Content uploaded by Maarten F. de Jong
Author content
All content in this area was uploaded by Maarten F. de Jong on Nov 11, 2016
Content may be subject to copyright.
The ecological effects of
deep sand extraction and
implications for the future
Maarten de Jong
De Jong EcoLogical consultancy
Wageningen Marine Research
Building with Nature
North Sea Open science Conference 2016, Oostende, Belgium
PhD research
•First only shallow extraction(-2 m), recently up to –20 m
but ecological effects unknown.
•Since 1974 increasing demand for marine sand in the
Netherlands.
•We studied effects on macrozoobenthos, demersal fish and
abiotics.
•We developed optimisation design rules for extraction
sites in areas without sandbanks.
Activities on the BCS
•Sand extraction
•Sediment dump
•Shipping
•Cables and pipes
•Wind energy
•Fisheries
Sand extraction on the BCS
•Past: avg. y-1: 1.5 Mm3, mainly from zone 2
•Pipeline: 1991 and 1997, 0.7 and 2.5 Mm3
•Recent: 3-5.5 Mm3, 20 Mm³ for 10 y. (nourishments)
Sand extraction on the BCS
•From the crests of sandbanks
•Zone 2, KB, BR + OD
•Zone 1, Thornton B.
•Zone 4, Hinder B.
•- 5 m below seabed
•Zone 3, Sierra Ventana
Sediment dump but now
used for extraction
(cement mortar)
Dredging with Nature
•Dredging at the crests of sandbanks, expected recovery due to
the high-dynamic behaviour (van Lancker et. al 2010).
•Development of depressions, with no signs of morph.
Recovery.
•Max. extraction depth of -5 m, not evenly distr. (Degrendele et
al, 2016).
Short-term developments (BCS)
•Plans to redefine the reference level of sand extraction,
> -5 m, vulnerable areas, sediment comp., sandbank morph.
and geology (MSFD).
•4D resource decision support system: 3D geological
models + numerical environmental impact models (Lancker et
al. 2017).
Sand extraction on DCS (PhD)
4 “Case studies” on DCS:
1
1. 2 m ex. Depth
2
2
2. 8 m deepened shipping lane
3
3
3. MV2 pit (20-24 m ex. depth)
MV2 (2), a large harbour
extension of the PoR: 220 Mm3
4
4. Ecological landscaping
Outside 20 m depth contour,
dashed patches.
Seabed enrichment MV2
•Natural seabed patterns harbor Δ ecological zones
•2 sand banks were dredged
Natural sandwavesParallel sandbank
Oblique sandbank
Ecological effects sand extraction
•Shallow extraction recovery 2-4 y (van Dalfsen et al. 2000)
•Deep extraction changes in species comp. white furrow
shell (
Abra alba
) and plaice (
Platessa platessa
) and 10-20
times > biomass (de Jong et al. 2014, 2015)
•and > fine sediment + > sedimentation rate + recovery to
original state decades –century
•Ecological landscaping changes in ecology
Ecosystem-based design (EBD) rules
Ecosystem-based design (EBD) rules
Ecology + bed shear stress ( 𝜏𝑏2D)
Force per seabed surface area exerted by flowing water
𝜏𝑏2D =𝜌𝑠𝑒𝑎𝑤𝑎𝑡𝑒𝑟∗ 𝑔 ∗ 𝑼𝟐
𝐶2
2 m extr. depth
Ecosystem-based design (EBD) rules
Conclusions
(Large-scale) Deep sand extraction:
•Significant effects on (a)biotics, < surface area, CO2, costs and
more efficient use of sand resources
Optimization rules:
•Ecological conditions of Dutch case-studies can be realised for
other areas with Δ depth and peak flow velocity (de Jong et al.
2015).
Sand extraction strategy
•The rules can be used to balance sand yield and ecological
effects (de Jong et al. 2016).
Ecosystem-based design rules for BCP
Elongated sandpits and in line w.r.t. tidal current → flow
contraction → > bed shear stress, erosion, coarser sediment → Δ
ecology
Ecosystem-based design rules
for current increasing pits can be
developed
Recommendations for BCP
Determine maximum allowable difference in bed shear stress.
Extraction of north-western or
south-eastern parts instead
of middle parts.
Use 3D hydrodynamic models to asses pit
designs on beforehand.