6 results on '"Shadrick, Jennifer R."'
Search Results
2. Quantifying coastal cliff retreat in response to climate change using cosmogenic radionuclides and numerical modelling
- Author
-
Shadrick, Jennifer R., Rood, Dylan, and Piggott, Matthew
- Abstract
The response of coasts to climate change is an uncertain threat to the infrastructure and inhabitants in these areas. Rock coasts are ubiquitous landscapes found along coastlines worldwide and are often sites of important infrastructure, which are vulnerable to coastal erosion and cliff retreat. Furthermore, the stability of rock coasts is threatened by future climate change, particularly the influence of accelerating sea level rise and increased storminess. Constrains need to be placed on past erosion rates at rock coasts across millennial timescales in order to better forecast how future cliff retreat rates will respond to climate change. The ability to quantify coastal cliff retreat rates across millennial timescales has been transformed with the application of exposure dating across shore platforms using cosmogenic radionuclide (CRN) analysis. Previous studies have successfully quantified long-term cliff retreat rates across the Holocene for a range of rock coast sites; however, previous work has been limited by the use of a simplistic geometric-based model to interpret CRN concentrations. Considerable potential remains in the use of CRN analysis along rock coasts. In this thesis, first, I develop a routine that is the first application of a process-based model to interpret CRN concentrations. Next, I apply this technique to a range of rock coast sites across the UK to quantify long-term, transient cliff retreat rates for the past and also make forecasts for the future to better understand the response of rock coasts to climate change. A multi-objective optimisation routine is developed in order to optimise a process-based model to both measured topographic and CRN concentration data for two sandstone sites in the UK. The results highlight that the multi-objective optimisation routine improves model results by reducing equifinality to constrain uncertainties and produce consistent trends in transient long-term cliff retreat rates. This approach is employed to quantify long-term, transient cliff retreat rates for the past 7,000 years at two sandstone rock coast sites. These long-term cliff retreat rates clearly link to the rate of relative sea level rise at both sites. I also use the process-based model to decode insights into the key erosional processes involved in rock coast evolution. Next, I use the optimised parameters from the process-based model results to make forecasts of future cliff retreat rates to the year 2100 using future sea level rise scenarios. At both sandstone sites, cliff retreat forecasts are likely to accelerate by 3-7 times present-day rates, to maximum retreat rates of 22-30 cm yr-1, using the current trajectory of relative sea level rise. Comparisons to cliff retreat rates quantified for the past reveal that these projected cliff retreat rates are unprecedented in the last 3-5 millennia for both sites. These results highlight that even historically stable rock coasts are highly sensitive to sea level rise and need to be included in future planning. Finally, I apply the newly developed optimisation routine to four new chalk rock coast sites on the south coast of England to quantify long-term cliff retreat rates across the late-Holocene. My results identify a recent acceleration in cliff retreat rates, and such rapid cliff retreat rates last occurred 5300-6800 years ago. Furthermore, the optimised, process-based model detects significantly different dominant factors controlling erosion between the sandstone and chalk rock coast sites. Model results for the chalk sites also suggest that heterogeneous lithology and beach material play an important role in the long-term erosion at these sites, and advocates for the inclusion of these factors into future process-based rock coast evolution models. Overall, the results presented in this thesis highlight the knowledge gained from implementing a process-based model to interpret CRN concentrations and quantify transient cliff retreat rates across millennial timescales. Through the methods that I develop, the expected relationship between long-term cliff retreat rates and the rate of sea level rise is supported with empirical data for the first time. Multi-objective optimisation improves model equifinality, which allows for more accurate and well constrained past and future cliff retreat rate forecasts. Results clearly demonstrate the power and utility of these methods to better understand rock coast response to climate change and make more reliable forecasts of cliff retreat rates at coastlines worldwide.
- Published
- 2022
- Full Text
- View/download PDF
3. Sea-level rise will likely accelerate rock coast cliff retreat rates
- Author
-
Shadrick, Jennifer R., Rood, Dylan H., Hurst, Martin D., Piggott, Matthew D., Hebditch, Bethany G., Seal, Alexander J., and Wilcken, Klaus M.
- Published
- 2022
- Full Text
- View/download PDF
4. Constraints on long-term cliff retreat and intertidal weathering at weak rock coasts using cosmogenic 10Be, nearshore topography and numerical modelling.
- Author
-
Shadrick, Jennifer R., Rood, Dylan H., Hurst, Martin D., Piggott, Matthew D., Wilcken, Klaus M., and Seal, Alexander J.
