Coastline behaviour of northern province

 

Coastline behaviour of northern province

 

J.Ketharani

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Department of Civil Engineering,University of Moratuwa.

[email protected]

Supervisors

Mr.A.H.R.Ratnasooriya

Senior lecturer, Department of Civil Engineering,University of Moratuwa.

[email protected]

Dr.T.M.N.Wijaratna

Senior lecturer, Department of Civil Engineering,University of Moratuwa.

[email protected]

 

 

Abstract: Sri-Lanka is an island country consists of 1680km length of coastline. Coastline changes with time because of several human and natural factors, mainly due to soil erosion, and soil mining in Northern Province. This changes cause many adverse effects on fishery, tourism, coastal area residencies, cultivation and ground water. Because of this there is a need for coastline variation analysis. So this research study is conduct about the coastline behaviour of Northern Province through analyzed shoreline variation with time based on the available saterllite images of 20 years. Images get from Google earth PRO as kml file and analysing done with Arc GIS software. Variation of coastline with time will found through this analysis and preccautions proposed to mitigate the changes.

Keywords: Coastline behaviour; Northern coast; Soil erosion; Sediment transport

 

1.    Introduction

There is nothing define as a boundry of coast eventhough coastline is define as the surrounding land part next to the sea; consist of soil, rocks, trees, some other plantations like herbs and other small structures such purposely built with purpose of business and tourism. Changes occuring continuously in the coastlines as it is the dynamic zone of sea and sea waves through erode, transport and deposition of soil materials. This altering action of seashore is to be known as coastline behaviour. It happens because of the various human unfavourable activities and nature acts. Changes in coastline take place with respect to time in short term or long term. Mostly short term changes occur due to mining of soil for constructions, off shores widening, cylones and tsunami. Long term changes occur due to river diversions, monsoons and sediment transport.

Coast lines changes should be analyzed because of it influences sea transport, communication lines, fishing harbour and anchorages, settlements of buildings in surrounding coastal areas, number of tourists attracts, resources in the nearby shore, living of aquatics and other habitants in those areas and industries built at seaside (Kari).

Because of the rapid urbanization and commercial development of harbours are increase the economical importance ofE coastal areas.

Nearly 50-55% of Srilankan shoreline area is subjected to threaten by coastline chaanges (Coastal Erosion). In Srilankan coastlines 40% of coastlines are covered by Northern Province. So casestudy of northern coastline is better even though this part wasn’t subjected to threaten.

2.      Beach profile

Figure 1: Beach profile (A.Kearon, 2014)

Shore is the land environment next to sea and the dynamic boundry between the coast and sea is coastline. According to the location shore is called with different prefixes. Waves dynamic shore is define as near shore and the far part in opposite direction of sea next to near shore called as back shore, sea water remaining in the 5m shore area near to land part is near shore and the 20 m further part of sea after near shore is off shore.

Area where the sea waves begin to breakdown called surf zone.

Any horizontal formation orvertical cut parallel to shore named as berms. It forms by the erosion action of wind or waves.

Dunes are mountainous like structure in a small scale formed with sand. It’s mostly builtup by the heavy or continuous action of wind blowing.

Land part not influenced by the sea but it beyonds the coast then it called coastal hinter land.

3.      Changing factors of coastline

2.1 Sediment transport

Sediment are transported as a result of waving action which mainly induced by wind. Wind pattern assure the transport direction of soil and sediments at coast. It makes longterm changes in coastlines.

Also sediment transport is induced by  unfortunately occuring storms, flood and tsunamis. All these create short term changes in coastlines.

 

Figure 2: Sediment transport.

All these are cause the soil particles movement along the shore , into the sea and off shore. Sediment movement into the sea create negative impact on the land area. It cause erosion in shore and breakdown the shorelines and sea water intrusion starts into the new land area. Sediment movement off to shore builtup shorelines and land area will increase through this. Sediment movement along the shore cause erosion along the sea side (Coastal Erosion, 2002).

3.2  Soil mining

Mostly soil mining is take place with a purpose of using as a material for construction. Soil taking out of surrounding area of sea leads to the intrusion of sea water into the land it may change the ground water quality. When consider about Northern Province ground water is taking for the whole purposes amost drinking, bathing and agriculture. So this may create a big issue. Starting with intrusion, erosion and settlement starts to occur and coastline change begins and continued through mouth enlarging (Sand mining facts).

3.3  Monsoons

In Sri-Lanka, there are four monsoon seasons induce the waving actions in the Indian Ocean.

·         North East monsoon (December-February)

·         First inter monsoon (March-April)

·         South West monsoon (May-September)

·         Second inter monsoon (October-November)

These monsoons are creating pressure differences and it will cause sand blowing in beaches. Due to this soil transported with respect to the monsoon directions. North East monsoon only highly affect the Northern Province coastlines.

3.4  Disasters

Coastline changes occur within short time in case of disasters take place. Tsunami and storms are mostly affect coastline variation disasters.

