Improving Hydraulic Conditions to Preserve Mangroves at Hazira

Abstract

The Forest and Environment Department (FED), Government of Gujarat was concerned about protecting the 22-hectare mangrove patch in the vicinity of causeway approaching Land-Based Drilling Platform (LBDP) of NIKO Resources Ltd (NRL) and behind the reclaimed land of Hazira Port Private Ltd (HPPL), Hazira in Gujarat state. In this regard, the studies were carried out to simulate tidal flow in existing conditions with a culvert of 12 m width at HPPL side and two open pipes of 1 m diameter each at +6 m level on LBDP side. In order to improve the hydraulic conditions in this channel, the studies were carried out by incorporating the 8 m wide culvert at different sill levels on LBDP side using MIKE-21 software. Culvert with sill level at +4.5, +4.0, +3.5 and +2.5 m was incorporated in the computational model, and tidal flow was simulated for each condition. The studies revealed that channel would be hydraulically more active when the sill level of culvert at LBDP side is +2.5 m but it would require dredging of channel up to +2.5 m depth contour beyond LBDP bund on seaside. This area on seaside is prone to siltation and would need regular maintenance dredging which may not be cost-effective. Keeping this in mind, a culvert of width of 8 m with sill level at existing bed level on seaside (i.e. +4.0 m) at LBDP bund has been suggested, which would keep the channel hydraulically active both during spring and neap tides, and at the same time, it would not require dredging of channel beyond LBDP bund on seaside. The existing culvert level on HPPL side which is at +4.5 m is found to be adequate for tidal flow in the channel on port side. Even though the channel would get sufficient water during spring and neap tide, the submergence of Mangroves, which are at +5 to +7 m, would occur only during spring tide. Channels in the mangrove area were also suggested.