Comprehensive risk assessment of groundwater drawdown induced subsidence

Abstract

We present a method for risk assessment of groundwater drawdown induced land subsidence when planning for subsurface infrastructure. Since groundwater drawdown and related subsidence can occur at large distances from the points of inflow, the large spatial extent often implies heterogeneous geological conditions that cannot be described in complete detail. This calls for estimation of uncertainties in all components of the cause-effect chain with probabilistic methods. In this study, we couple four probabilistic methods into a comprehensive model for economic risk quantification: a geostatistical soil-stratification model, an inverse calibrated groundwater model, an elasto-plastic subsidence model, and a model describing the resulting damages and costs on individual buildings and constructions. Groundwater head measurements, hydraulic tests, statistical analyses of stratification and soil properties and an inventory of buildings are inputs to the models. In the coupled method, different design alternatives for risk reduction measures are evaluated. Integration of probabilities and damage costs result in an economic risk estimate for each alternative. Compared with the risk for a reference alternative, the best prior alternative is identified as the alternative with the highest expected net benefit. The results include spatial probabilistic risk estimates for each alternative where areas with significant risk are distinguished from low-risk areas. The efficiency and usefulness of this modelling approach as a tool for communication to stakeholders, decision support for prioritization of risk reducing measures, and identification of the need for further investigations and monitoring are demonstrated with a case study of a planned railway tunnel in Varberg, Sweden.

Risk Mapping of Groundwater‐Drawdown‐Induced Land Subsidence in Heterogeneous Soils on Large Areas

“…Although the criteria that define the extent of the risk area are reasonable, other percentiles and subsidence limits are possible. When a tolerability criteria is defined in a risk assessment for groundwater drawdown in subsidence‐sensitive areas, it should reflect the acceptance levels of affected stakeholders and norms and regulations in the society . Based on the tolerability criteria, safety measures can be suggested by means of value of information analysis; see, e.g., Zetterlund et al .…”

“…When a tolerability criteria is defined in a risk assessment for groundwater drawdown in subsidence-sensitive areas, it should reflect the acceptance levels of affected stakeholders and norms and regulations in the society. (9) Based on the tolerability criteria, safety measures can be suggested by means of value of information analysis; see, e.g., Zetterlund et al (49) For the planned City Link tunnel, the risk maps have been used for communication to stakeholders and authorities in the process for application for permit to drain groundwater in accordance to Swedish legislation.…”

“…The suggested method in this study is limited to the third (pore pressure) and the fourth (subsidence) part of the chain. For a risk assessment of the whole cause–effect chain, the method needs to be combined with estimations of groundwater‐drawdown magnitudes, sensitivity of constructions founded on the compressible deposits, and costs associated with the potential subsidence damages …”

“…For a risk assessment of the whole cause-effect chain, the method needs to be combined with estimations of groundwater-drawdown magnitudes, sensitivity of constructions founded on the compressible deposits, and costs associated with the potential subsidence damages. (9,10) The large spatial scale of the problem domain implies heterogeneous soil conditions formed by geological processes and anthropogenic activities such as construction, excavation, filling of material, and groundwater drawdowns. Therefore, the subsurface cannot be described in detail without extensive and costly site investigation programs.…”

Being Bayesian: Discussions from the Perspectives of Stakeholders and Hydrologists

“…For those of us who spend time thinking about how hydrologic models can and, perhaps, should be used to support water resources decision making e.g., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], the introduction of Bayes' Theorem into hydrology marked a major turning point. There is little argument that Bayesian analysis is on the rise in hydrologic circles [4,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]-with the number of publications returned from a Web of Science 'Bayes hydrology' search languishing at fewer than 10 until 2009, then increasing dramatically since (Figure 1).…”