 Tsunami waves are very huge while comparing with usual waves. These tsunami waves are large waves with high amplitude, high frquency and also high velocity. It has high energy at the time of arrives shore. Respect to the location of Srilanka, only shallow waves are reach our country wih high energy. This is enough to devastate the measurable area. When these waves get into the land it brutally hit the beachside and erode the soil heavily and well change the landshape through transform the coastline with diffraction, refraction, reflection and energy concentration effects of tsunami waves (Hettiarachi & Samarawickrama, 2006).

Waves are mainly eroded by the following actions.

·         Hydraulic action-Hitting of water on the shore with considerable energy

·         Abrasion-bashed against the shore by waves like stones

·         Solution-Dissolved actions with the chemical reactions mainly take place in rocks

·         Attrition-hitting each others and rock shape changes and surface get smooth

·         Compressed air-Air and water trapped between the voids in rocks and tends to expansion in rocks (A.Kearon, 2014)

Normally wind can easily transport considerable amount of soil parrticles. This act is take place in a heavy rate during storms and it can be clearly seen within a short period of time in beach sides. That’s why beaches will subsequently erode at some places and break down or weakening the shorelines and also deposit the soil in different location and builtup coast at that place. Likewise coastline variation depends in storms with respect to its direction, speed and time.

Figure 3: Storm effect in Srilanka (Coastal Erosion)

The tsunami & storms effects are very less in Northern Province while comparing with other provinces in Srilanka.

4.      Earlier reseach attempts

There are several research attempts conduct to analyze the coastline variation depend on the available saterllite images in our country and foreign countries. But in our country this attempt was only done by considerering whole country and especially for some specific areas like south coast. Until now any research wasn’t carried out specifically for North part shoreline variation.

 

 Figure 4: Sri-lankan coastal sectors

These researh analyzes were going in base of setback distances, coastal erosion, existing coast protection measures, natural hazards exposure, availabke free space and developments goingon or  proposed.

Long term changes are observed and identified as whether dynamic or static. If there is any negative or positive movement observed in coastline then itstated as dynamic and it there isn’t a single change observed then it satated as stable.

Several years images of coastlines of Srilanka were taken and it comapared to each other and erosion rate observed in range of 0.5m/year to 12m/year. But during comparing the images difficulties were faced by the shifting of taken images, different zoom levels and less accuracy of images.

Assesments are done based on division of 70 segments (Setback standards for coastal development) which positioned by Coastal Zone management plan. Among those only 24 are vulnerable and proposed coastal protection measure for them, but any north segment is include in it. North parts didn’t have any coast protection structures even though the shorelines are protected by insignificant coastal activity and favourable vegetation on the beach side.

Among the changes of coastlines, almost changes take place at the coastal feeatures like estuaries, lagoons, sandy beaches, marshes, deltas, wet lands and mouths (W.V.K, M.H.G, & S.D, 2013).

In Jaffna peninsula water was contaminated recently. So for this, getting surface water from remote areas is difficult after 70 years due to the seawater intrusion into north part (Sivakumar, 2014). According to this coastline changes in those area results this situation with sand mining. So this intrusion areas are must analyse and studied.

Sediment dynamics along shore is governed by longshore currents generated because of waves and winds of Soth West & North East monsoons.

Figure 5: Longterm conditions of beach due to monsoons (Nalin, Hm, & Indishe, 2016)

5.      Protection measures

In case of heavy change of coastline observed then it should be controlled by providing some mitigation measures. To minimize it following actions can be done.

·         Build coast protection structures at appropriate locations

·         Regulate private constructions at beach sides

·         Limit construction where high amount of erosion encountered

·         Regulate the amount of sand mining with respect to time and location

·         Grow vegetations on the beach sides

·         Drop boulders and rubbles at beaches to slow down waves and reduce erosion

·         Environmental impact assesment for large beach side projects

6.      Conclusion

Coastlines are very important feature of each country. This present research attempt is case study on Northern Province coastlines analyse with respect to avalilabe satellite images of recent 20 years. Analyzing of coastline is necessary for Northern at present as it is tends to developments in coming years. Northern Province has a length of 480km coastline by considereing the coastal area of Jaffna, Jaffna, Mullaithivu, Killinochchi and Mannar (G.A.Chandrasiri, 2009). Especially some small islands are considered as north coastal area. So in these islands more attention have to be pay while analyse the coastline changes.

Coast protection measures are less at north coast side but due to existence of thick vegetation and limited effect of waves. Location is major reason for these tiny effects of variation in coastlines.

 Presently sand dunes built, Coconut tree plantatoins, vegetations, gabion wall built and boulders depsotion can be observed as protection measures. There are more famous beaches located in north. Protection measures in those areas are little high because of the people usage.

After this case study based on image analyse, existing changes can be predicted and if there any vulnerable changes some protection measures to mitigate those variation effects will be proposed according to the major factor influence in those changes.

Acknowledgements

This research project is going on with the guidance and helping of several peoples. So, i would like to convey my gratitude to those peoples at this time. First i like to thank to Mr.A.H.R.Ratnasooriya supervisor and Dr.T.M.N.Wijaratna Co.supervisor of my research. Then i like to thank my colleages who were give hand to me for doing this casestudy in effective manner for the research. Finally i thanked for all who ever help me in any way at any time to continue my project in a successful path.

References
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