Indo-Gangetic Fluvial System
The structure and dynamics of groundwater systems in northwestern India (2013-2016)
India, the largest agricultural user of groundwater in the world, has seen a revolutionary shift from large-scale surface water management to widespread groundwater abstraction in the last 40 years, particularly in the northwestern states of Punjab, Haryana and Rajasthan. As a result, these states are now a hotspot of groundwater depletion, with 'the largest rate of groundwater loss in any comparable-sized region on Earth' (Rodell et al., 2009; Tiwari et al., 2009). This unsustainable use of groundwater is aggravated by (a) increasing demands from a burgeoning population and industrialization, and (b) poorly understood effects of climate-driven changes in the water cycle.
Despite this pressing need, there is no integrated view of the aquifer system in northwestern India, no detailed understanding of the decline in groundwater levels, and no regional-scale conceptual framework with which to understand these changes and forecast the evolution of the system. Our project sets out to address these major gaps.
Major research questions
- What is the spatial pattern of groundwater depletion in northwestern India?
- What controls the spatial distribution of groundwater aquifers?
- What are the sources and residence times of the groundwater?
- How might the groundwater system respond to future changes in monsoon precipitation?
Approach and methods
- Systematic multi-year analysis of archived water level data across multiple states (Punjab, Haryana, and Rajasthan)
- Geomorphic and subsurface investigations of the aquifer system, aided by resistivity surveys and archived borehole data
- Drilling, coring, and dating to provide a detailed stratigraphic framework of the aquifer system
- Isotopic determination of groundwater ages, sources and dynamics
- Regional-scale modeling of groundwater flow
Our geomorphic and stratigraphic investigations in this region are aimed at documenting how aquifer properties vary across the region, and relating this to the geomorphic setting of each part of the system. This will give us a conceptual or predictive model for aquifer body dimensions and how they vary across the region.
The aquifer system consists of large sedimentary fans deposited by the Sutlej and Yamuna rivers. These fans were built by sandy river channel deposits which radiate outward from the fan heads at the Himalayan mountain front and which form the individual aquifer bodies within this system. These aquifer bodies are limited in both
thickness (1 to ~80 m) and width (1 to 5 km), and cannot be correlated across the entire study area. The channel deposits are separated, laterally and vertically, by silt and clay deposits. Lateral shifts in channel position, termed avulsions, have built up the conical fans over time. While the present-day river channels and the most recent paleochannels are visible at the surface, it is important to realise that similar channel deposits are found everywhere below the fan surfaces, albeit at different depths in different locations.
The fans are separated by an interfan area that has not received sediment from the Sutlej or Yamuna rivers, but has been built up instead by sediments transported from smaller, foothills-fed rivers such as the Ghaggar River. At present, the Ghaggar flows along the boundary between the Sutlej and Yamuna fans, and has re-occupied themost recently abandoned paleochannel of the Sutlej River (termed the Ghaggar-Hakra paleochannel) along part of its length.
We have compiled aquifer thickness data from ~250 CGWB wells that extend to at least 200 m depth. These data show that the overall percentage of aquifer material – that is, the percentage of subsurface material that consists of sand or gravel – is high in the Sutlej and Yamuna fans, but much lower in the interfan area, even close to the Himalayan mountain front, and along the Ghaggar-Hakra palaeochannel. Aquifer bodies are also thicker, on average, in the fans compared to the interfan area and Ghaggar-Hakra palaeochannel.
The low aquifer percentage and thin aquifer bodies in this palaeochannel coincide with the area of greatest water-level decline. Aquifers make up a smaller proportion of the subsurface in the distal fan areas, but their average thickness remains uniform across the study area. These observations provide a way of predicting the proportion and thickness of aquifer bodies, even in areas without existing borehole data.
In summary, the Sutlej and Yamuna fans form the major aquifer systems, and control the thickness and stacking of individual aquifer bodies. These individual bodies are limited in both thickness and width, and are not laterally extensive. This high spatial heterogeneity appears to be related to patterns of groundwater decline, and must be considered in any future aquifer management scheme. We are now developing probabilistic maps of likely palaeochannel position, using existing aquifer thickness data and simple geomorphic rules that govern channel geometry. Such maps can be refined as additional wells are drilled, but provide an initial estimate of the likelihood of finding suitable aquifer material at a given position and depth.
To document the spatial pattern of groundwater loss, we have integrated historical water level data from state groundwater departments of Haryana, Punjab and Rajasthan (2915 wells for the period 1974-2010) together with Central Groundwater Board data from an additional 997 wells (2002-2011).
The greatest decline in groundwater levels occurred within the Ghaggar River basin along the Punjab-Haryana border, with broader areas of loss across central Punjab and Haryana. Many areas show near-stable or gradually declining groundwater levels between 1974 and 1998, but increasing rates of decline beginning in 1998-2000. Preliminary analysis suggests that district-wide patterns of rainfall, abstraction, and tubewell densities do not match these patterns, and so cannot fully explain the observed decline.
To probe further, we are estimating groundwater volume loss during 1974-2011, and carrying out detailed time series analysis using a 10x10 km grid to identify areas that show similar changes in water levels over time, to help understand the causes of groundwater level change.
Changing Water Cycle Program (Ministry of Earth Sciences, New Delhi and National Environmental Research Council, UK)
Indian Partners: Rajiv Sinha, (IIT Kanpur), S.P. Rai (NIH Roorkee), Shashank Shekhar (Delhi University), Dewashish Kumar (NGRI)
UK Partners: Alexander Densmore, Wout van Dijk (Durham University), Sanjeev Gupta, Philippa Mason, Ajit Singh (Imperial College London)
Sinha, R. (2015), Recognizing spatial heterogeneity in aquifer distributions: lessons for sustainable groundwater management, Current Science 109 (3), 395-396 Link
Sinha, R. and Densmore, A.L. (2016), Focus on Sustainable Groundwater Management, Economic & Political Weekly 51 (52), 53-55 , Link
CGWB (2016), Paleochannel of North West India: review and assessment; Report of the expert committee to review available information on palaeochannels Link
Joshi, S. K., Rai, S.P., Sinha, R., Gupta, S., Densmore, A.L., Rawat, Y.S. and Shekhar, S. (2018) Tracing groundwater recharge sources in the northwestern India alluvial aquifer using water isotopes (δ18O, δ2H and 3H). Journal of Hydrology. doi:10.1016/j.jhydrol.2018.02.056