THE Coastal Zone Management Plan (CZMP) gives setback lines of reservation and restriction based on observed and expected erosion rates. In the CZMP of 1998, and the revision of 2004 now before the cabinet, this setback varies from 35m to 300m depending on the stretch of coast, a release from Lanka Hydraulic Institute said.
The post-tsunami announced buffer zones of 100m on the western coast and 200m on the eastern coast contravene the setbacks given in the CZMP.
However, setback lines based on erosion and on blanket buffer zones do not have scientific basis when looking at Coastal vulnerability in terms of wave propagation (travel) into the coastal hinterland, as made very clear by the tsunami travel distances varying with location.
The post-tsunami surveys reveal that the tsunami wave has travelled upto 1km inland on the west coast and 1 to 2km on the east coast and the erosion of the coast varies 20 to 30m in the both western and eastern coasts. So are we looking at setback lines/buffer zones objectively with sound scientific study?
The Coastal Zone is vulnerable due to wave action and flooding and monsoon waves, storm surges and tsunamis.
The distance waves can travel to inland depends on the near-shore bathymetry (contours/slope of sea bed), existence of rock outcrops, coral reefs, beach rock, slope of the sea shore, coastline and the hinterland, sand dunes and other coastal features.
The Lanka Hydraulic Institute (LHI), consultants in coastal engineering, water resources and urban water, is of the view that in order to scientifically assess the possible inland propagation, detailed data must be obtained near-shore and comprehensive near-shore hydrodynamic modelling should be carried out.
The modelling can be mathematical modelling or physical modelling. However, with the long coastline involved and considering the current state-of-the-art in mathematical modelling, it is logical to carry out mathematical modelling for such an assessment.
Setback lines based on coastal wave propagation vulnerability mapping
Gathering the required data and information and modelling several scenarios will give us logical vulnerability maps based on characteristics of the wave propagation (travel) inland.
Vulnerability can then be classified generally as "low", "medium" or " high" and based on these assessments we can detail setback lines.
However, Sri Lanka has many coastal water bodies - lagoons and estuarine basins. Therefore, it is important that coastal vulnerability is assessed together with Hazards propagating from these coastal water bodies.
This is particularly so in the Eastern Province, with its large lagoons and estuary basins spread over a large tract of the coastline.
We should not move people away from the coastline to areas that may actually be more vulnerable to flooding. Hence, we should look at Coastal Zone Management in combination with river basin water management including estuaries and lagoons.
Twenty five percent of Sri Lanka's population live along the coastline, hence any imposition of setback lines and relocation of the near-coast populace has to be done after a comprehensive but quick scientific, hydrodynamic modelling study of vulnerability.
A vulnerability study based on wave travel and flooding should be the first step in the setting up of an all-hazards warning and management system, the release said.
LHI which maintains a state-of-the-art hydraulics laboratory in Moratuwa is currently engaged in hydraulic studies of the proposed new Colombo South Harbour, feasibility study of the Hambantota Sea port and in the salinity study of the Walawe Ganga.
LHI has capabilities and 20 years of experience in hydrodynamic modelling of near-shore wave propagation and in river hydraulics, both in physical modelling and mathematical modelling, the release added.