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How to seize opportunities and avoid risks of sand extraction

Authors:
  • Ministerie van Landbouw natuur en voedselkwaliteit

Abstract and Figures

For Maasvlakte 2 (MV2), a seaward harbour extension of the Port of Rotterdam, 220 million m3 of sand was extracted in a 15 km2 large area with water depths of 20 m and sand extraction depths up to 20 m. We studied the ecological effects and compared these with other sand extraction case-studies with intermediate and shallow extraction depths on the Dutch continental shelf (DCS). We observed significant short-term changes in faunal species composition and sediment characteristics in the 40 m deep MV2 borrow pit. Biomass of macrozoobenthos and demersal fish biomass increased on average 10 to 20-fold in the deep areas 2 years after extraction. Macrozoobenthos and demersal fish distribution correlated with sediment and hydrographic characteristics and time after cessation of sand extraction. Ecological and bed shear stress data were combined and transformed into Ecosystem-based design (EBD) rules which can be used in the design phases of future borrow pits in order to simultaneously maximize the sand yield and decrease the surface area of direct impact. The EBD rules can be applicable in other regions than the DCS depending on the extraction depth, hydrodynamic regime, and the supply of suspended matter. For areas outside Europe, ecological data for comparable deep sand extraction sites may be necessary. In general, the EBD rules can help to even make large-scale and deep sand extraction sustainable by mitigating or preventing related processes with potential negative impacts. Keywords: deep sand extraction, macrozoobenthos, hydrodynamics, ecosystem http://www.ices.dk/news-and-events/asc/ASC2016/Pages/ThemeSessionDetail.aspx?ThemeSession=K
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How to seize opportunities
and avoid risks of sand
extraction
Maarten de Jong (BwN)
Bas Borsje (Deltares, TU Twente)
Martin Baptist (Wageningen Marine Research)
Daan Rijks (Boskalis)
Sand extraction in Europe
European seabed substrate
Coastal migration in Europe
Sand extraction DCS
Future: Nourishments w.r.t. sea level rise 4085 Mm3 y-1?
0
20
40
60
80
100
120
140
Volume sand (Mm3)
Past: avg. y-1: 26 Mm3, nourishments: 12 Mm3
Recent: MV2: 220 Mm3 + Sandmotor: 21.5 Mm3
Sand extraction on DCS and PhD research
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.
Enrichment of MV2 seabed
Natural seabed patterns (sand waves) have Δ ecological zones
In MV2, 2 sand bars were dredged
(parallel and oblique)
Methods of research (2009-2012)
Macrobenthos and sediment
(Box core)
Macrobenthos on the seabed
(bottom dredge)
Fish (Beam trawl)
Multibeam images
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 ( 𝜏𝑏 2D)
Force per seabed surface area exerted by flowing water
𝜏𝑏 2D = 𝜌𝑠𝑒𝑎𝑤𝑎𝑡𝑒𝑟 ∗ 𝑔 ∗ 𝑼𝟐
𝐶2
2 m extr. depth
Ecosystem-based design (EBD) rules
Applicability EBD rules
> extr. depth > fine sediment >
Abra alba
and plaice also > NS
Conclusions
𝝉𝒃 2D is a useful steering parameter and ecological output can
be designed via extraction depth.
𝝉𝒃 2D contains:
More information than dredging intensity
Extraction depth
In the case of deep extraction more relevance than D50
With EBD rules, ecological conditions of excising sand
extraction case studies can be realized in regions with Δ water
depth and peak flow velocities (de Jong et al. 2015).
Recommendations
Study impact of intermediate ex. depths benthos,
fish, sediment
Study medium and long-term impact of deep extraction
including sedimentation rate and oxygen content
Validate applicability of EBD-rules on DCS and beyond.
Data sources
Emodnet: Bathymetry
Emodnet: Human pressures such as aggregate extraction
Emodnet: Biology: occurrence of species (EurOBIS: The
European Ocean Biogeographic Information System)
Port of Rotterdam, van Oord, Boskalis, RWS
Maarten de Jong | Marine Ecologist
+31 6 44598167 | mfdejong@hotmail.com
mfdejong4.wixsite.com/de-jong-consultancy
De Jong
EcoLogical Consultancy
Questions
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