34
3 An ERA Acute Model Overview
A rate-duration matrix including the probability distribution between rate (groups)
and duration intervals can have different forms and detail, depending on the
input given. A fictive, simplified example from a multi-scenario blowout-DSHA
is presented in Table 3.1 and the frequency distribution is illustrated in Fig. 3.1. As
a simplified alternative to the multi-scenario assessment, the DSHA could alternatively be a single scenario oil spill modelling restricted to one (weighted) oil spill
rate and duration (100% rate probability). The DSHA frequency of a blowout from
the example exploration drilling is 1.2 × 10
−4 .
Each combination of rate and duration is run as a set of many simulations in oil
spill trajectory modelling, given as inputs to ERA Acute for calculating exposure. The
oil spill model results file must list results of each single simulation in the scenario,
and must contain the following information for each grid cell:
• Sea surface: Oil film thickness, oil coverage and duration of exposure.
• Shoreline: stranded oil amounts.
• Water column: Concentration of total hydrocarbon content (THC max ) in the water
column or potential mortality % if available from the oil drift model (see 3.6.1).
• Seafloor: Oil amounts on the seafloor.
Oil spill trajectory data are exported to the same grid as used for the VEC data and
the connection between the two data types is the cell ID. VEC data and the additional
input data needed for the exposure calculations are described for each compartment
in the sections below.
3.2 Impact and Restoration Modelling
Calculations of damage are carried out in two main steps comprised of several substeps (Fig. 3.2). Step (A) calculates the magnitude/extent of the impact and Step B
calculates the duration of the impact. Three time-factors are calculated from impact to
recovery of the impacted VEC (see Fig. 3.2). The basic framework of the calculations
is common between the compartments, including many of the general summaries of
risks across cells, simulations and scenarios. However, compartments and/or VECs
can be impacted and restored through different mechanisms of action and regrowth,
as described in the compartment development reports (Bjørgesæter and Damsgaard
Jensen 2015; Brude et al. 2015; Brönner and Nordtug 2015; Brönner et al. 2015,
2017; Stephansen et al. 2015, 2017a, b). Calculations of lethality and recovery time
factors are therefore different between compartments. The common framework is
described in this section.
3.2.1 Step A: Impact Modelling
All compartments build on the same general methodology framework for the basic
impact calculation for a cell and simulation at step A; incorporating probability of
3 An ERA Acute Model Overview
A rate-duration matrix including the probability distribution between rate (groups)
and duration intervals can have different forms and detail, depending on the
input given. A fictive, simplified example from a multi-scenario blowout-DSHA
is presented in Table 3.1 and the frequency distribution is illustrated in Fig. 3.1. As
a simplified alternative to the multi-scenario assessment, the DSHA could alternatively be a single scenario oil spill modelling restricted to one (weighted) oil spill
rate and duration (100% rate probability). The DSHA frequency of a blowout from
the example exploration drilling is 1.2 × 10
−4 .
Each combination of rate and duration is run as a set of many simulations in oil
spill trajectory modelling, given as inputs to ERA Acute for calculating exposure. The
oil spill model results file must list results of each single simulation in the scenario,
and must contain the following information for each grid cell:
• Sea surface: Oil film thickness, oil coverage and duration of exposure.
• Shoreline: stranded oil amounts.
• Water column: Concentration of total hydrocarbon content (THC max ) in the water
column or potential mortality % if available from the oil drift model (see 3.6.1).
• Seafloor: Oil amounts on the seafloor.
Oil spill trajectory data are exported to the same grid as used for the VEC data and
the connection between the two data types is the cell ID. VEC data and the additional
input data needed for the exposure calculations are described for each compartment
in the sections below.
3.2 Impact and Restoration Modelling
Calculations of damage are carried out in two main steps comprised of several substeps (Fig. 3.2). Step (A) calculates the magnitude/extent of the impact and Step B
calculates the duration of the impact. Three time-factors are calculated from impact to
recovery of the impacted VEC (see Fig. 3.2). The basic framework of the calculations
is common between the compartments, including many of the general summaries of
risks across cells, simulations and scenarios. However, compartments and/or VECs
can be impacted and restored through different mechanisms of action and regrowth,
as described in the compartment development reports (Bjørgesæter and Damsgaard
Jensen 2015; Brude et al. 2015; Brönner and Nordtug 2015; Brönner et al. 2015,
2017; Stephansen et al. 2015, 2017a, b). Calculations of lethality and recovery time
factors are therefore different between compartments. The common framework is
described in this section.
3.2.1 Step A: Impact Modelling
All compartments build on the same general methodology framework for the basic
impact calculation for a cell and simulation at step A; incorporating probability of