Increasing biodiversity on flora-rich embankments

Related theme: Biodiversity

Challenge - Mowing-management regime

Waterschap Hollandse Delta (water board) manages embankments whose primary function is as flood defence. And so the grass cover needs to be mown to prevent the soil suffocating and compromising the stability of the dyke. But frequent mowing negatively impacts the flora and fauna. Therefore, Waterschap Hollandse Delta asked TAUW to examine which embankments and verges were most suitable for high species richness and how the mowing frequency could be adjusted to maximise the biodiversity on the embankments and verges. The dykes needed to be assessed on their environmental potential. Factors such as sun exposure, gradient of the embankment, use of pesticides in the vicinity were just some of the aspects to be considered. 

Solution - An integral approach

TAUW set up a team of professionals: colleagues from biodiversity, soil and groundwater and GIS came together to map the area, conduct field studies and take soil samples. The team analysed the soil on phosphates, acidity and loam levels and then drew up a weighting matrix to determine which sites were most suitable. On that basis TAUW was able create a map showing which sections had most ecological potential.

In addition to showing which embankments scored highest on potential, TAUW also came up with a grassland management regime, which includes the type of mowing machinery that should be used, the frequency and phasing, the height of the cut and if and when to remove the cuttings.  The project is being monitored in the long term, particularly on biodiversity and erosion resistance.

The result is a comprehensive advice report with which Waterschap Hollandse Delta was able to develop a management and monitoring plan to optimise vegetation and biodiversity on the embankments  

Impact - Working against floods and for flora and fauna

Under the new mowing regime, these grass-covered embankments have the potential to become ecological havens for plants and insects and thereby strengthen the biodiversity of flora and fauna living on them. They also act as connectors of natural areas and so their impact extends beyond this site. 

Partnership - Solid research, practical results

“We maintain over 800 kilometres of dike. With the current biodiversity crisis, the water authority wants to increase the diversity of vegetation on these dikes. As a starting point, we wanted to know where the high potential places were located. TAUW helped us to find the location with the highest potential. Based on the results of their research, we changed the mowing maintenance to phased mowing on 5 locations with high potential. We are very satisfied with the great work TAUW did to help us invest in the places with the biggest opportunities and develop a diverse vegetation." - Laurens van Zee, Hollandse Delta