RegMeasures
commented
5 years ago In Donnelly et al (2006) it seems like there is some basis for taking a very simplistic approach to calculating overwash sediment flux (per unit length along the beach), qs as a function of overwash potential, OP, with something like: qs = α(OP)n
where: OP = R2% + η - hc α and n are coefficients (n~2 except this formula is based for a wave by wave calculation rather than using R2%*...).
I could then partition between depositing on top of barrier (i.e. overtopping) or back of barrier (i.e. overwashing) by coming up with some sort of simple approach based on the fact that:
For OP<0.5 m, overtopping (80%) is more likely than overwashing (20%), while the reverse is true for OP>0.5 m (24% overtopping and 76% overwashing).
(Matias et al 2012)
I may have to include some sort of deficit volume element to the distribution effect as well to account for the fact a narrow barrier is more easily overwashed.
References
Donnelly C., Kraus N., Larson M. (2006) State of Knowledge on Measurement and Modeling of Coastal Overwash. J Coast Res 224(4):965–991. https://www.jcronline.org/doi/abs/10.2112/04-0431.1
Matias A., Williams J.J., Masselink G., Ferreira Ó. (2012) Overwash threshold for gravel barriers. Coast Eng 63:48–61. http://www.sciencedirect.com/science/article/pii/S0378383911001980
The model of Lorenzo-Trueba and Ashton (2014) looks like it provides a simple basis for tracking barrier geometry - either with or without the shoreface slope component included? (maybe without to start with). Their simplified cross-shore profile responds to overwashing by retreat of the shoreface (I could retreat it all the way down to the close depth?) and corresponding increase to the barrier height and/or back barrier position as shown below:
(Fig 3c, Lorenzo-Trueba and Ashton, 2014)
The model overwash fluxes are however simply driven by defecit volumes, rather than wave timeseries, so are not suitable for my model. Although potentially I could use the defecit volume approach for partitioning of overwash (if I had no better option - it would be nice to have this wave condition dependent...). The approach requires an estimated equilibrium barrier width, We, and equilibrium barrier height, He, Based on these parameters it is then possible to calculate top-barrier deficit volume, Vd,H, and back-barrier deficit volume, Vd,B (per unit shoreline length). Lorenzo-Trueba and Ashton (2014) assume overwash rate is proportional to defecit volume (limited by a max overwash rate), and distributed between top and back barrier based on the relative defecit volumes.
(Fig 4, Lorenzo-Trueba and Ashton, 2014)
References
Lorenzo-Trueba J., Ashton A.D. (2014) Rollover, drowning, and discontinuous retreat: Distinct modes of barrier response to sea-level rise arising from a simple morphodynamic model. J Geophys Res Earth Surf 119.