The geomorphological response of Dutch inland drift sands to changing wind regimes
|Location||International Geological Congress,oslo 2008|
|Author||Jungerius, Pieter Dirk; Riksen, Michel; van den Ancker , Johanna|
|Holding Date||08 September 2008|
Active drift sands once covered 8.500 to 13.000 km2 of the ’European sand belt’ which extends from UK eastward across Belgium, The Netherlands and Germany to Poland and beyond. Now, less than 1 % of this eolian landscape remains, almost exclusively in The Netherlands. The other 99 % is stabilized, at first by planting trees, later spontaneous by vegetation that is stimulated by atmospheric N deposition. The remaining drift-sand landscapes are now protected as EU Habitat type. The Dutch national government subsidizes geomorphological research because the sustainable management and restoration of former drift-sand areas require insight in the geomorphological structure and functioning of drift sands.
Recent laser altimetry images reveal that drift sand areas have a characteristic internal structure which shows that winds from the SW were the dominant factor: a deflation zone with coppice dunes at the SW edge merges leeward into a transport plain which in turn passes into an accumulation zone with parabolic dunes at the NE edge. This dominance of SW winds is not surprising because it is the general trend of all Weichselian and Holocene eolian deposits in this region. It was brought to an end when trees were planted at the SW side of the drift sand areas. From then on the NE winds shared the role of the SW winds as transporting agent, building up new dunes against any obstacle in its way. This changes the geomorphological structure of the drift sands. Although far less frequent than SW winds, NE winds are more efficient because they are less gusty and blow in drier periods.
To measure the consequences of this change, wind speed and direction data and other meteorological parameters were collected and correlated with sediment fluxes in an experimental setup on Kootwijkerzand, one of the largest active drift-sand areas of the Netherlands. The measurements showed that winds from NE direction are now responsible for 40% of the registered saltation activity against 60% by SW winds. Other eolian landscapes such as the coastal dunes where the formation of blowouts is important, react in a comparable way to changing wind regimes.
With the insights issuing from these studies it is possible to assess the geomorphological effects of potential changes in wind direction triggered by future climate change.