- Subjects
- *
CLIFFS , *WEATHERING , *CHALK , *TOPOGRAPHY , *BEACHES , *ABSOLUTE sea level change , *LONG-Term Evolution (Telecommunications) , *COASTS - Abstract
The white chalk cliffs on the south coast of England are one of the most iconic coastlines in the world. Rock coasts located in a weak lithology, such as chalk, are likely to be most vulnerable to climate-change-triggered accelerations in cliff retreat rates. In order to make future forecasts of cliff retreat rates as a response to climate change, we need to look beyond individual erosion events to quantify the long-term trends in cliff retreat rates. Exposure dating of shore platforms using cosmogenic radionuclide analysis and numerical modelling allows us to study past cliff retreat rates across the Late Holocene for these chalk coastlines. Here, we conduct a multi-objective optimisation of a coastal evolution model to both high-precision topographic data and 10Be concentrations at four chalk rock coast sites to reveal a link between cliff retreat rates and the rate of sea-level rise. Furthermore, our results strengthen evidence for a recent acceleration in cliff retreat rates at the chalk cliffs on the south coast of England. Our optimised model results suggest that the relatively rapid historical cliff retreat rates observed at these sites spanning the last 150 years last occurred between 5300 and 6800 years ago when the rate of relative sea-level rise was a factor of 5–9 times more rapid than during the recent observable record. However, results for these chalk sites also indicate that current process-based models of rock coast development are overlooking key processes that were not previously identified at sandstone rock coast sites. Interpretation of results suggest that beaches, cliff debris and heterogenous lithology play an important but poorly understood role in the long-term evolution of these chalk rock coast sites. Despite these limitations, our results reveal significant differences in intertidal weathering rates between sandstone and chalk rock coast sites, which helps to inform the long-standing debate of "wave versus weathering" as the primary control on shore platform development. At the sandstone sites, subaerial weathering has been negligible during the Holocene. In contrast, for the chalk sites, intertidal weathering plays an active role in the long-term development of the shore platform and cliff system. Overall, our results demonstrate how an abstract, process-based model, when optimised with a rigorous optimisation routine, can not only capture long-term trends in transient cliff retreat rates but also distinguish key erosion processes active in millennial-scale rock coast evolution at real-world sites with contrasting rock types. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
5. Multi-objective optimisation of a rock coast evolution model with cosmogenic 10Be analysis for the quantification of long-term cliff retreat rates
- Author
-
Shadrick, Jennifer R., Hurst, Martin D., Piggott, Matthew D., Hebditch, Bethany G., Seal, Alexander J., Wilcken, Klaus M., and Rood, Dylan H.
- Abstract
This paper presents a methodology that uses site-specific topographic and cosmogenic 10Be data to perform multi-objective model optimisation of a coupled coastal evolution and cosmogenic radionuclide production model. Optimal parameter estimation of the coupled model minimises discrepancies between model simulations and measured data to reveal the most likely history of rock coast development. This new capability allows a time series of cliff retreat rates to be quantified for rock coast sites over millennial timescales. Without such methods, long-term cliff retreat cannot be understood well, as historical records only cover the past ∼150 years. This is the first study that has (1) applied a process-based coastal evolution model to quantify long-term cliff retreat rates for real rock coast sites and (2) coupled cosmogenic radionuclide analysis with a process-based model. The Dakota optimisation software toolkit is used as an interface between the coupled coastal evolution and cosmogenic radionuclide production model and optimisation libraries. This framework enables future applications of datasets associated with a range of rock coast settings to be explored. Process-based coastal evolution models simplify erosional processes and, as a result, often have equifinality properties, for example that similar topography develops via different evolutionary trajectories. Our results show that coupling modelled topography with modelled 10Be concentrations can reduce equifinality in model outputs. Furthermore, our results reveal that multi-objective optimisation is essential in limiting model equifinality caused by parameter correlation to constrain best-fit model results for real-world sites. Results from two UK sites indicate that the rates of cliff retreat over millennial timescales are primarily driven by the rates of relative sea level rise. These findings provide strong motivation for further studies that investigate the effect of past and future relative sea level rise on cliff retreat at other rock coast sites globally.
- Published
- 2021
6. Multi-objective optimisation of a rock coast evolution model with cosmogenic <sup>10</sup>Be analysis for the quantification of long-term cliff retreat rates
- Author
-
Shadrick, Jennifer R., primary, Hurst, Martin D., additional, Piggott, Matthew D., additional, Hebditch, Bethany G., additional, Seal, Alexander J., additional, Wilcken, Klaus M., additional, and Rood, Dylan H., additional
- Published
- 2021
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.