Research predicts Ganga Basin will face more floods, landslides in near future

 Researchers from the Indian Institute of Science (IISc) and the Indian Institute of Technology, Kanpur (IIT), have published a study in Scientific Reports that provides insight on how climate change and anthropogenic activities such as dam building, changes in land cover, and surface as well as groundwater removal have all affected the region. The data for the study spans decades, from 1971 to 2010. The study splits the data into two periods, pre-1995 and post-1995. The effect of human activity in the region was studied on two major tributaries of the Ganga, Alaknanda and Bhagirati, which converge at Devprayag to form the Ganga. 

Weather stations located along the rivers provided the necessary information for the study, which included data on rainfall, water discharge and sediment flow. The researchers found that post 1995, there was a striking increase in flooding events in the river basins of both Alaknanda and Bhagirati. Due to the anthropogenic activities, the rivers does not behave like they are expected to. The courses have changed and the Ganga is extremely polluted. There has also been an increase in the number of catastrophic landslides in the region. The Manheri, Tehri and Koteshwar dams on the Bhagirati have led to changes in the flow levels on the river. From 1995 to 2005, the Alaknanda Basin saw a doubling of water flow at the Joshimath weather station. 

The region covered by the study. The triangles represent dams, while the greren circles are the weather stations. (Image credit: Swarnkar, Mujumdar, Sinha / Scientific Reports)

The research suggests that after 2010, the building of dams along the Alaknanada might have modified the water activity in addition to the climatic changes. Somil Swarnkar, a postdoctoral fellow at the Interdisciplinary Centre for Water Research (ICWaR), IISc, and first author of the study says, "We observed that Alaknanda Basin has a high, statistically increasing rainfall trend, unlike the Bhagirathi Basin. Most of these trends were observed in the downstream region of the Alaknanda. Therefore, we have also seen an increase in the magnitude of extreme flow in these regions." 

The large scale hydraulic projects in the region, including dams and reservoirs have influenced the sediment transported by the rivers. Sediment depositions in the upper reaches of the Ganga have led to changes in the sediment composition downstream because of abrupt changes in the water flow. In the upper Ganga Basin (UGB), the Tehri dam plays a crucial role according to the report. The large reservoir and flow control structure blocks sediment flow from upstream, and controls the volume of water that flows downstream. 

There are 11 new dam projects planned for the Bhagirati Basin, and 16 in the Alaknanda Basin, which are likely to affect the water flow and sediment transport process in the region. The study predicts an increase in the number of extreme flows and the occurrences of floods in the Ganga Basin. However, using computer modelling to drive the decision making combined with informed planning can help reduce the number of devastating floods. Pradeep Mujumdar, corresponding author of the paper explains, "We do not have control over what happens in the atmosphere. But on the ground, we have control. Flows can be predicted using hydrological models. With this knowledge, we can develop both structural and non-structural responses to mitigate such high flows." 

There is a significant variability of the magnitude and frequency of rainfall because of changing hydrometeorological conditions across the globe. There are a number of potential causes for an increasing amount of rainfall in the region, and is an active area of research both locally and globally. Mujumdar says, "We looked at the high-intensity rainfall trends in the Bhagirathi and the Alaknanda river basins. The exact cause of increased rainfall in the region is difficult to pinpoint at this stage: climatic factors could be the primary cause, but increased moisture from surrounding regions because of human activities could also be another reason. The factors influencing the extreme rainfall trends in these river basins are at present being pursued through active research by various teams in the country. It may also be noted that attributing a single cause to extreme events is very difficult and science is being developed globally towards addressing this issue" 

The exact causes of the increased landslides were not part of the study, and is a totally different area of research. Mujumdar explains, "In this work, we are primarily focused on the hydrology of the UGB. The issues related to landslides are not covered in this work. That is a different area of research altogether." 

Scientific modelling and computation can go a long way in predicting and reducing the extreme flow events. Mujumdar says, "Scientific modelling of floods would help us to quantify the aerial extent of likely inundation in the UGB and the increasing risk of flooding. Coupling numerical weather prediction models with hydrologic models has been attempted with promising results to identify the problems. Once the problems are identified fairly accurately, engineering (eg, enhancing the structural infrastructure capability) and non-engineering (for example, low impact development measures and optimal reservoir operation) solutions may be readily developed." 

Planned hydraulic projects in the UGB. (Image credit: Somil Swarnkar, Pradeep Mujumdar and Rajiv Sinha / Scientific Reports)

Advances in technology and the development of new large scale hydraulic structures can also mitigate some of the problems. The Pashulok barrage at Rishikesh for example, has helped prevent floods and reduce extreme flow events downstream. Although the large scale hydraulic projects disrupt the flows in the rivers, they can provide much needed hydroelectric power to the region. Careful management of the dams and reservoirs can actually be used to reduce the number of floods and extreme flows. 

We asked the authors if better management of the hydraulic projects can actually help mitigate some of the disastrous consequences of global warming. Mujumdar tells us, "Yes, the large dams do help in providing water security, hydropower production and in flood mitigation, but then must be managed efficiently. Scientific methodologies and technologies exist now for better management of water infrastructure to offset the impacts of climate change." 

The Ganga is considered as the lifeline of the country, with over 70 percent of the population depending on rivers for sourcing fresh water. Extreme weather events, floods and landslides tend to disproportionately affect communities from lower socioeconomic backgrounds. The findings of this study can help inform sustainable river basin management, and encourage more serious work towards hydrology, ecology and geomorphy in the UGB.