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Tsunami Impact: Summary of Yala Block I Survey

The impact zone of the tsunami was mapped in Yala Block I from Palatupana to Menik Ganga. The coastal zone mapped was approximately 16 km in extent.

Much of the coastal zone was protected by sand dunes over 8 m in height. Wave incursion occurred where there was a break in the dunes as in the case of a lagoon-outlet or a beach with low dunes or where dunes were absent.

The total area inundated by sea water (including the beach) was 7.9 km2. A total of nine areas of major inundation and three of minor incursions were identified.

Areas of major incursions
Yala Safari

Minor incursions
Between Buttuwa & Gona-Lahaba
Behind Yala Army camp
Debaragas-Wala inlet

Water Bodies
A number of fresh water bodies were effected to some degree.

Fresh water bodies inundated:
Patanangala Wewa (breached)
Yala Tank

Water came upto, with possible slight spill/splash into:
Mahaseelawa Wewa (near bungalow)
Wilapala Wewa
Debaragas Wala
Uraniya Wewa
Maynet Wewa

The habitats that were impacted were sand dunes, scrub forest, scrub forest on sand, and grasslands.

The impact on vegetation was studied by conducting line transects in all 9 major areas of inundation. The effects on the vegetation were due to three factors:

1. Force of the wave
2. Inundation by salt water
3. Sand deposition

The effects of these factors were studied on three classes of vegetation, grasses and herbs, bushes, and trees. In general grasses and herbs were heavily impacted by salt water inundation, and the impact was not related to distance from the beach. Trees and bushes were impacted by the force of the wave. The impact was indirectly co-related to the distance from the beach.

Sand dune vegetation was impacted where the wave came over low dunes. However the effects were transient and full recovery will take place. All types of vegetation showed recovery and regeneration, except in the case of trees that were completely uprooted.

A few large mammals were found to have been caught in the tsunami but overall suffered minor casualties. Groups such as small mammals, land-snails, reptiles and amphibians are likely to have been heavily impacted. However, given the patchy nature of the area affected and the large population sizes of these groups, the impacts on the species are likely to be minimal.

The changes that occurred due to the impacts of the tsunami may also benefit some groups:

  • Tangled masses of vegetation may serve as nesting sites for birds or be hiding places for small mammals, reptiles etc.
  • Saline water bodies could be feeding sites for waders

Monitoring use and re-colonization of affected areas would be of interest. Some water bodies are already being re-colonized by frogs.

CCR team
Dr. Prithiviraj Fernando
Manori Gunawardena
H.K. Janaka
L.K.A. Jayasinghe
Jeewanthi Mendis
H.G. Nishantha
Dr. Jennifer Pastorini
Dr. Devaka Weerakoon
Dr. Eric Wikramanayake