The draft CZMP 2019 for Goa has been a bone of contention ever since it was proposed. Several NGOs and panchayats have projected their own plans. The CRZ 2011 does not offer any such provisions; instead, the instrument mandates that CZMP should be prepared according to specific procedures. Also, there is a demand that, in addition to HTL, the hazard line needs to be likewise shown. Lately however, a strange issue of sluice gates has cropped up. Apparently, CRZ rules should not be applied to tidal creeks and backwaters beyond these conduits. Such a bizarre idea neither finds place in CRZ 2011 guidelines nor is it scientifically valid. As such, considering the HTL and the hazard line composite, the following topics merit attention:
Based on CRZ 2011 rules, the HTL is defined as “the line on the land up to which the highest waterline reaches during the spring tide”. The definition of HTL takes into consideration inundation due to maximum tide (spring tide) and also the wave uprush during monsoon choppy seas. The criteria used for HTL mapping include: (A) Vegetation line is the seaward most boundary up to which ‘ipomoea’ creepers advance, mostly in a linear fashion, also marks the base of dunes, and can also be called the dune line. Although the most stable, frontal vegetation may be obscured at places due to footfalls/trampling. (B) Beach berm is a sandy crest from where the beach slopes abruptly sea ward, often considered as HTL. (C) Sea walls or embankments wherever present are the direct indication where marine water can reach, hence the HTL limit. (D) The base of cliffs, promontories or rocky shores marks the maximum reach of sea waves. (E) Wherever dunes are eroded, the foot of the vertical scarp is the HTL. (F) In the case of mangroves, wetlands or marshes the issue of HTL may be slightly complicated due to large horizontal marine transgression.
Similarly, the CRZ 2011 (section 5, iii) and CRZ 2019 guidelines for CZMP (Annexure IV, part 2) mentions that a ‘hazard line’ has been demarcated by the Survey of India (SOI) taking into account the extent of the flooding on the land area due to water level fluctuations, sea level rise and shoreline changes (erosion or accretion) occurring over a period of time. Delineation of hazard line is based on two components: (a) the coastal inundation levels (flood line) due to natural phenomena such as tides, storm surges and cyclones, estimated from existing tide gauze data, and (b) the rate of coastal displacement (erosion line), computed from recent satellite data and topo-sheets. Once the flood and erosion lines for given time intervals have been mapped, a composite line will be drawn based on more landward of the two lines. This composite line known as ‘Hazard Line’ will represent the worst-case potential natural hazard.
What could be the repercussion of a hazard line along the open beaches, cliffs, rivers and backwaters of Goa? Will it be beneficial or detrimental for frontal sandy beaches and interior wetlands? Open ocean sandy beaches of Goa are governed by daily tides, sea waves, littoral currents, monsoon wind-induced wave run-up, and abnormal waves due to occasional cyclonic activity. These dynamics often erode sand from beaches, dune faces in particular, as observed in Benaulim on 02 November 2019. It is safe to state that sandy beaches of Goa are by and large stable, affected only by annual cyclic erosion. The same parameters apply to all sea cliffs and promontories, morphological features which are relatively stable. Therefore, the erosion line, the flood line, and the resultant composite hazard line on open coasts will be close to or slightly landward of the HTL.
In comparison, the hazard line along river banks, creeks, backwaters and wetlands or khazans is rather complicated. Consider the low-lying khazans of Quelossim – Borim – Rachol – Macazana stretch along the Zuari river; the widest khazan is located at Raia – Ambora. Here, the river is some 350 metres wide, and hence the applicable setback (NDZ) is 100 metres from HTL (river bank). However, by virtue of the extensive low wetlands criss-crossed by saline creeks and backwaters, the entire area is highly vulnerable to flooding. As such, in this case, the hazard line will extend as far as Ambora, a distance of 1.4 kilometres. Consequently, in this flood prone area, the operative width of NDZ will be more than 14 times the normal NDZ.
Similarly, the wetlands of Baga will entirely come under the ambit of hazard line. Identical settings at Cavelossim – Mobor – Assolna around river Sal constitute vast stretches of lowlands, most of which are almost permanently under the influence of marine transgressions. Same criterion applies to wetlands at Paliem, Chopdem, Siolim, Taleigao, Santa Cruz and Merces in the north. Based on a draft hazard map of Goa, it is obvious that all wetland complexes abutting the seven major rivers of Goa will attract protection by virtue of being lowlands highly vulnerable to persistent flooding.
In brief, the concern of potential natural hazards predominantly along low-lying wetlands is the primary reason why the hazard line came about. Compared to HTL, the hazard line is fixed based on an elaborate exercise with multiple oceanographic criteria and needs to be computed. Interestingly, CRZ 2011 and CRZ 2019, under Annexure III (b), reiterate that the proposed constructions shall be beyond the hazard line or 100/200 metres from the HTL, whichever is more. As explained above, the NDZ can thus extend more than 1 kilometre at places. The issue of sluice gates as the CRZ limit will be of no consequence. Being located within wetlands, the entire khazan system of Goa falls within the hazard line, and hence out of bounds for any physical development, except fisheries and agro-activities.
(Dr Antonio Mascarenhas is a former Scientist, NIO, Goa)
