Decaying delta
THE Indus delta, once a pristine ecosystem, has lost its glory. Listed amongst the 40 most biologically rich ecoregions in the world, it is also a Ramsar site. Unfortunately, its mangrove forests and fish stock in its estuaries are dwindling and communities are abandoning their abodes due to scarce livelihood resources. Abject poverty, food insecurity and morbidity are rampant. The prosperous past of the area has given way to deprivation over the decades.
Commissioned in 1932, Sukkur Barrage was the first major diversion structure on the Indus river. The last century witnessed a series of dams and barrages being built on the Indus and its tributaries. The Tarbela and Chashma reservoirs on the Indus and Mangla Dam on the Jhelum river are the major storage sites. Since the Sutlej Valley project (1922-30), the rivers of the Indus basin have become entangled with three major dams, 23 barrages, 12 inter-river canals and 45 main canals. This web of canals has sprawled a massive irrigation system that has drastically curtailed flows to the delta area.
The massive upstream diversion that continued over a century has culminated in an ecological disaster in the Indus delta. The Indus delta was spread over an area of 600,000 hectares between Sir Creek to the east and Phitti Creek to the west. It had 17 active creeks, which have now shrunk to just two — Khobar and Khar.
Declined river flows have had a detrimental effect on the delta.
According to Census 2023, three deltaic districts of Sindh (Thatta, Sujawal and Badin) have eight talukas with a population of about two million people. This population is directly affected by the degradation of the delta. Declining fish catch, degraded farmland, increased frequency of cyclones and the malfunctioning Left Bank Outfall Drain have together aggravated poverty, unemployment, malnourishment and migration to other areas.
The declined river flow has had a detrimental effect on the delta. It has curtailed sediment transportation, which is a critical ingredient of the deltaic ecosystem. The silt forms the bed that hinders sea encroachment along its shoreline and also provides fertile soil to grow and sustain the mangrove forests. The mangroves are a breeding ground for several species of fish. The flow data of the last 25 years shows that for 12 years, flows below Kotri Barrage were less than 10 million acre feet (MAF) that was provisionally agreed on in the inter-provincial Water Apportionment Accord of 1991. Consequently, sediment transport to the delta has declined. The Indus delta would receive 400 million tonnes of silt in the pre-Tarbela years, which has declined to about 125Mt per year.
According to a report by the International Panel of Experts, 5,000 cusecs is the minimum flow required below Kotri Barrage to sustain the deltaic ecosystem. However, water flow data reveals that except for the two monsoon months (mid-July to mid-September), the desired quantum of water doesn’t cross the gates of Kotri Barrage. In other words, no silt reaches the coastline for most of the months, paving the way for sea intrusion.
In 2001, the government of Sindh estimated that up to 0.5 million hectares of fertile land in the coastal districts (12 per cent of the total cultivated area in the entire province) was affected by seawater intrusion. The report of the International Panel of Experts in 2005 mentioned that coastal accretion was about 30 metres every year.
A research paper by Dr Altaf Ali Siyal of the US-Pakistan Centre for Advanced Studies in Water mentions that the active delta occupied an area of about 13,900 square kilometres in 1833, which has shrunk to 1,067 sq km, marking a colossal reduction of about 92pc. In 2005, the IUCN reported the area of the active delta as 1,190 sq km. A fresh survey through satellite technology is required to determine the quantum of precious land lost to the sea. The panel of experts recommended that a total volume of 25 MAF every five years should be released to transport the requisite amount of silt.
The research revealed that an area covered with mangrove forests comprised 103,413 hectares or 16pc of the tidal floodplains during 1990, which slowly decreased to 63,296 hectares or 9.81pc of the tidal floodplains in 2005. Recently, the provincial government made efforts to revive the mangrove ecosystem. Its efforts saw an increase in the mangrove cover to 81,324 hectares in 2017. Sustaining the mangrove cover requires regular freshwater flows to the estuaries.
Amid this devastation of a fragile ecosystem, constructing new canals upstream for corporate farming will further suffocate the delta, which is a national asset. The delta’s resuscitation is a national obligation. A moratorium on new upstream diversions is urgently needed for the Indus delta to survive.
The writer is a civil society professional.
Published in Dawn, December 21st, 2024