Dynamic Dunes 2015 – 7 October 2015

Workshop Creating blowouts: what to expect?

Examples and lessons from the PWN dunes

Tycho Hoogstrate & Dick Groenendijk

Dunes at Heemskerk; 1952 en 2008

Nitrogen deposition; declining grazing populations; grass and scrub encroachment.

Less open sand and mosaic with scrub and dune grassland is more homogeneous.

A few PWN-statistics…….2003; North Holland Dune Reserve (5200 ha); counting visible blowouts on aerial photos.

Circa 80% of the blowouts within thefirst 1000 meters from the beach.

Circa 60% of the blowouts 10-100 m2

Not only small scale blowouts

Reactivating rather large blowout at Heemskerk (+25% compared with blowout from 1952 foto).

Size of blowout depends on the local situation (like distance from thesea, geomorphological characters, presence/absence of other blowouts, etcetera) as well as the goal of the project (reset of a grassland system or small scale restauration of mosaic in grasslands).

Does size matter?

Last parts of dynamic blowouts at lime rich dunes at Castricum;

Valuable refugia of insects and plant species > be careful withrejuvenation of these type of blowouts.

Small blowout near Castricum (5 km inland);

Still active partly due to recreation. More blow outs? Rejuvenation? Better to handle scrub to prevent overgrowinginstead of managing the blowout itself.

Natural blowout near Bergen in lime poor dunes.

Erosion ridges

Erosion ridges found on many natural blowouts (near Egmond)

• Erosion ridges very important > home for manyinsects

• Most erosion down the plant roots

• Plant material dying

• ‘Balcony structure’ > keeping dry sand > erosive

Artificial erosion ridges can be created easily.

Circa 20-30 cm high.

Southern slope of a large-sized blowout.

Creating erosion ridges

A few weeks after completion

• ‘Balcony structure’

• Note the absence of ridges in the background

• Sand can escape out of the project to provide dunegrasslands with a dusting of lime rich sand

No erosion ridges on northern and western slope; slope very gentle

Eastern slope withsteeper slope

Overview of the project after one year

Total area circa 1000 m2

Erosion ridges at southern slope

Large deposition zone

Art in the PWN-dunes………………

Sculpture garden

How to create small scale blowouts?

Just place art in the dunes!

Discussion topicsIs small scale eolean activity a cure for deteriorated Grey dunes?

Do we understand the process of small scale eolean activity enough to make them?

When are blowouts successful?

Stabilization of blowouts: failure or success?

In which dune zones to create blowouts?

Which size and density of blowouts?

Which time scale for ‘planning’ blowouts?

How to create blowouts?

What are the clues to create successful blowouts?