beachrocks in togo progress report
TRANSCRIPT
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18-04-2023
Challenge the future
DelftUniversity ofTechnology
Beachrocks in TogoProgress reportGuido Rutten
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2Beachrocks in Togo – Progress April 12th
Timeline
November Literature study An extensive literature study has been carried out in order to provide the theoretical background to formulate a research proposal.
December
January 2011 Preparation of proposals
February Finalization of proposal Choice of topic and definition of field campaign
Fieldwork preparation Finances, dates, local contactsMarch Data collection Gathering of available data (reports, airborne
imagery, borehole data)Data processingApril Modeling Set-up of a model in Delft3D software,
Formulation of hypotheses
Development of theoretical models, derivation of fieldwork plan
Detailed fieldwork plan
May 2nd – June 20th Field campaign Field campaign in Togo
June Synthesis Processing of field observationsReport-writing
July/August Presentation
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Case: Togo
Figure 1 Location of the project. Image courtesy: maps.com; eosnap.com; Google Earth.
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Case: Togo (2)
• Exposure of beachrocks
• Unusual length of formation (>100km)
• Data availability through continuous observation
A unique combination of system boundaries
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Research proposal
Formation of beachrocks
Research topics
Beachrocks &shoreline movement
Weathering of beachrocks
Controls Initial geometry
Response to low-crested structures
Shoreline response
Geomorphological setting
Impact on dynamic equilibrium
Destruction rates
Diagenetic processes Controls
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6Beachrocks in Togo – Progress April 12th
Research proposal (2)
“Weathering of beachrock remains a rather untouched topic”
(Gischler, 2007)
Area of focus
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Research proposal (3)Formation vs. destruction
Why study weathering of beachrock (and not its formation)?
How long will the beachrock in Togo continue to protect the shoreline?
Scientific
What is the potential and reliability of beachrock as a paleoenvironmental indicator? (e.g. tsunamis)
(Coastal)Engineering Can we use beachrock, natural or artificial, in an
ecodynamic approach to shoreline protection?
Oil & Gas
Can we predict the occurrence and characteristics of beachrock in deltaïc settings?
What is the reservoir potential of beachrock?
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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
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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
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10Beachrocks in Togo – Progress April 12th
MethodologyProcess flow
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Methodology
ROCK MASS
Grains
Type
Size & Distribution
Sorting
Cement
Type
Texture
Age
Void Space
(porosity)
(permeability)
GEOMETRY
Top surface (ref to MSL)
Width (cross-shore)
Thickness
Length (longshore)
Inclination
WEATHERING & EROSION IMPACTS
“Wave energy”
Angle of incidence
Sunlight/Δtemperature
Δpressure (cross-shore)
Salinity
Bacterial action
Dominant parameters
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MethodologyDominant parameters
ROCK MASS
Grains
Type
Size & Distribution
Sorting
Cement
Type
Texture
Age
Void Space
(porosity)
(permeability)
GEOMETRY
Top surface (ref to MSL)
Width (cross-shore)
Thickness
Length (longshore)
Inclination
WEATHERING & EROSION IMPACTS
“Wave energy”
Angle of incidence
Sunlight/Δtemperature
Δpressure (cross-shore)
Salinity
Bacterial action
integrationover time
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MethodologyScale approach
ROCK MASS
Grains
Type
Size & Distribution
Sorting
Cement
Type
Texture
Age
Void Space
(porosity)
(permeability)
GEOMETRY
Top surface (ref to MSL)
Width (cross-shore)
Thickness
Length (longshore)
Inclination
WEATHERING & EROSION IMPACTS
“Wave energy”
Angle of incidence
Sunlight/Δtemperature
Δpressure (cross-shore)
Salinity
Bacterial action
Microscale
Togo Case Mesoscale Generic
Macroscale
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MethodologyMicroscale (cross-shore cross-section)
ROCK MASS
Grains
Type
Size & Distribution
Sorting
Cement
Type
Texture
Age
Void Space
(porosity)
(permeability)
GEOMETRY
Top surface (ref to MSL)
Width (cross-shore)
Thickness
Length (longshore)
Inclination
WEATHERING & EROSION IMPACTS
“Wave energy”
Angle of incidence
Sunlight/Δtemperature
Δpressure (cross-shore)
Salinity
Bacterial action
Blivi (1998)
Amieux et al (1999)
Blivi (1998)
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MethodologyMesoscale (a few hundred meters
longshore)
ROCK MASS
Grains
Type
Size & Distribution
Sorting
Cement
Type
Texture
Age
Void Space
(porosity)
(permeability)
GEOMETRY
Top surface (ref to MSL)
Width (cross-shore)
Thickness
Length (longshore)
Inclination
WEATHERING & EROSION IMPACTS
“Wave energy”
Angle of incidence
Sunlight/Δtemperature
Δpressure (cross-shore)
Salinity
Bacterial action
Microscale cross-sections
Airborne imageryinterpretation
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16Beachrocks in Togo – Progress April 12th
MethodologyMacroscale (multiple kilometers
longshore)
ROCK MASS
Grains
Type
Size & Distribution
Sorting
Cement
Type
Texture
Age
Void Space
(porosity)
(permeability)
GEOMETRY
Top surface (ref to MSL)
Width (cross-shore)
Thickness
Length (longshore)
Inclination
WEATHERING & EROSION IMPACTS
“Wave energy”
Angle of incidence
Sunlight/Δtemperature
Δpressure (cross-shore)
Salinity
Bacterial action
Introduction of time component:
multiple exposures in time
temporal variation
Gradual change in longshore direction
diagenesis: cement alteration in time
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17Beachrocks in Togo – Progress April 12th
MethodologyMacroscale (multiple kilometers
longshore)
ROCK MASS
Grains
Type
Size & Distribution
Sorting
Cement
Type
Texture
Age
Void Space
(porosity)
(permeability)
GEOMETRY
Top surface (ref to MSL)
Width (cross-shore)
Thickness
Length (longshore)
Inclination
WEATHERING & EROSION IMPACTS
“Wave energy”
Angle of incidence
Sunlight/Δtemperature
Δpressure (cross-shore)
Salinity
Bacterial action
On a macroscale, the relationship between weathering and beachrock characteristics will be difficult to examine.
