B. Strijker
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8 records found
1
The role of load variations in assessing credible dike failure probabilities
Balancing load and strength uncertainties
Assessing dike safety is of key interest to societies in low-lying areas, but results can be implausible when, for example, they contradict the observed performance of the dike. To improve credibility, load monitoring data can be incorporated using reliability updating techniques. This paper investigated the role of load variations in reliability updating and assessing credible failure probabilities. It was found that the impact of reliability updating increases when load variations are small, as a large contribution to failure probabilities comes from relatively frequent load levels, of which the conditional failure probabilities are reduced most through reliability updating. Moreover, a credibility check was introduced for dikes that have been stable for decades, where load levels with return periods of up to 10 years are not expected to contribute more than 50% to the failure probability, indicating an imbalance between load variation and strength uncertainty. This imbalance occurs when the inverse gradient of the fragility curve exceeds 1.5 times the decimate height of the load. Many Dutch dikes, including canal dikes and dikes along the large lakes and delta regions, have small decimate heights. For these dikes, strength uncertainties must be sufficiently small to obtain credible failure probability estimates.
Geohydrology and safety of Dutch canal dikes: threats from above
From monitoring to probabilistic risk assessments
The detailed monitoring series included two extremely dry summers (2020 and 2022). Hydraulic heads at inner-slope and toe monitoring points showed strong seasonal variation. During winter, conditions were near saturation, while during dry summers heads dropped down to nearly 2 m, despite outside water levels remaining nearly constant. Non-hydrostatic hydraulic head levels were observed within dike bodies, conditions often not accounted for in safety assessments for drought situations. The precipitation deficit proved the most reliable meteorological drought indicator, outperforming the standardised drought indicators (SPEI and SPI).
Analysing the nationwide dataset with time-series models, a non-linear model performed best, resulting in 35 reliable time-series models. Four clusters of dikes were identified, differentiated by response times, defined as the time required for 95% of an impulse's influence to dissipate. Longer response times cause peak heads to occur later in the winter. Peak head statistics indicated a that extreme heads are close to yearly occuring heads, with a median decimate height of 15 cm and a range of 5 to 50 cm. By 2100, extreme peak heads are expected to occur between three times less frequently and eight times more frequently, depending on the climate scenario and the type of canal dike.
The time-series models were used to hindcast 60 years of hydraulic head levels and estimate spatial dependencies, quantified using the length-effect factor of peak heads. At the polder scale, variation in head responses can increase the factor by a factor of four to five, whereas spatial weather variability can double it. At the scale of the entire canal-dike system, the length-effect of peak heads is dominated by spatial weather variability, increasing from about 6 for annually occurring heads to around 40 for heads with an exceedance frequency of 1/100 per year.
The impact of small load variations on reliability updating was analysed. The impact of reliability updating increases as load variations decrease, regardless of the prior failure probability. The two canal dikes, with decimate heights below 10 cm, benefited most from reliability updating, whereas updated failure probabilities of the river dikes changed only slightly. A credibility check was introduced: when uncertainty in dike strength is more than 1.5 times larger than the variation in loads, estimated failure probabilities are not credible. Reducing uncertainties in dike strength, through monitoring with reliability updating or more detailed soil strength data, leads to more credible failure probability estimates. ...
The detailed monitoring series included two extremely dry summers (2020 and 2022). Hydraulic heads at inner-slope and toe monitoring points showed strong seasonal variation. During winter, conditions were near saturation, while during dry summers heads dropped down to nearly 2 m, despite outside water levels remaining nearly constant. Non-hydrostatic hydraulic head levels were observed within dike bodies, conditions often not accounted for in safety assessments for drought situations. The precipitation deficit proved the most reliable meteorological drought indicator, outperforming the standardised drought indicators (SPEI and SPI).
Analysing the nationwide dataset with time-series models, a non-linear model performed best, resulting in 35 reliable time-series models. Four clusters of dikes were identified, differentiated by response times, defined as the time required for 95% of an impulse's influence to dissipate. Longer response times cause peak heads to occur later in the winter. Peak head statistics indicated a that extreme heads are close to yearly occuring heads, with a median decimate height of 15 cm and a range of 5 to 50 cm. By 2100, extreme peak heads are expected to occur between three times less frequently and eight times more frequently, depending on the climate scenario and the type of canal dike.
The time-series models were used to hindcast 60 years of hydraulic head levels and estimate spatial dependencies, quantified using the length-effect factor of peak heads. At the polder scale, variation in head responses can increase the factor by a factor of four to five, whereas spatial weather variability can double it. At the scale of the entire canal-dike system, the length-effect of peak heads is dominated by spatial weather variability, increasing from about 6 for annually occurring heads to around 40 for heads with an exceedance frequency of 1/100 per year.
