Project 1 - Analyses of Shoreface nourishment


 20.2.19

The purpose of project 1 is to gain more knowledge about the effect of shoreface nourishment as coastal protection.

Therefore shoreface nourishments at Krogen and at Skodbjerge will be analyzed in the software MorphAn, developed by Deltares for Rijkswaterstaat.

In the larger context the result of the analysis from Denmark will be compared with the results of the same analysis made by the other partners in the Building with Nature project.

I December 2019 the first product in project 1 finished with a report "Shoreface nourishment effects – An analysis of the 2011 nourishment performed at Skodbjerge".

The area af Skodbjerge
The area af Skodbjerge

One of seven national reports

The Danish report is one of seven national reports presenting the results from each individual living laboratory. The Danish living laboratory Skodbjerge is located on the Danish North Sea Coast. The results will be compiled into a joint co-analysis providing for comparing nourishment performance and generating a better understanding of the factors that determine nourishment evolution. The Skodbjerge analysis focus on the nourishment performed in 2011, but the effects of other nourishments, especially the one performed in 2010 at Skodbjerge have to be taken into account because of the temporal scale of nourishment effects.

The Skodbjerge analysis aimes to answer the following questions regarding to the nourishment:

  • What was the lifetime of the 2011 shoreface nourishment?
  • How did the 2011 nourishment redistribute along and cross-shore?
  • How did the 2011 shoreface nourishment influence the dry part of the coastal profile, especially the safety level?
  • How is the nourishment decay correlated with the hydrodynamic forcing?

The living laboratory Skodbjerge is located on the Danish North Sea Coast, where the Danish Coastal Authority is executive in performing coastal protection.

The Danish North Sea Coast is a micro tidal wave dominated sandy coast. The coast is highly dynamic and the morphology changes responding and adjusting to the predominating climate conditions. Large alongshore variations in the coastline have been documented and indentations, which migrate as the bar system migrates alongshore in the sediment transport direction, which is southbound. These coastline indentations, which are characterized by a narrowing of the beach, mark potential erosional hotspot. The number of bars, their size and position in the offshore direction change rapidly, especially during storms.

A graphic overview over dates when profile measurements and LiDAR scans were performed, within the period after the recent shoreface nourishments iis illustrated in the figure below.

Figure 2: Timeline of the shoreface nourishment, LiDAR scans and serveys of West coast profiles and local profiles
Figure 2: Timeline of the shoreface nourishment, LiDAR scans and serveys of West coast profiles and local profiles

The analysis is performed using coastal state indicators

The analysis of quantitative morphological development is performed using coastal state indicators (CSI's). CSI's are commonly agreed definitions of features that provide information on the state of a coast at a certain moment in time. The use of CSI's will align the national analyses carried out by each member in WP3 of the Building with Nature project, and will allow them to be joined into one co-analysis.

A CSI is a feature; morphological zone or height level which can be determined using cross-shore transects. When monitored over time, a CSI shows the development of the morphological system and reveals changes in evolutionary trends.The monitored development depends on the type CSI e.g. Changes in sand volume in a zone, the width of a coastal zone, the cross-shore position of a morphological system and reveals changes in evolutionary trends. In table 4 the applied coastal terminology, the CSI's and their interrelation is described.  See table 4 here under Filer

In figure 3 the general terminology used to describe the coastal profile is illustrated. On the vertical axis various levels in the profile are shown. The horizontal axis shows different morphological zones in the profile. See figure 3 under Filer.

The results of the studies using the common methodology are presented and described in several figures with graphs. An example can be seen in figure 4 under Filer.

The conclusions

The conclusions of the analysis at Skodbjerge are that one of the benefits of nourishments as a means of coastal protection is the fact that they blend into the natural environment. In turn, this means that the effects are difficult to untangle from the natural variation of the coastal system. This analysis has attempted to identify the effects of shoreface nourishment by taking the autonomous behavior of the system into account. This has proven important since in depth knowledge of the system is required in order to put the nourishment effects into perspective and thereby reveal which effects are of such a magnitude that they cannot be ascribed to the natural variations and vice versa.

In this study, the evolution of the 2011 nourishment has been investigated in depth. In order to do this, the nourishment in 2010 has been taken into account to determine if the observed evolution was influenced by this prior nourishment. Furthermore, the 2010 nourishment functions as a basis for comparison and evaluation of the 2011 nourishment design.

See the complete national anlaysis Shoreface nourishment under Filer.

In the overall Building with Nature project the other partners in workpackes 3 have also made a national analysis of one or more of their shoreface nourishment. All of these results will be incorporated in a co-analysis. This co-analysis will be completed during 2019.

Project 1 will run in the period 2017-2019.