Coastal engineering

This week we’ve asked our coastal and marine engineer Ollie Poynter about the process used when considering coastal protection. Whilst a complicated technical area, we do follow a structured process to step through coastal management and investigation stages. A typical coastal engineering process involves:

1. Strategic Definition: Developing a large-scale Coastal Management Program or Coastal Hazard Adaptation Strategy over an entire coastline.

2. Preparation and Briefing: Developing a strategic Environment Management Plan or Shoreline Erosion Management Plan for discrete sediment cells

3. Concept Design and appraisal: Reviewing the coastal issues and potential mitigation options at a specific coastline.

4. Detailed Design: Refine the concept and prepare pre-construction information.

As design engineers, we are normally involved in Steps 2-4, and are often engaged when a site is already experiencing erosion. Our first task is to investigate the local coastal processes to understand why the site is eroding, overtopping or becoming inundated. This information is also used to ensure our designs will minimise future impacts, e.g. by designing for potential downdrift erosion or coastal squeeze. Coastal processes are assessed using a combination of design calculations and numerical models, the latter now a common tool for any coastal assessment. This will include the modelling of:

• Tides

• Currents

• Storm surges

• Wind

• Swell Waves

• Wind-generated waves

• Boat wake waves

When we look at protecting an area against erosion, wave overtopping or coastal inundation, there are a wide range of options available. These range from ‘hard’ structures like seawalls, to ‘soft’ options such as nature-based approaches. Some typical options include:

• Revegetation

• Beach Nourishment

• Rock fillets and mangrove restoration

• Vegetated seawall

• Geotextile Sand Container (GSC) Revetment

• Breakwaters and groynes

• Levees

Supporting the design process is an options appraisal, where we consider site constraints. Some of the things we need to consider when designing in the marine environment are:

• Available materials: We need to determine material sources that are available for the construction phase that can be transported and delivered to site.

• Access: We identify potential access constraints, practical and safe access will influence the design approach and structure type specified.

• Local environment and ecology:

• Wave and tidal climate: We consider wave and tidal conditions in the nearshore. These can be typical conditions or resulting from extreme weather and can have adverse effects during the design life.

• Marine plants and other protected habitats. We need to consider local flora and fauna at the site and how it will evolve in the future, and take care to minimise any ‘coastal squeeze’.

• Climate Change and adaptable designs. These days our designs need to be flexible, able to be upgraded in the future due to increasing sea levels or changing coastal forces.

• Budget: We need to be pragmatic when considering the likely budget for a project. Recognising a clients appetite for risk and constraints when developing a design is critical in setting the functional requirements.

• Maintenance and operation: All of the points above feed into maintenance. Develop a design that mitigates and/or minimises risks to public, environment, and maintenance operations.