The impact of small load variations on reliability updating was analysed. The impact of reliability updating increases as load variations decrease, regardless of the prior failure probability. The two canal dikes, with decimate heights below 10 cm, benefited most from reliability updating, whereas updated failure probabilities of the river dikes changed only slightly. A credibility check was introduced: when uncertainty in dike strength is more than 1.5 times larger than the variation in loads, estimated failure probabilities are not credible. Reducing uncertainties in dike strength, through monitoring with reliability updating or more detailed soil strength data, leads to more credible failure probability estimates.
Exploring Subsurface Water Conditions in Dutch Canal Dikes During Drought Periods
Insights From Multiyear Monitoring
Hoogwater 2021
Feiten en Duiding
Contributors (in alphabetical order):
Nathalie Asselman (Deltares), Hermjan Barneveld (HKV / Wageningen UR), Jules Beersma (KNMI), Eline Boelee (Deltares), Wouter Botzen (VU Amsterdam), Eefke Copper (TU Delft), Dim Coumou (KNMI), Karin de Bruijn (Deltares), Anniek de Jong (Deltares), Jurjen de Jong (Deltares), Hans de Moel (VU Amsterdam), Ferdinand Diermanse (Deltares), Astrid Fischer (Evides) , Gert-Jan Geerling (Deltares), Marie-Louise Geurts (WML), Rob Groenland (KNMI), Mark Hegnauer (Deltares), Bas Jonkman (TU Delft), Nicole Jungermann (KNMI), Frans Klijn (Deltares), Andre Koelewijn (Deltares), Matthijs Kok (HKV / TU Delft), Elco Koks (VU Amsterdam), Bas Kolen (HKV / TU Delft), Marion Koopmans (Erasmus MC), Laurens Leunge (Deltares), Hans Middelkoop (Utrecht University), Roelof Moll (TU Delft), Jaap Mos (Dunea), Sjoukje Philip (KNMI), Gerbert Pleijter (HKV), Joost Pol (HKV / TU Delft), Stephan Rikkert (TU Delft), Guus Rongen (TU Delft), Rinus Scheele (KNMI), Julius Schlumberger (TU Delft), Peter Siegmund (KNMI), Kymo Slager (Deltares), Frederiek Sperna Weiland (Deltares), Bart Strijker (HKV / TU Delft), Henk v.d. Brink (KNMI), Janko van Beek (Erasmus MC), Marion van den Bulk (TU Delft), Bart van den Hurk (Deltares), Tim van Emmerik (Wageningen UR), Kees van Ginkel (VU Amsterdam / Deltares), Mick van Haren (TU Delft), Margreet van Marle (Deltares), Malou van Schaijk (TU Delft), Dennis Wagenaar (Nanyang TU), Davide Wüthrich (TU Delft) ...
Contributors (in alphabetical order):
Nathalie Asselman (Deltares), Hermjan Barneveld (HKV / Wageningen UR), Jules Beersma (KNMI), Eline Boelee (Deltares), Wouter Botzen (VU Amsterdam), Eefke Copper (TU Delft), Dim Coumou (KNMI), Karin de Bruijn (Deltares), Anniek de Jong (Deltares), Jurjen de Jong (Deltares), Hans de Moel (VU Amsterdam), Ferdinand Diermanse (Deltares), Astrid Fischer (Evides) , Gert-Jan Geerling (Deltares), Marie-Louise Geurts (WML), Rob Groenland (KNMI), Mark Hegnauer (Deltares), Bas Jonkman (TU Delft), Nicole Jungermann (KNMI), Frans Klijn (Deltares), Andre Koelewijn (Deltares), Matthijs Kok (HKV / TU Delft), Elco Koks (VU Amsterdam), Bas Kolen (HKV / TU Delft), Marion Koopmans (Erasmus MC), Laurens Leunge (Deltares), Hans Middelkoop (Utrecht University), Roelof Moll (TU Delft), Jaap Mos (Dunea), Sjoukje Philip (KNMI), Gerbert Pleijter (HKV), Joost Pol (HKV / TU Delft), Stephan Rikkert (TU Delft), Guus Rongen (TU Delft), Rinus Scheele (KNMI), Julius Schlumberger (TU Delft), Peter Siegmund (KNMI), Kymo Slager (Deltares), Frederiek Sperna Weiland (Deltares), Bart Strijker (HKV / TU Delft), Henk v.d. Brink (KNMI), Janko van Beek (Erasmus MC), Marion van den Bulk (TU Delft), Bart van den Hurk (Deltares), Tim van Emmerik (Wageningen UR), Kees van Ginkel (VU Amsterdam / Deltares), Mick van Haren (TU Delft), Margreet van Marle (Deltares), Malou van Schaijk (TU Delft), Dennis Wagenaar (Nanyang TU), Davide Wüthrich (TU Delft)