Building in water, also known as maritime construction (not to be confused with either marine engineering or water engineering) has for a long time been thought to be the forte of over-educated specialists. Just to be clear, marine engineering refers to the engineering of boats, ships, and other marine vessels or structures including pipelines and oil rigs. Water engineering, on the other hand, is more concerned with the design and building of water reticulation, treatment, and storage systems, among other related infrastructure.
Back to maritime construction; is it practical to build civil engineering structures in water? The short answer is yes, and this is quite common, especially in port infrastructure projects. It is thus proper to define the types of civil engineering structures that can be built in the marine environment.
1. Breakwaters
A breakwater is a major permanent coastal engineering structure designed to mitigate or “break” the force of waves on a harbor. This breaking of waves provides a sheltered area where boats and ships can moor or dock, commonly known as a harbor. The seaward side of a breakwater is usually protected by various layers of armor rock or protective concrete barriers that may have different shapes designed to increase lock on wave impact.
The cross-section of a breakwater usually consists of different layers and sizes of rock embedded upon each other. The outer (armor) layer consists of the largest and heaviest stones while the inner layers may consist of rubble rock that is less resistant to wave impact.
2. Jetties
A jetty, such as the one shown in the headline image, is a structure that projects from land out into the water. Its purpose is to serve as a walkway from a beach to vessels docked in the water, or as a landing platform for boats and smaller ships. Jetties need to be built on a foundation and these can either be concrete, steel, or wooden piles. A pontoon jetty doesn’t have a conventional piled foundation and is instead laid on pontoons that are connected together.
3. Marina
A marina can be thought of as a “small port” with provisions for the docking and mooring of boats, yachts, and other smaller vessels. A marina can extend seaward or, like the English Point Marina, it can be built along the shoreline. The building methodology is like that of a jetty, with either piled foundations or pontoons for support.
5 Key considerations to keep in mind when building in water
Building in the marine environment comes with a more stringent set of challenges when compared to building on the terrestrial environment. The key design principle is to provide a solid foundation for the structure, or a means of anchoring the structure to resist wind and wave action. Here are the key considerations before undertaking a building project on water.
1. The wave environment
Waves can be of two major types – wind-generated waves and tidal waves. Both types have a big impact when building in ocean environments compared to smaller water bodies such as lakes or the sea. Ideally, you should only ocean-build in a well-sheltered area, such as a natural harbor (a good example is Mombasa where the English Point Marina is located), or where a breakwater has already been built.
2. The geotechnical underwater profile
Similar to building on the land, the geotechnical profile of the sub-strata is a key component of maritime construction. This is crucial for both breakwaters that require a massive amount of rock and fill to be placed on the soil strata thus inducing new surcharge loading, or jetties that require piling. Clayey profiles may need piles to be drilled deeper, while sand and rock foundations are more stable and thus require less depth due to increased pile friction.
3. Salinity
Building in the ocean environment requires extra protection measures since the saline environment can degrade construction materials such as concrete and steel, for example, through corrosion. On the other hand, non-saline environments such as lakes and rivers provide less of a challenge. Extra measures have to be taken when building in saline environments, for example, using special concrete or coating steel with aluminium or zinc, coupled with cathodic protection.
4. The Project location
Maritime projects tend to be very expensive, especially where location is a factor. This is because not all the required good quality and approved material may be available near the project site, and may further need to be hauled through great distances.
5. Budget
Generally, maritime construction projects tend to have a higher construction cost, except for small wooden jetties. Costs may escalate due to the required expertise, special material, equipment such as barges and dredgers, and extended survey periods pre-construction.
