Reviving the Ganges Water Machine: potential

Abstract

Abstract. The Ganges River basin faces severe water challenges related to a mismatch between supply and demand. Although the basin has abundant surface water and groundwater resources, the seasonal monsoon causes a mismatch between supply and demand as well as flooding. Water availability and flood potential is high during the 3-4 months (June-September) of the monsoon season. Yet, the highest demands occur during the 8-9 months (October-May) of the non-monsoon period. Addressing this mismatch, which is likely to increase with increasing demand, requires substantial additional storage for both flood reduction and improvements in water supply. Due to hydrogeological, environmental, and social constraints, expansion of surface storage in the Ganges River basin is problematic. A range of interventions that focus more on the use of subsurface storage (SSS), and on the acceleration of surface-subsurface water exchange, has long been known as the Ganges Water Machine (GWM). The approach of the GWM for providing such SSS is through additional pumping and depleting of the groundwater resources prior to the onset of the monsoon season and recharging the SSS through monsoon surface runoff. An important condition for creating such SSS is the degree of unmet water demand. The paper shows that the potential unmet water demand ranging from 59 to 124 Bm 3 year −1 exists under two different irrigation water use scenarios: (i) to increase irrigation in the Rabi (November-March) and hot weather (AprilMay) seasons in India, and the Aman (July-November) and Boro (December-May) seasons in Bangladesh, to the entire irrigable area, and (ii) to provide irrigation to Rabi and the hot weather season in India and the Aman and Boro seasons in Bangladesh to the entire cropped area. However, the potential for realizing the unmet irrigation demand is high only in 7 sub-basins in the northern and eastern parts, is moderate to low in 11 sub-basins in the middle, and has little or no potential in 4 sub-basins in the western part of the Ganges basin. Overall, a revived GWM plan has the potential to meet 45-84 Bm 3 year −1 of unmet water demand.

Isolating the impacts of anthropogenic water use within the hydrological regime of north India

“…This demonstrates the role that surface water infiltration could play in maintaining irrigation water supply through managed aquifer recharge, a process explored or practiced in many regions – for example, India, the United States and historically as a small‐scale intervention in pre‐Inca infiltration structures in the tropical Andes (Shah, ; Massuel et al, ; Scanlon et al, ; Ochoa‐Tocachi et al, ). Managing aquifer recharge and discharge is a concept central to the Ganges Water Machine (GWM) (Revelle and Lakshminarayana, ; Khan et al, ; Amarasinghe et al, ). The GWM involves drawing down groundwater levels through increased pumping prior to the onset of the monsoon when aquifers will be recharged.…”

Reviving the “Ganges Water Machine”: where and how much?

“…The groundwater pumped is assumed to be consumptive use for ET and hence is lost from the system. In Amarasinghe et al (2016), scenario 2 of unmet agriculture water demand indicated that the agricultural areas in the Ramganga sub-basin could be increased by another 160 000 ha. Thus for this analysis we only consider scenario 2 (from Amarasinghe et al, 2016) of the unmet agriculture water demand.…”

“…In Amarasinghe et al (2016), scenario 2 of unmet agriculture water demand indicated that the agricultural areas in the Ramganga sub-basin could be increased by another 160 000 ha. Thus for this analysis we only consider scenario 2 (from Amarasinghe et al, 2016) of the unmet agriculture water demand. We assume that the additional agriculture area will be wheat, as this crop is predominantly grown during the period of November to March.…”

“…4 are significantly higher compared to the surface values presented in Fig. 3. Amarasinghe et al (2016) estimated the unmet agricultural water demand. Two scenarios were considered in the analysis (Table 4).…”

“…ability to actually capture the excess monsoon runoff to recharge that additional space created -naturally (through surface water and groundwater interactions) or artificially (through managed aquifer recharge -MAR). Amarasinghe et al (2016) examined the first condition above and estimated unmet demand throughout the basin under two scenarios of irrigation expansion. The main objective of this paper is to examine the second condition above, i.e., assess the potential availability of runoff and the impact of managed groundwater recharge on the river flow.…”