A glimpse of Land Reclamation

It’s been a while since my first article which talk about my education background..

It is always very interesting to write about your education background, sometimes when I talk about my education background I feel like an expert.. :D (Is it natural or it is just me?)

I am a coastal engineer, who has experiences in coastal protection design and lucky me to be involved in 4 reclamation projects in my country (Indonesia).

In this opportunity, I want to share about land reclamation, which been one of my favorite job. J

Land reclamation is the process of creating new land from ocean, riverbeds, or, lake (Wikipedia). (For this article, I’m talking about reclamation in ocean)

Usually land reclamation is used for residential area or harbor. One of the most popular land reclamation is in Dubay (Palm Island).  This reclamation become famous because in the new land standing fabulous thousands villas and dozens hotels.

Palm island, Dubay (source: google.com)

 Nowadays, many countries are racing to make land reclamation. Population density can be one reason; increasing national income is another reason (I will not elaborate it more because I’m not the expert).

In my country Indonesia, the land reclamation mostly developed by private sector (with concession agreement from government) for commercial purpose of course. In Jakarta (Capital of Indonesia), the reclamation projects lies on the northern coast of Jakarta. Some of the projects are in construction stage now. Before the construction stage, the design of land reclamation should be in line with laws and regulation in Indonesia (Ijin Prinsip Reclamasi). << I didn’t elaborate this part also :D

What will I share here is about land reclamation component, and a little bit about construction method.

If we talk about land reclamation, we must think about:

·         With what it should be filled?

·         What is the bound material?

The ideal fill material for reclamation is sand with a degree of fines. The fill material cannot contain any peat, vegetation, timber, organic, soluble or perishable material, no dangerous, toxic or readily combustible material and no metal, rubber, plastic or any other synthetic material.

This material is almost always borrowed from offshore locations by dredging equipment (trailer suction hoppers or cutter dredgers). This is the most cost effective and fastest way of supplying large volumes of sand to a project site. The sand is dredged from the seabed from so-called sand-borrow areas. These sand-borrow areas need to be identified by sand search investigations

The bounds of land reclamation called a revetment. This revetment construct from rock or artificial material (from concrete). In every reclamation project, the sand material will be the same (same quality), but it is different for the material for revetment.

Revetment (source: google.com)

For simple, the design of revetment is depending on wave, tidal level, and seabed. They will determine the rock/concrete stability (size, mass), the height of revetment (so that the overtopping wave cannot (or can but in minimum amount) inundate the area behind the revetment. (If you want to know about this more, u can send me email, I will gladly explain it to you)

How to construct land reclamation?

 There are 3 main work items in land reclamation construction; discharging of sand fill, reclamation works and revetment construction.

At first the sand as a filling material for reclamation should be dredge and then spray to the reclamation site. In sand dredging (For collecting, transportation and discharging sand in the reclamation site), 3 methods are possible to do, using a Trailer Suction Hopper Dredger or using a stationary dredger support by tug boat and hopper/split barge or combination of both methods.

Dredging Vehicle (source: google.com)

After that, the next step is sand spraying. The sand spraying should be carried out very carefully. The method should be layer by layer (max half meter thick). This is done to prevent the squeeze and mud-waves. If this step not treated well, there will be some big problem in the settlements.

Sand Sraying (Rainbowing) (source: google.com)

After the sand spraying, the next step is the reclamation work. First, the sand layer is made. The purpose of this stage is to collect as much as possible sand in the reclamation site. In this stage, usually the sand can easily washed out from the reclamation site. That’s why in this step, a temporary structure need to be construct in the perimeter of reclamation boundary. This step done until the sand needed up to the planned level. After that the sand need to be compacted and re leveling (when you do the compaction, the level of sand fill will be decrease).

Compaction and re leveling (source: google.com)

The last stage is the construction of revetment. The revetment consist of several layers, Outer layer (called armour layer) is the main layer to withstand the wave energy. After that there is a filter layer (can be 2 layers, depend on the needs) and underneath there is a core of revetment. If the core of revetment is sand, the geotextile should be placed to cover the core from the filter layer. The geotextile also prevent the sand core wash out to the sea (if this is happen, you just wait your revetment failure).

Cross Section of a revetment and its component (source: google.com)

The most important component of revetment is the toe (in the drawing it’s called apron). If this part failure, the whole revetment will be failure. (In another chance I will try to make article about this)

Ok, back to the construction method. Geotextile laying can be done effectively by rolling down the rolled and sewed geotextile from top of the slope down to toe of the revetment (look at next figure). In wet part, the weighting material may be needed.

Geotextile installation (source: google.com)

After that, the stone can be placing on top of the geotextile, the filter layer is first and then the armour layer. A good positioning and placing control system is essential for this work to achieve the required design level. It should be noted that a random placing is better for the stability and over topping rather than a smooth one. It is because, when we put it randomly, the wave will be absorb well and the energy of the wave will reduce, that’s why the wave will have lack energy to run up the top of revetment (result in reducing  the amount of water inundate the area behind the revetment).

 Revetment Construction (source: google.com)

After all, the reclamation is ready to be presented J  

It should be noted that a good design will be useless if the construction not perform well and indeed, a bad design never gave a good result.

Ok guys, I think that’s all.. I hope you can gain something from this article.

Feel free to comment (cause I love to learn) and to ask (so both of us can learn)..

Cheers J