Other research opportunities include:
1. Spatial variation of (a) age,(b) width,(c) inclination;+ rel. to regional geology
2. Influence of submerged low-crested structures on shoreline development
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Field CampaignPlanning
Week Phase Activities1 Acclimation Check housing, transportation
Local Contact Visit local contactsDiscuss practicalities of phase IIArrange transport for phase II
2 Phase I: Interview local expertsUsing Local Data Sources Review local literature and data
3 Phase II: Visits site 1 to 6On-site geological investigation
4 Phase III: Process data Phase I and Phase IIPreliminary consistency check Check consistency of data
Validate assumptionsFeedback with local experts
5 Phase IV: Additional site visitsAdditional on-site investigationWrap-up Final meeting local experts
6 Back-up Back-up days for delays
Field Campaign term: 02.05.2011-20.06.2011
Upon Return:Sample preparation Prepare cores, thin sections
Sample interpretation Microscopy, Dating (VU), Cathodoluminiscence (VU)
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Field CampaignActivities
Activity Subset Quantity per site
Parameters
Weathering Mapping
Depth of weathering
2 cross-sections By colour; depth; continuity
Potholes5 sample areas (1m2)
# per surface unit; depth; diameter
Diaclases1 sample area (9 m2)
# per surface unit; length; depth; aperture
Rock Mass Strength Testing
Schmidt Hammer 20 measurements Reference value; related to fabric zones
Sampling Up to 3
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Image courtesy ggpht.com
Goals of the Project
The goals of this project can be denoted as follows:
A. Understanding processes in beachrock formation and erosionUnderstanding how the physical and geometrical characteristics of beachrock affect
its erosion; 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 protectionFor the case of Togo and similar cases; Defining a shoreline protection approach
that takes into account, and benefits from the results of goal A.
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Working towards the goals
(1) In tropic to subtropic regions, beachrock formation is likely to occur.
(2) Exposed beachrocks can fixate a shoreline, reducing its capacity to maintain coastline equilibrium, inducing lateral shifting of shoreline retreat.
(3) Better understanding of regional geology can help in determining the probability of beachrock occurrence
Intermediate observations
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Topics of further attention
(1) Details and impact of multiple exposures through time
(2) Diagenetic mineralogical sequence
(3) Bacterial and chemical action
(4) Variability of wave energy (lateral and spatial)
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Modelling?
• Microscale: 2D cross-shore model (Xbeach?)• Wave impact• Influence top surface to MSL on cross-shore sediment
transport
• Mesoscale: 3D/ depth-averaged (Delft3D?)• Wave energy distribution with differential weathering• cf. Ranasinghe and Turner (2006): Shoreline response to
submerged structures: A review
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Field campaign finances
Expenses Costs Funding AmountFlight AMS-ACC v.v. 850€ Own contribution 400€Transfer Accra - Lomé v.v. 50€ Parents 250€Accommodation 40 nights 500€ KIVI NIRIA fund* 500€Costs of living 40 days 400€ Section TU Delft 500€Local transport 280€ Universiteitsfonds* 500€Visa 70€
Total 2150€** Total 2150€
* 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.
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Checklist before departure
Logistics: Visa Medical Housing Cooperation local contacts
Research: Reservations for laboratory Regional geology assessment Sampling procedure
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Weathering processes
• Physical weathering• Abrasion – depends on properties of moving particles• Crystal growth• Thermal expansion• Stress release• Hydraulic action• Biological weathering• Antropogenic
• Chemical weathering• Dissolution• Hydration• Hydrolysis• Oxidation• Biological
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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." Geologische Rundschau 82(2): 241-247.Rossi, G. (1988). "The beach-rock: a natural protection against coastal erosion." Un example d'utilisation d'une
defense naturelle contre l'erosion littorale: le gres de plage 37(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.