Modelling subsidence due to Holocene soft-sediment deformation in the Netherlands under dynamic water table conditions

Henk Kooi,Gilles Erkens

doi:10.5194/piahs-382-493-2020

Abstract

Abstract. Local and regional governments in The Netherlands are increasingly faced with the question how to adjust and optimize groundwater table conditions in urban areas to minimize ongoing subsidence and its consequences. To help addressing this question, a model was developed that includes soft-soil deformation by creep. In this paper, a study is presented in which the model was used to investigate and intercompare the effectiveness of measures that (a) prevent anomalous water table drop during a drought, (b) suppress the seasonal variability of the water table, and (c) involve a permanent rise of the mean water table.

Highlights

Urban areas in the western part of The Netherlands commonly show persistent subsidence over multiple decades at rates between 0–10 mm yr−1
In contrast to areas with peat oxidation, in urban areas, the persistent nature of the subsidence is thought to be the expression of viscous behaviour of the subsurface, under periodic addition of fill at the surface to compensate for elevation loss and/or water table lowering
Becausewater level change can provoke subsidence, and local and regional governments are responsible for groundwater levels in the public space, these governments are faced with the question how to adjust and optimize water table conditions to minimize the subsidence and its consequences

Summary

Introduction

Urban areas in the western part of The Netherlands commonly show persistent subsidence over multiple decades at rates between 0–10 mm yr−1. In contrast to areas with peat oxidation, in urban areas, the persistent nature of the subsidence is thought to be the expression of viscous behaviour (creep) of the subsurface, under periodic addition of fill at the surface to compensate for elevation loss and/or water table lowering. The subsidence causes damage to pipes and cables, damage to buildings and infrastructure without pile foundation, damage to buildings due to decay of wooden pile foundations if the water table is lowered, nuisance flooding, and high maintenance costs of public space functions. Because (ground)water level change can provoke subsidence, and local and regional governments are responsible for groundwater levels in the public space, these governments are faced with the question how to adjust and optimize water table conditions to minimize the subsidence and its consequences. To be able to choose among potential measures, questions they seek answers to include: How much subsidence can be prevented by: a. preventing excessive water table lowering during an occasional drought;

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Conclusion