For people living in coastal areas, it is a fact of life that the sea “gives and takes”, meaning there are well known advantages and disadvantages to consider. The fact that it gives, is precisely the reason why living near the coast is so attractive. However, in terms of what it takes, there are also risks to consider, such as a constant threat of flooding and the possible loss of land, buildings, livestock and even human life.
Historically, these dangers were considered something that had to be accepted. However, as the demand for settling long-term along the coast grew in popularity, coupled with the increasing perception that measures could be taken to reduce risks, the principle of coastal protection emerged.
Hard sea defences
In the early stages, coastal protection was widely accomplished by creating hard sea defences. Seen to be the most obvious solution, it centred around the idea that in order to withstand the force of the sea, so-called hard material like rock and stone was required.
From the 18th century until the early part of the 20th century, many kilometres of hard sea defences were built around the world. However, over time, the disadvantages became increasingly obvious.
Primarily, the mining and transport of the required material, as well as the construction itself, became costly and time consuming. Additionally, it proved that even after completion, it still commanded high costs in terms of maintenance.
Another consideration was that hard defences were by their very nature rigid. That lack of flexibility meant they could not be easily adapted to altering circumstances, in regards to morphology, population density and climate change, for example.
Finally, but also of critical importance, there became a growing awareness that this type of defence was environmentally unsound. In other words, it was not considered to be a nature-friendly approach.
The importance of seagoing dredgers
In order to create and maintain soft sea defences, sand is a key requirement. It was the development of the seagoing trailing suction hopper dredger (TSHD) in the 20th century that made the mining, transport and application of sand for coastal protection feasible and cost-efficient.
The fact that TSHDs can dredge sand out at sea, transport it to the coast and apply it in different ways, makes them the main tool for creating and maintaining soft sea defences.
By the end of the 20th century, TSHDs were being used to carry out beach replenishments, involving the placement of sand by pumping it ashore to the precise location where the material was needed.
Studies carried out in The Netherlands proved that in several cases, the sand didn’t have to be put onto the beach itself to achieve a favourable result. In fact, the studies showed that supplying sand to the coastal system as a whole, for example in foreshore locations, is also a highly effective option. The principle consists of keeping a total amount in the coastal zone to maintain a balance that prevents the erosion from taking place.
Since the turn of the century, coastal protection in The Netherlands, as well as in many other countries, consists of a balanced combination of beach and foreshore combinations. Foreshore replenishments have the advantage of being less costly, due to the fact that pumping ashore is not necessary and the process can be carried out in much shorter timeframes.
In the case of foreshore replenishments, the hopper dredgers can apply the sand by dumping it through their bottom doors/valves or, when a split hopper is used, by splitting. The rainbow technique can also be used, often in combination with dumping.
Every size matters
Coastal protection is an activity in which hopper dredgers of all sizes can hold an important role. Large dredgers are highly efficient when sand has to be mined at long sailing distances. Smaller vessels can be to put to good use when a replenishment has to be carried out in shallow water.
Shallow draft hopper dredgers have the advantage of being able to approach closer to the coastline, as well as shorten sailing distances through their ability to pass over sandbanks.
The future of coastal protection
It is expected that due to climate change and subsequent morphological changes, for example rising sea levels, coastal protection is expected to become even more challenging.
As such, the dredging industry must keep focused on developing innovations with respect to equipment, as well as work methods.