HTL and LTL demarcation: the line every CRZ setback is measured from.

Under the CRZ Notification 2019 the High Tide Line is the line on the land up to which the highest high tide reaches at spring tides. It is the reference datum for the coastal regulation zone: the landward CRZ on the seafront and every setback within it are measured from it.

On the seafront, 500 metres landward from the High Tide Line. Along tidal influenced water bodies such as creeks, backwaters and estuaries, the CRZ Notification 2019 applies a narrower landward width. The seaward extent is covered by CRZ-IV, running from the Low Tide Line into the territorial waters.

The notification provides for demarcation by agencies authorised by the MoEF&CC for the purpose. A demarcation from a source outside that list carries no standing in the clearance process, so the agency should be confirmed before the survey is commissioned rather than after the report is in hand.

Because everything is measured from it. Shifting the line a few metres shifts the entire No Development Zone and every setback with it, which can make a proposed structure appear permissible when it is not, or sterilise buildable land unnecessarily. The error is not local to the line; it propagates across the whole layout.

The HTL is a tidal datum from which CRZ boundaries are measured. The hazard line is a separate line mapped on the basis of erosion, sea level rise and flooding, used for disaster management and adaptation planning rather than as a regulatory setback in itself. Both may appear on a coastal map and they serve different purposes.

The physical shoreline changes through erosion and accretion, and demarcation is carried out against the position established by the authorised agency using the prescribed method. A demarcation carried over from an old drawing without verification is a common weakness, particularly on stretches where the shoreline is known to be dynamic.

If the project falls within the coastal regulation zone, the applicable setback has to be measured from a demarcated HTL regardless of project size. Small projects are in fact where the line matters most, because a modest setback error is enough to place the entire footprint inside a No Development Zone.