For the dike strengthening project Krachtige IJsseldijken
Krimpenerwaard (KIJK) a study has been undertaken to optimize the amount of
land subsidence. Based on archive information originally a subsidence rate
of 11 mm yr
Since January 2017 the assessment of safety for primary dikes in the
Netherlands should comply to the WBI2017, see MIM (2017). One of the criteria
to be checked is the height of the dike to withstand hydraulic loading
conditions. The level of the dike crest is an important factor, so the
amount of land subsidence must be considered. This paper covers the
determination of land subsidence for the dike strengthening project
Krachtige IJsseldijken Krimpenerwaard (KIJK). The 10 km long KIJK project is
located next to the river Hollandse IJssel, in the Krimpenerwaard near
Rotterdam, the Netherlands, see Fig. 1. The Krimpenerwaard is an area
consisting of soft Holocene soil layers with ongoing subsidence mainly
caused by changing groundwater levels and the associated drying out and
oxidation of peat. The rate of subsidence for the crest of the dike itself
is different from that of the hinterland. Based on information of the Water
authority “Hoogheemraadschap van Schieland en de Krimpenerwaard” (HHSK)
the average rate of subsidence for the crest of the dike is about 11 mm yr
The first step was to plot all the data of each dataset to determine an average subsidence rate along the dike. Also, the “outliers” in the data could visually been recognized and
Location KIJK project; Hollandse IJssel between Krimpen – Gouderak [aerial photo 2016; nationaal georegister].
the locations of these outliers can be determined. Explanations for these
outliers were sought based on different factors such as, the soil profile,
the profile of the Hollandse IJssel underneath the waterline or other
activities, e.g. previous strengthening projects on parts of the dike or
road works. Based on the explanation of the outliers the assumption was made
that a subsidence rate of more than 20 mm yr
The first step of the study was to reanalyse the archive data of HHSK on
which an average subsidence rate of 11 mm yr
Determination of average subsidence rate based on HHSK archive data.
To determine the rate of subsidence for the crest of the dike, monitoring data from INSAR and LiDAR measurement is analysed.
INSAR is a technique that determines deformations of surface points based on
radar satellite measurements. With this technique the deformation from a
point can be measured with high precision, in the order of millimetres. It
must be noted that the precision depends on the weather conditions during
the time of measurement and the resolution of the satellite. For the INSAR
measurements, data from points located on the crest of the dike during the
period between 2013 and 2016 is used. The used satellite data is generated
and processed by SkyGeo and is shown in Fig. 3. From the weighted average it
appears that a reasonably good bandwidth between 5 and 10 mm yr
Determination of average subsidence rate based on INSAR measurements from the period 2013–2016.
Determination of average subsidence rate based on difference in LiDAR data from 2008 and 2014.
Also, the Current Dutch Elevation (Actueel Hoogtebestand Nederland, AHN) is
used for determining the subsidence rate. The AHN map is a digital height
map for the Netherlands based on 3D-height information obtained by LiDAR
measurement from airplanes or helicopters. The map contains detailed and
precise information based on an average of eight measurements per square
meter. AHN has a systematic error of 5 cm and stochastic error of 5 cm
(
Comparison of subsidence rate determined with different measurement methods and HHSK archive data.
These peaks are in the ranges Hm 29.75–30.1 and Hm 32.65–33.05. These
outliers are in good agreement with 2 of the 3 outliers as found in the
measurement data of the INSAR measurements. The average subsidence rate from
the LiDAR data over the entire dike is approximately 9 mm yr
The comparison of weighted average of the subsidence rate from the three
different datasets is shown in Fig. 5. From the graph it can be concluded
that:
Between 25.58 and 27.1 a good agreement is found between all the
datasets. It is noticed that in the LiDAR data outliers are found above 10 mm yr In the INSAR and LiDAR for the trajectory 29.75–30.2 and 32.65–33.0 peaks
are found in the subsidence rate. These peaks are not present in the HHSK
data. This could be explained that by the fact that the INSAR and LiDAR
measurements (respectively 2013–2016 and 2008–2014) are of a later period
than the data from HHSK (1961–2007). Between the trajectory 30.2 and 32.65 the determined subsidence rate for
the three datasets well matches. Excluding the outlier in the INSAR between
approximately 31.4 and 31.7 and an outlier with a very low subsidence rate
in the LiDAR between approximately 32.05 and 32.65. For the trajectory 33.0 to 37.53 the subsidence rate as found from the
INSAR data and from HHSK reasonably match. The data from the LiDAR data
shows generally a higher subsidence rate. In general, the INSAR data and the HHSK data give almost the same average
subsidence rate for the entire dike of about 7 mm yr
In Fig. 6 the determined subsidence rate for the whole trajectory as well
for a specific dike section is shown. For the dike sections N until U the
LiDAR data shows a higher subsidence rata of about 4 mm yr
Comparison of subsidence rate for every dike section as determined with the three different datasets.
Comparison of determined subsidence rate with thickness Holocene soil layers.
Also, a relation was sought between the subsidence rate and the profile of the Hollandse IJssel underneath the waterline as determined with bathymetry (IB-KIJK, 2017). For some locations the bathymetry showed a steeper underwater slope or a local deepening of the bottom. This can indicate a weaker location in the dike with a trigger for outward movement of the dike, which can cause a higher subsidence rate. For some locations along the dike this relation was found, but overall there was not a good explanation of a higher subsidence rate due to the underwater profile of the Hollandse IJssel.
In this paper the INSAR and LiDAR monitoring data and the determination of
the rate of the subsidence for the KIJK dike project are discussed. Based on
the results from this study the rate of subsidence for the crest of the dike
could be reduced from an average of 11 mm yr
A request for the provision of the data, as owned by HHSK, will be treated by HHSK based on the purpose of the request. To determine whether the request can be granted, the purpose must be specified.
MK and RRB made the analysis of the data. JKH, CB gave advice during the analysis. MW was representative of the HHSK for the project. MK prepared the manuscript with contribution from all co-authors.
The authors declare that they have no conflict of interest.
This article is part of the special issue “TISOLS: the Tenth International Symposium On Land Subsidence – living with subsidence”. It is a result of the Tenth International Symposium on Land Subsidence, Delft, the Netherlands, 17–21 May 2021.
The work presented in this paper is part of the KIJK dike strengthening project in the Netherlands. The authors would like to thank their partners from IB-KIJK, BWZ Ingenieurs and Infram and the anonymous reviewers for their comments to improve the quality of the paper.