Case: Togo Figure 1 Location of the project. Image courtesy: maps.com; eosnap.com; Google Earth.
Case: Togo (2) Exposure of beachrocks Unusuallength of formation (>100km) Data availabilitythroughcontinuousobservation A uniquecombination of system boundaries
Research proposal Research topics Beachrocks & shoreline movement Controls Initialgeometry Formation of beachrocks Weathering of beachrocks Diageneticprocesses Controls Geomorphological setting Destructionrates Impact ondynamicequilibrium Shoreline response Response to low-crestedstructures
Research proposal (2) “Weathering of beachrock remains a ratheruntouched topic” (Gischler, 2007) Area of focus
Research proposal (3) Formation vs. destruction Whystudyweathering of beachrock (and notitsformation)? What is the potential and reliabilityof beachrock as a paleoenvironmental indicator? (e.g. tsunamis) Scientific How long will the beachrock in Togo continue to protect the shoreline? (Coastal) Engineering Can we use beachrock,naturalorartificial, in anecodynamicapproachto shoreline protection? Can we predict the occurrenceand characteristics of beachrock in deltaïc settings? Oil & Gas What is the reservoir potentialof beachrock?
Research proposal(4) Research Question: What is the relationship between the evolution of the shoreline profile in Togo and the exposure and characteristics of beachrock along this shoreline since 1975, and how can we use this knowledge to predict the impact of beachrock on the shoreline evolution in the future? Research questions
Research proposal(5) Subquestions: (a) What is the provenance of beachrock along the coast of Togo and what are its characteristics in terms of geometry, cementation type/degree and discontinuities? (b) How has the Togo shoreline developed since the first exposure of beachrock in the 1980’s? (c) Is there a significant relationship between the answers to question (a) and (b)? (d) How does this relationship relate to existing theories concerning beachrock formation and can it be used to predict future shoreline evolution? Research questions
Methodology Microscale (cross-shorecross-section) Blivi (1998) Amieux et al (1999) Blivi (1998)
Methodology Mesoscale (a few hundred meters longshore) Microscale cross-sections Airborneimagery interpretation
Methodology Macroscale (multiple kilometers longshore) diagenesis: cement alteration in time Introduction of time component: multiple exposures in time Gradualchange in longshoredirection temporal variation
Methodology Macroscale (multiple kilometers longshore) On a macroscale, the relationshipbetweenweathering and beachrock characteristicswillbedifficult to examine. Other research opportunitiesinclude: Spatialvariation of (a) age, (b) width, (c) inclination; + rel. to regionalgeology 2. Influence of submergedlow-crestedstructureson shoreline development
Field Campaign Planning Field Campaign term: 02.05.2011-20.06.2011 Upon Return:
Goals of the Project The goals of this project can be denoted as follows: A. Understanding processes in beachrock formation and erosion Understanding how the physical and geometrical characteristics of beachrock affect itserosion; Investigating how this fits in the existing theories of beachrock formation. B. Defining an erosion prognosis and identifying weak zones in shoreline Given the knowledge in goal A; Determining how erosion will continue in the near future; Identification of weak zones related to the characteristics of the beachrock in place. C. Defining an ecodynamic approach to shoreline protection For the case of Togo and similar cases; Defining a shoreline protection approach that takes into account, and benefits from the results of goal A. Image courtesy ggpht.com
Workingtowards the goals In tropic to subtropicregions, beachrock formation is likely to occur. Exposed beachrocks canfixate a shoreline, reducingitscapacity to maintaincoastlineequilibrium, inducinglateralshiftingof shoreline retreat. Betterunderstanding of regionalgeologycan help in determining the probability of beachrock occurrence Intermediateobservations
Topics of furtherattention Details and impact of multiple exposuresthrough time Diageneticmineralogicalsequence Bacterial and chemicalaction Variability of wave energy (lateral and spatial)
Modelling? Microscale: 2D cross-shore model (Xbeach?) Wave impact Influencetop surface to MSL oncross-shore sediment transport Mesoscale: 3D/ depth-averaged (Delft3D?) Wave energy distribution withdifferentialweathering cf. Ranasinghe and Turner (2006): Shoreline response to submergedstructures: A review
Field campaignfinances * Universiteitsfonds and KIVI NIRIA fund are not confirmed. In case of non-approval, own contribution will be raised and additional sources of funding will be sought after. ** The student’s continued expenses in The Netherlands (housing, university fees) are not taken into account in this overview.
Relevant literature Amieux, P. (1989), "Cathodoluminescence of carbonate-cemented Holocene beachrock from the Togo coastline (West Africa): an approach to early diagenesis," Sedimentary Geology, vol. 65, pp. 261-272. Blivi, A. (1998). "Quelques aspects du beach-rock dans le golfe du Bénin : le cas du Togo." Revue Cames: 43-56. Gischler, E. (2007). "Beachrock and intertidal precipitates." Geochemical sediments & Landscapes. In Blackwell Publishing: 365–390. Kindler, P. and R. Bain (1993). "Submerged upper Holocene beachrock on San Salvador Island, Bahamas: implications for recent sea-level history." GeologischeRundschau82(2): 241-247. Rossi, G. (1988). "The beach-rock: a natural protection against coastal erosion." Un example d'utilisationd'unedefensenaturellecontrel'erosionlittorale: le gres de plage37(1): 1-10. Vousdoukas, M. I., A. F. Velegrakis, et al. (2009). "Morphology and sedimentology of a microtidal beach with beachrocks: Vatera, Lesbos, NE Mediterranean." Continental Shelf Research 29(16): 1937-1947. Vousdoukas, M. I., A. F. Velegrakis, et al. (2007). "Beachrock occurrence, characteristics, formation mechanisms and impacts." Earth-Science Reviews 85(1-2): 23-46.