Scientists and engineers are about to begin the monumental task of mapping the vast stretch of the Ganges river that runs through India in unprecedented detail. They hope to get started on the work before the monsoon brings bad weather that could delay the project.

Their goal is to create the most comprehensive picture yet of the topography of the river and the human settlements that surround it, to track sources of waste and help authorities clean up one of the world’s most polluted waterways.

“It’s a race against time,” says Girish Kumar, who heads the national surveying agency, the Survey of India in Dehradun in the Himalayan foothills, which is leading the project.

Although the mapping is expected to take about eight months, the team is eager to get started in case the monsoon season, which began in June, forces them to ground the planes that will be doing much of the work.

A fleet of small aircraft equipped with lidar instruments will soon start scanning — one metre at a time — the 2,525-kilometre stretch of river that passes through five Indian states. Lidar is a technique similar to radar, in which instruments bounce laser pulses off the ground. The researchers will use it to produce digital elevation models of the watercourse and the hundreds of thousands of buildings that sit up to 10 kilometres either side of the riverbank.

If the schedule goes to plan, the 3D maps should be available by the end of next year.

Pinpointing pollution

The project will also produce high-resolution maps of the drainage systems of major cities along the Ganges — the network of drains that release sewage and commercial waste water into the river. An estimated 600 million people live in the Ganges basin, and rely on water from the river for drinking and bathing. The Ganges is sacred to the country's large Hindu population, who view the river as a personification of the goddess Ganga and use its waters in religious rituals.

Although some sources of waste in the Ganges are well known, detailed models of how pollution enters and moves along the river will enable officials to design more-effective reduction strategies. Environmental engineer Vinod Tare of the Indian Institute of Technology in Kanpur says that many current government interventions, such as diverting raw industrial sewage away from the river, are implemented without sufficient information to assess whether they are working. “Right now, we do not even have a simple topography of the basin,” says Tare, who has been involved in Ganges-management research for more than three decades.

Government officials also hope to use the maps to improve understanding of how cities develop along the riverbank, and of how the bank is being eroded. This will help local governments to manage risks such as floods. “We will have a better idea of what industries and human settlements will be most affected,” says Kumar.

The mapping project will cost 870 million rupees (US$12.7 million). “It is expensive, but compared to what we will be spending to address the pollution problem, it is hardly anything,” says Tare.

Data access

But water-quality researcher Abed Hossain says the benefits of detailed monitoring will go unrealized if researchers cannot access all the information and use it to develop models and interventions. If the mapping doesn’t go as planned, the government could become worried about negative publicity and restrict access to some of the raw data, says Hossain, who works at the Bangladesh University of Engineering and Technology in Dhaka and is an expert in river remediation. In south Asia, he says, “governments are edgy about failures”. Hossain hopes that independent academic institutions will be granted full access to the results of the survey.

Kumar says that the government has issued guidelines for data sharing and will share the information collected for the project.

The mapping (see ‘Mapping Mother Ganges’) is part of the Indian government’s renewed push to use technology to monitor and clean the Ganges. In 2015, the government approved the 200-billion-rupee National Mission for Clean Ganga, a wide-ranging effort to improve the treatment of sewage, reduce pollution from industry and address the lack of sanitation and toilets in rural areas, which results in human excrement entering the river. The government also promised to build crematoria to deter water burials, in which dead bodies are disposed of in the river.

But as the deadline of 2020 approaches, the government is still a long way from meeting many of its targets. Last year, the country’s independent auditor-general released a report that found that the clean-up effort had been delayed by financial mismanagement and poor planning and implementation.

Numerous studies have also confirmed that the Ganges’ water remains unfit for human consumption or bathing. A major report by the Central Pollution Control Board in 2013 found that a large stretch of the river’s main stream, from Kanpur in the northern state of Uttarakhand to Diamond Harbour near the river’s mouth, cannot safely be used without treatment.

The management of the river is shaping up to be a central issue in the lead up to the general election next year. Kumar says that the maps will be a crucial resource for future interventions. “Before planning anything, we need a map,” he says.