beachrocks in togo progress report

18-04-2023

Challenge the future

DelftUniversity ofTechnology

Beachrocks in TogoProgress reportGuido Rutten

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


Case: Togo

Figure 1 Location of the project. Image courtesy: maps.com; eosnap.com; Google Earth.


Case: Togo (2)

• Exposure of beachrocks

• Unusual length of formation (>100km)

• Data availability through continuous observation

A unique combination of system boundaries


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


Research proposal (2)

“Weathering of beachrock remains a rather untouched topic”

(Gischler, 2007)

Area of focus


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?



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



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


MethodologyProcess flow


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


MethodologyDominant parameters

ROCK MASS

Grains

Type

Size & Distribution

Sorting

Cement

Type

Texture

Age

Void Space

(porosity)

(permeability)

GEOMETRY


Width (cross-shore)

Thickness

Length (longshore)

Inclination


“Wave energy”

Angle of incidence



Salinity

Bacterial action

integrationover time


MethodologyScale approach

ROCK MASS

Grains

Type

Size & Distribution

Sorting

Cement

Type

Texture

Age

Void Space

(porosity)

(permeability)

GEOMETRY


Width (cross-shore)

Thickness

Length (longshore)

Inclination


“Wave energy”

Angle of incidence



Salinity

Bacterial action

Microscale

Togo Case Mesoscale Generic

Macroscale


MethodologyMicroscale (cross-shore cross-section)

ROCK MASS

Grains

Type

Size & Distribution

Sorting

Cement

Type

Texture

Age

Void Space

(porosity)

(permeability)

GEOMETRY


Width (cross-shore)

Thickness

Length (longshore)

Inclination


“Wave energy”

Angle of incidence



Salinity

Bacterial action

Blivi (1998)

Amieux et al (1999)

Blivi (1998)


MethodologyMesoscale (a few hundred meters

longshore)

ROCK MASS

Grains

Type

Size & Distribution

Sorting

Cement

Type

Texture

Age

Void Space

(porosity)

(permeability)

GEOMETRY


Width (cross-shore)

Thickness

Length (longshore)

Inclination


“Wave energy”

Angle of incidence



Salinity

Bacterial action

Microscale cross-sections

Airborne imageryinterpretation


MethodologyMacroscale (multiple kilometers

longshore)

ROCK MASS

Grains

Type

Size & Distribution

Sorting

Cement

Type

Texture

Age

Void Space

(porosity)

(permeability)

GEOMETRY


Width (cross-shore)

Thickness

Length (longshore)

Inclination


“Wave energy”

Angle of incidence



Salinity

Bacterial action

Introduction of time component:

multiple exposures in time

temporal variation

Gradual change in longshore direction

diagenesis: cement alteration in time


MethodologyMacroscale (multiple kilometers

longshore)

ROCK MASS

Grains

Type

Size & Distribution

Sorting

Cement

Type

Texture

Age

Void Space

(porosity)

(permeability)

GEOMETRY


Width (cross-shore)

Thickness

Length (longshore)

Inclination


“Wave energy”

Angle of incidence



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


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)


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


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.


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


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)


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


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.


Checklist before departure

Logistics: Visa Medical Housing Cooperation local contacts

Research: Reservations for laboratory Regional geology assessment Sampling procedure


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


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.