National Network of Regional Coastal Monitoring Programmes

UNALINEA

Introduction

UnaLinea is a state-of-the-art model that simulates the evolution of the plan shape of a beach. The beach plan shape is determined by the position of a single contour, therefore making UnaLinea a "one-line model". UnaLinea uses a formulation of total longshore transport rate based on the widely used CERC formula. The model changes the coastline every time step, allowing for the correct simulation of the changing drift rates with time.

A typical application of this model would be to study the impact that different interventions to the fluvial load will have in the adjacent coast in a medium to long term time.

The accompanying user manual provides a guide on how to use the model itself.

Predecessor version

The predecessor tool had been derived by HR Wallingford as part of the FRMRC2 project, as a simplified, regional-scale one-line model of wave-driven beach plan-shape evolution, implemented in Fortran as a finite difference solution of the continuity equation for sediment (Stripling et al, 2011). The model assumes an average beach slope and does not consider short term changes in the beach profile. Offshore wave conditions are transformed into the position of breaking at each point along the beach. These breaking wave conditions are used to calculate the longshore drift at each of these points. The cross-shore change in position of the specified contour is calculated from longshore gradients in the wave induced longshore transport rate (see Figure 1).

Figure 1. Schematisation of the grid in UnaLinea

Due to the fact that the profile remains unchanged, the shoreline position moves forward or backward, according to the longshore drift gradients, translating the profile, as shown in Figure 2.

The effects of engineering structures and active beach management techniques, such as beach nourishment or losses to offshore, may be included in the model, as may a simple representation of cliff erosion (Stripling and Panzeri 2009, Stripling et al, 2011).

Figure 2. Profile schematisation in UnaLinea and symbolic erosion and accretion

Capabilities

UnaLinea models the following processes:

Wave transformation:

refraction
shoaling

Fluvial interaction:

sediment input from rivers
sediment losses offshore

Sediment transport:

CERC formula
Damgaard and Soulsby (1997) formula

Active beach management techniques:

beach renourishment
beach mining
losses

The beach plan shape is specified by the position of a single contour, usually either Mean Water Level or a particular high tide level. The model assumes an average beach slope and does not consider short term changes in the beach profile. Offshore wave conditions are refracted into the position of breaking at each point along the beach. These breaking wave conditions are used to calculate the longshore drift at each of these points. The change in position of the specified contour is calculated from differences in the wave induced longshore transport.

In the presence of groynes, the sediment transport is considered zero at the groyne position, acting as an impermeable barrier.

The UnaLinea model has been designed as a first-stage tool in understanding the behaviour of a coast and the impact of engineering works upon it. Its relative simplicity and ease of use allow the model to be used by non-specialist engineers with a minimum of data, as well as allowing more detailed investigations by more experienced users.

For iCOASST the model was made OpenMI compatible.

Application of Unalinea Model to iCOASST pilot sites and lessons learnt

UnaLinea has been applied to the Liverpool pilot site in two instances, one for the Blackpool frontage and another one for the Formby frontage, with the Ribble estuary in the middle of both being represented in ASMITA. The composition is described in detail here

Evaluation for end-users

As part of the Environment Agency project "Embedding iCOASST into practice", HR Wallingford have undertaken an independent evaluation of the usability of the iCOASST models. Each of the models have been downloaded from this website, compiled and run using (i) the documentation and (ii) the site-specific data sets on which they have been developed (also provided on this website). The outcome of this evaluation for this model can be found here and should be referenced by anyone interested in using or developing the model further.

Download Model

A general description of the input and output files is given here, although a detailed description of each of the input and output files is provided in the user manual.

Input data

UnaLinea requires mainly two sets of input data:

Model data: contains values for the different parameters and variables needed in order to set the model up. Data such as the depth of closure or the positions and sediment loadings of river are contained within the model data set.
Wave data: contains time-series of wave conditions in shallow water.

In order to model the littoral sediment transport, and its medium- to long-term response to the fluvial load, nearshore wave data covering several decades is required.

UnaLinea can be run either deterministically, or in a stochastic manner (as is required here for dealing with coastal-fluvial sediment transport interaction). When UnaLinea is run stochastically, minimising processing time is important, as this methodology involves running the numerical model UnaLinea of the order of thousands of times. Input time series with hourly (or even three-hourly) conditions and grid spacing of the order of 10-25m is therefore prohibited. Input filtering is then required in order to increase the time-step of the time-series.

Output data

UnaLinea provides mainly two types of output data:

Shoreline development: position of the shoreline on the specified output times, as well as the maxima, minima and average shoreline positions throughout the run.
Drift rates: longshore drift values along the beach on each of the specified output times, as well as the maxima, minima and average drifts throughout the run.

Licence/conditions

This model is distributed under the GPL licence:

https://www.gnu.org/licenses/gpl.html

Download Data

Example input/output files and user manuals are included with the model files and can be downloaded from the UNALINEA Download Model tab. The iCOASST model results from UNALINEA form part of the Liverpool Bay composition files.

Licence/conditions

These model data files are distributed under the Open Government Licence:

http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/

References

Damgård JS and RL Soulsby (1997). Longshore bed-load transport. Proc. 25th Int. Conf. Coastal Engineering. 3, pp. 3614-3627. ASCE.

Stripling, S. and Panzeri, M.C. (2009). "Modelling shoreline evolution to enhance flood risk assessment." Proceedings of the ICE - Maritime Engineering, 162(3) 137-144.

Stripling S, Panzeri M, Blanco B et al. (2011). "Broad scale integration of coastal flood and erosion risk models." FRMRC2 Work Package 4.3 Science Report. http://web.sbe.hw.ac.uk/frmrc/ (accessed 04/02/2015).

Contact

Dr James Sutherland (HR Wallingford) is the current point of contact for UNALINEA

j.sutherland@hrwallingford.com

Direct Message

Message Dr James Sutherland directly

National Network of Regional Coastal Monitoring Programmes

UNALINEA

Introduction

Predecessor version

Capabilities

Application of Unalinea Model to iCOASST pilot sites and lessons learnt

Evaluation for end-users

Download Model

Input data

Output data

Licence/conditions

Download Data

Licence/conditions

References

Contact

Direct Message

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