3.4 Shoreline Compartment
43
to 0.3 in 2020 (DNV GL, Akvaplan-niva and Acona 2020), is used to calculate the
impacted width (W imp ) of the oiled shore in each segment.
Samaras et al. (2014) used tidal range (TR) and beach slope (sl) in order to define
the width of the impacted coastal zone (W imp ) by:
W imp,r =
TR
sin(atansl)
× 0.3
(3.6)
The oil film thickness (T) for each ESI segment is then calculated by:
T r =
V r
L r × W imp,r
(3.7)
where V r is the amount of oil stranded and L r is the length of the shoreline (segment
of ESI ranking). The total impact for each ESI ranking is then given by the total
length (L) for all grid cells where the thickness is above the lethal threshold value
(TH). TH used in ERA Acute is 1 mm for vegetation (herbaceous plants and trees)
on ESI categories 8–10, and 0.1 mm (100 μm) for invertebrate epifauna living in
intertidal habitats on hard substrates (based on a review by French-McCay 2009). In
a recent study, Bock et al. (2018) used 100 μm (lower)/1 mm (upper for vegetation)
and 10 μm (lower)/100 μm (upper) for intertidal invertebrates.
Imp r =
cell
L r |T r ≥ TH
(3.8)
3.4.2 Time Factors and Recovery Modelling
Experience from shoreline oiling after the Deepwater Horizon Oil Spill (DHOS)
also illustrate how erosion and depositional processes of the beach cycle, seasonal
wind pattern and storms to a large extent impact how oil became buried, exposed and
remobilized (Michel et al. 2013). Oil is removed by natural processes (or clean-up)
until the shoreline is eligible for recovery and recolonization of species. The lag phase
(t lag ) of a shoreline after oiling can be defined as the period of oil thickness above
the effect-threshold value. It is influenced by volume, oil type and weathering state,
shoreline hydrodynamic energy level, OHC and intrinsic oil degradation processes.
Due to the more rapid removal of oil from shorelines with high wave energy, a separate
lag-phase in the damage expression is considered to be relevant for medium and low
energy shorelines, while the recovery time for high energy shorelines can be based
on the length of the restoration phase only. A look-up table based on hydrodynamic
energy level in combination with oil type specific impacts is implemented as outlined
in Table 3.2.
43
to 0.3 in 2020 (DNV GL, Akvaplan-niva and Acona 2020), is used to calculate the
impacted width (W imp ) of the oiled shore in each segment.
Samaras et al. (2014) used tidal range (TR) and beach slope (sl) in order to define
the width of the impacted coastal zone (W imp ) by:
W imp,r =
TR
sin(atansl)
× 0.3
(3.6)
The oil film thickness (T) for each ESI segment is then calculated by:
T r =
V r
L r × W imp,r
(3.7)
where V r is the amount of oil stranded and L r is the length of the shoreline (segment
of ESI ranking). The total impact for each ESI ranking is then given by the total
length (L) for all grid cells where the thickness is above the lethal threshold value
(TH). TH used in ERA Acute is 1 mm for vegetation (herbaceous plants and trees)
on ESI categories 8–10, and 0.1 mm (100 μm) for invertebrate epifauna living in
intertidal habitats on hard substrates (based on a review by French-McCay 2009). In
a recent study, Bock et al. (2018) used 100 μm (lower)/1 mm (upper for vegetation)
and 10 μm (lower)/100 μm (upper) for intertidal invertebrates.
Imp r =
cell
L r |T r ≥ TH
(3.8)
3.4.2 Time Factors and Recovery Modelling
Experience from shoreline oiling after the Deepwater Horizon Oil Spill (DHOS)
also illustrate how erosion and depositional processes of the beach cycle, seasonal
wind pattern and storms to a large extent impact how oil became buried, exposed and
remobilized (Michel et al. 2013). Oil is removed by natural processes (or clean-up)
until the shoreline is eligible for recovery and recolonization of species. The lag phase
(t lag ) of a shoreline after oiling can be defined as the period of oil thickness above
the effect-threshold value. It is influenced by volume, oil type and weathering state,
shoreline hydrodynamic energy level, OHC and intrinsic oil degradation processes.
Due to the more rapid removal of oil from shorelines with high wave energy, a separate
lag-phase in the damage expression is considered to be relevant for medium and low
energy shorelines, while the recovery time for high energy shorelines can be based
on the length of the restoration phase only. A look-up table based on hydrodynamic
energy level in combination with oil type specific impacts is implemented as outlined
in Table 3.2.