peat compression

To tackle land subsidence resulting from peat compression, information about current compression levels is needed; this is essential to determine potential levels of compression in the future and the associated land subsidence. Detailed geological and mechanical information about the peat layers is therefore needed but this information is lacking in many subsiding deltas, and current monitoring methods primarily measure the vertical movement of the surface.

Cone Penetration Testing

Researchers from Utrecht University, TNO and Deltares found that an already existing method can acquire this kind of subsurface information: Cone Penetration Testing, or CPT. CPT measures certain mechanical characteristics of peat, and is one of the most widely used subsurface investigation techniques worldwide due to its relatively low operational costs, the international standardisation of the method, and digital logging of the results. Thousands of CPT measurements are stored in databases worldwide.

On reusing an already existing method Kay Koster, first author and geoscientist at Utrecht University and TNO says: “Subsidence in deltas is an urgent threat, but acquiring new data is expensive and time consuming, so we focussed on re-using existing measurements. CPT data is already abundantly available in deltas with peat in its subsurface.”

Generic application of the method

Gilles Erkens, land subsidence expert at Deltares and Utrecht University explains how they re-used CPT: “We correlated thicknesses of compressed peat layers in the Dutch delta to CPT-data, enabling the quantification and prediction of land subsidence by peat compression.”

The challenge addressed by this study was to use CPTs to quantify levels of peat compression in the past, and the potential for predicting future compression. Erkens: Subsequently we successfully applied these results to available CPT data of the Sacramento Delta in the U.S. and Kalimantan in Indonesia, emphasising the generic application of the method.”

Predicting land subsidence worldwide

Linking CPT measurements to land subsidence as a result of peat compression opens up a wealth of data that can be used to quantify and predict subsidence in coastal zones around the world. These data can be used to complement existing methods and will make it possible to predict land subsidence in coastal zones worldwide as a result of peat compression.

Publication

Koster, K., G. Erkens, and C. Zwanenburg (2016), A new soil mechanics approach to quantify and predict land subsidence by peat compression, Geophys. Res. Lett., 43, 10,792–10,799, doi:10.1002/2016GL071116.