‘Thane creek lost 30sqkm in 48 yrs’

Study by mangrove cell reveals area was lost to new mudflats, mangroves; experts say it means high tide along with heavy rain could lead to flooding

MUMBAI: The Thane Creek – a coastal inlet off Mumbai’s eastern waterfront, which separates the city from the Maharashtra mainland – has shrunk by 12% in 48 years, according to an unpublished study by the state forest department’s mangrove cell. The analysis shows that the creek’s water spread area reduced to 202 square kilometres (sqkm) in 2020 from 232 sq km in 1972. About 30 sq km of the waterway has been lost to new mudflats and mangroves.

The study was carried out by the department’s geographic information systems (GIS) specialist, using Landsat satellite images for the years 1972, 1978, 1988, 2000, 2010, 2014 and 2020, and confirms that “there is an overall increase in the spatial extent of mangroves and reduction in the width of the Thane Creek.”

The results are in line with a similar study published by Srushti Conservation Foundation (SCF) and led by Dr Deepak Apte, former director of the Bombay Natural History Society on June 4. Apte’s analysis had shown that the larger Mumbai Metropolitan Region (MMR) has lost 107.6 sq km of waterways and agricultural lands along its coast between 1990 and 2019, as a result of siltation that is likely caused by the deposition of untreated sewage and other waste into the city’s creeks.

The cumulative area lost is larger than Sanjay Gandhi National Park, which is 103 sq km in size. Of this, about 24 sq km of waterway in Thane Creek were lost between 1990 and 2019, Apte’s analysis suggested. Viewed together, results from both the studies indicate that there has been a sharp increase in the rate of siltation in recent years. About 9 sq km of water spread was lost since 2014 at a rate of 1.5 sq km per year, the mangrove cell has shown in their study (an executive summary of which was shared with HT).

The report also notes an increase in the cover of new mangroves, which propagate after taking root in the newly created mudflats. “The mangrove area around Thane Creek has increased from 68.11 sq km in 2014 to 79 sq km in 2020, which is a 10.72 sq km increase in mangrove area in the past six years,” noted the study.

The mangrove cell has said that it will seek the Bombay high court’s permission to uproot these new mangroves, which have grown just before and after the Thane Creek Flamingo Sanctuary was declared in 2015. HT was the first to report on this development on June 5.

“Flamingos and migratory waders are presently benefiting from the shrinking waterways as their population increase is being witnessed in the same trajectory as the expansion of mudflats and mangroves. This in combination with high sewage load that MMR is pumping into the creek as well as warm water from refineries and power plants make it a perfect feeding ground, with nutrient rich flora and fauna,” said Apte.

However, once the accreted land is taken over by mangroves in combination with reduction in tidal prism during non-monsoon months, soft mudflats turn into hard and barren land.

“Thus, flamingos could permanently move away from the area,” Apte added.

Shrinking creeks also mean shallower creeks, which spell bad news for Mumbai at a time when previous studies have indicated a rise in sea levels by 0.5 to 3mm per year in the Arabian Sea, along with of extreme rainfall events in the foreseeable future.

Simply put, shallow creeks cannot hold as much water; so even with a slight increase in sea-level rise and precipitation levels, the combined impact of high-tide and heavy rainfall will lead to a spill-over of water into the city, disrupting the lives and livelihoods of coastal populations and exacerbating degradation of otherwise productive coastal lands.

Published studies, such as the one from January 2020 in the Journal of Coastal Conservation and another by the Salim Ali Centre for Ornithology and Natural History (SACON) and the BN Bandodkar College of Science, Thane, have also noted or demonstrated the siltation issue in Thane Creek.

“Considering the seriousness of this issue where the width of creeks is reducing owing to excess siltation, scientific removal of mangroves will have to be carried out to protect the original coastline,” said Virendra Tiwari, additional principal chief conservator of forests (APCCF), mangrove cell.