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10.1 Introduction
The decision to apply chemical dispersants on surface oil is a trade-off between
surface effects (impact of floating and stranded oil) and subsurface effects (direct
impact of suspended oil and potential for sedimentation and sinking). Making an
informed decision regarding such response requires insight into the induced changes
in fate and adverse effects of the oil.
Natural dispersion calculations in the currently available oil fate and transport
models are based on the empirical results of Delvigne and Sweeney, although it is
generally agreed these can be improved (Delvigne and Sweeney 1988; Reed et al.
1999; National Research Council of the National Academies 2005). Furthermore,
these calculations do not permit prediction of chemical dispersion. The calculation
of chemical dispersion in the current oil fate and transport models requires knowledge of the estimated effectiveness of dispersant application rather than providing
output thereof (National Research Council of the National Academies 2005).
Estimating dispersant effectiveness in advance of commencing such oil spill
response relies heavily on expert judgment.
A small group of researchers under the C-IMAGE project (as part of the Gulf of
Mexico Research Initiative) set out to create insight into the processes governing
natural and chemical dispersion of spilled surface oil and to provide a strategy to
assess and predict the added value of chemical dispersion for specific spill conditions and oil qualities. The tiered experimental design allowed for structured analysis of available laboratory results and the identification of unknown parameters
(Zeinstra-Helfrich et al. 2015b). Additionally, the process of entrainment, or initial
submergence of the oil, can be examined more thoroughly in a laboratory environment to quantitatively capture the influence of layer thickness and oil properties on
vertical oil droplet size distribution (Zeinstra-Helfrich et al. 2015a, 2016).
Ultimately, a model was proposed that calculates the evolution of the surface oil
slick as a result of the dispersion process (Zeinstra-Helfrich et al. 2017).
This chapter examines the oil slick elongation model (Sect. 10.2) in order to
explain the influence of different key parameters on dispersion and oil slick (dis)
appearance (Sect. 10.3) and the implications of the results for future decisionmaking (Sect. 10.4).
10.2 How Natural or Chemical Dispersion Affects Oil
Slick Fate
Dispersion is not a singular event but rather a combination of several processes
(Fig. 10.1). Breaking waves temporarily submerge oil through entrainment. The
entrained oil is broken up into droplets, and their size distribution in the water column is dependent on mixing energy, oil properties, and slick thickness. As most oil
is still lighter than water, the droplets rise back to the surface at a rate dependent on
M. Zeinstra-Helfrich and A. J. Murk
10.1 Introduction
The decision to apply chemical dispersants on surface oil is a trade-off between
surface effects (impact of floating and stranded oil) and subsurface effects (direct
impact of suspended oil and potential for sedimentation and sinking). Making an
informed decision regarding such response requires insight into the induced changes
in fate and adverse effects of the oil.
Natural dispersion calculations in the currently available oil fate and transport
models are based on the empirical results of Delvigne and Sweeney, although it is
generally agreed these can be improved (Delvigne and Sweeney 1988; Reed et al.
1999; National Research Council of the National Academies 2005). Furthermore,
these calculations do not permit prediction of chemical dispersion. The calculation
of chemical dispersion in the current oil fate and transport models requires knowledge of the estimated effectiveness of dispersant application rather than providing
output thereof (National Research Council of the National Academies 2005).
Estimating dispersant effectiveness in advance of commencing such oil spill
response relies heavily on expert judgment.
A small group of researchers under the C-IMAGE project (as part of the Gulf of
Mexico Research Initiative) set out to create insight into the processes governing
natural and chemical dispersion of spilled surface oil and to provide a strategy to
assess and predict the added value of chemical dispersion for specific spill conditions and oil qualities. The tiered experimental design allowed for structured analysis of available laboratory results and the identification of unknown parameters
(Zeinstra-Helfrich et al. 2015b). Additionally, the process of entrainment, or initial
submergence of the oil, can be examined more thoroughly in a laboratory environment to quantitatively capture the influence of layer thickness and oil properties on
vertical oil droplet size distribution (Zeinstra-Helfrich et al. 2015a, 2016).
Ultimately, a model was proposed that calculates the evolution of the surface oil
slick as a result of the dispersion process (Zeinstra-Helfrich et al. 2017).
This chapter examines the oil slick elongation model (Sect. 10.2) in order to
explain the influence of different key parameters on dispersion and oil slick (dis)
appearance (Sect. 10.3) and the implications of the results for future decisionmaking (Sect. 10.4).
10.2 How Natural or Chemical Dispersion Affects Oil
Slick Fate
Dispersion is not a singular event but rather a combination of several processes
(Fig. 10.1). Breaking waves temporarily submerge oil through entrainment. The
entrained oil is broken up into droplets, and their size distribution in the water column is dependent on mixing energy, oil properties, and slick thickness. As most oil
is still lighter than water, the droplets rise back to the surface at a rate dependent on
M. Zeinstra-Helfrich and A. J. Murk