Management of Coastal Areas: 4 Ways | Soil Management

The extent of coastal areas is less than 15% of the total area of earth. It accommodates more than 50% of the world population, i.e., about 3.1 billion population within 200 km periphery from the sea. And it is expected to reside about three-quarters of the world population by 2025. The coastal areas contain rich resources to produce goods and services and also creates a kind of shelter to few creators.

In the European Union, about 50% of the population is living within 50 km surroundings of the sea; and contributing a large proportion of economic resource. Changes in sea level creates a direct impact on beaches and coastal systems. On rising of sea level the coastal sediments are pushed back by the high waves. The deposition of sediments at shore bank is called landward sedimentation.

The management of coastal areas is done in following ways: 1. Coastal Protection Structures 2. Beach Nourishment 3. Beach Drainage 4. Monitoring Coastal Zones.

These methods are described as under:

Way # 1. Coastal Protection Structures:

The relevant structures that can be used for coastal protection are given as under:

(i) Groyne:

These are the barriers/walls constructed across the sea waves, using wooden, concrete and/or rock materials. This structure creates a wide and more plentiful beach; and thus enhancing the protection level for the coastal area. This structure filters the sand materials coming along with high waves. And also absorbs the wave energy, which results into reduction of sea bank erosion.

However, there is loss of beach materials on down-drift side. To check this loss another groyne is constructed there. In general, the groynes do not protect the beach against storm-driven waves. And at the same lime, if these are constructed at closure spacing, then there is possibility of creating currents, which carry sand materials, offshore.

Few important features of this structure are mentioned as under:

i. These are extremely cost-effective coastal management measures.

ii. Requires little maintenance.

iii. One of the most common coastal management structures.

iv. Groynes are detrimental to aesthetics of coastline and face strong opposition by coastal communities, sometimes.

v. It is considered as a means to coastal erosion control.

vi. The last groyne or the terminal groyne prevents longshore drift from bringing the materials to other nearby places.

(ii) Sea Walls:

This is another type of sea bank protection structure. Sea walls are probably the second most traditional method used for coastal management. The sea walls are constructed with the help of concrete or rock materials at the base of cliff or at the back of beach. These are also used to protect the bank against erosion or Hooding. The vertical sea walls reflect the wave energy back to the sea.

To make better effectiveness, this structure is also given curved crest walls. This feature increases turbulence, as result there is increase in entrainment of sands and sediments during storm. For selecting the location of sea wall construction, a special care is required to follow regarding swept prism profile of beach, the consequences of long term beach recession and amenity crest level.

Nowadays, the sea walls are constructed using improved design aspects; and these walls are called modern sea walls.

Various features of modern sea walls are outlined as under:

i. Modem seawalls are constructed to dissipate the incident energy of striking waves, and reducing the turbulence. For this purpose these are constructed with sloppy revetments.

ii. In current design, the porous rock or concrete armour with intermediate steps are used for construction. The steps take over the whole of the frontage.

(iii) Revetments:

These are constructed with the help of wooden slanted or upright blockades. Construction is done in parallel array on the coast, towards back of the beach. Its main function is to protect the sea bank against the cliff or settlement beyond. In most common way the revetments are performed using timber slants and rocks for infilling purpose. When strong sea waves strike the revetment, then their KE energy gets dissipated; and also absorbed.

This results into reduction of impacting force on the sea bank; and in this way the bank becomes safe against such type of happening. Because of this action, few beach materials get trap by the revetment. These materials protect the cliff by putting behind the barriers. The revetment may be kept watertight by covering the slope completely; or in porous form to allow the water for filtering after getting dissipation of wave energy.

In normal way, most of the revetments do not interfere with transport of long shore drift. Also, because the wall absorbs the energy instead of reflection, there is erosion which causes into destroying of revetment structure. To avoid this happening the revetments are required to take necessary safety measures.

(iv) Rock Armour:

These structures are built by using large rocks, which are piled/placed at the foot of the dunes or cliffs. The piling should be accompanied with native stones of the beach. This measure is generally used at the erosion prone sea banks.

Working principle of this structure is based on the absorption of wave energy and reducing the level of impacting force of wave; and thus to hold the beach materials against erosion. As demerit, the rock armour has very limited life; and is not effective in storm conditions. Also, there is reduction in recreational value of the beach. Its construction cost depends on the type of rocks to be used for construction.

(v) Gabions:

These are the wire caged boulders/rocks, placed in front of vulnerable face with soil erosion ranging from severe to moderate. Sometimes, these are also placed at the cliff edges or at right angles to the beach like large size groyne. Wire cages are also filled with crushed stones to increase gabions effectiveness. Generally, the hexagonal meshes are more suitable for this purpose, as they have better load distribution than the rectangular meshes.

In its working action, when sea water strikes the gabion, the water gets break: and there is trapping of beach materials along with erosion control. The gabions also cause dissipation of wave energy, which results into checking of sea bank erosion. For maintenance the gabions are securely tied to prevent the wire abrasion likely to be caused by the rocks.

The costs of installation and operation (per meter) of shoreline protection depends on the following parameters:

i. Length of protection required.

ii. Pump flow rates depending on the sand permeability, power costs etc.

iii. Soil conditions, i.e. presence of rock or impermeable strata at the sea bank.

iv. Discharge management/filtered seawater utilization.

v. Drainage system used.

vi. Geographical considerations, i.e. the location logistics.

vii. Consideration of regional economics.

viii. Study requirements/consent process.

(vi) Offshore Break Water:

This is also a kind of structure used for sea shore management. In this method, the big size concrete blocks or natural boulders are sunk to the offshore to alter the wave direction, and also to reduce the wave/tide energy striking the seashore.

In its working action, when strong wave strikes to this structure, then wave energy gets break; and therefore the impacting erosive power of wave gets reduce. This effect leads to development of wide beaches due to deposition of sediments at the sea bank, along with protection of cliff and settlements, behind.

Way # 2. Beach Nourishment:

It is soft engineering technique of coastal management. It involves sand piling on top of existing sand at sea bank. The sand to be used for piling should be of different places, but care should always be taken about quality of the sand. The sand quality should also match with the existing beach materials, so that it can integrate with the natural processes without any adverse effect. The beach nourishment can be done along the groyne. This technique requires a constant maintenance.

Way # 3. Beach Drainage:

It is also called beach dewatering. In this the water table is lowered below the beach face. For this purpose any suitable drainage method can be used. On lowering of water table, the sand becomes well aerated. Also, the beach drainage facilitates to collect the seawater in very pure form, because of sand filtration effect.

This water can be used for following purposes:

i. Discharging back to the sea.

ii. To oxygenate stagnant inland lagoons.

iii. To feed for heat pumps.

iv. To supply for desalination plants.

v. To use for land-based aquaculture, aquarium, seawater, swimming pools etc.

The cost of beach drainage system is considerably lesser than the hard structures.

Way # 4. Monitoring Coastal Zones:

The monitoring of coastal areas is very important. By proper monitoring a lot of properties of the people existing right to the sea bank can be saved. However, one of the major problems regarding this work is the uncertainty in information availability regarding unforeseen events. Probably, the video-based monitoring system is the best to collect the data continuously at low cost; and analyse shoreline processes over a wide range.

The event warning systems (storm warning) can also be used to minimize the impact of catastrophic events causing coastal erosion. Also, the storm surge warning can be used to operate the flood gates; and thus to reduce the bad effects/impacts of such events.