Changes in groundwater levels by introducing the canal system in the basaltic aquifer of Narmada basin, Central India

One of the major concerns for agriculturally driven countries like India is said to be the depletion of groundwater. Therefore, understanding the dynamics of groundwater system is prerequisite for assuring its sustainability. According to the GRACE (Gravity Recovery and Climate Experiment) satellite data, the declining TWS (terrestrial water storage) trends are apparent in north and south of India during 2003-2016, while the Narmada river basin, which is situated in the central west of the country, shows apparent increase of TWS. To unravel the possible reasons for this increasing trend, the part of the Narmada river basin was studied. Between 2003 and 2016, two dams (Indira Sagar dam (2005) and Omkareshwar dam (2008)) were constructed in the basin, and the canal systems to supply water for agricultural activities were developed. The canal system was considered to influence water resources availability in the area, and hence, groundwater fluctuations and groundwater storage. To understand the impact of the canal system on groundwater behavior, the well water levels were analyzed based on two timelines, i.e., before (1996-2010) and after the canal operation (2011-2017) in the Omkareshwar canal command area. The wells were classified into three groups, i.e., those located nearby the canal network, nearby the river network, and outside the canal command area. Pre-monsoon (dry) and monsoon (wet) seasons were chosen for the analysis. The results indicated that, after the canal operation, only the wells located nearby the canal showed the average well water level increase with about 2.56 m in pre-monsoon and 1.97 m in monsoon season, respectively. Whereas, the wells located nearby the river network showed very small changes, i.e., about 0.53 m drop in pre-monsoon and 0.84 m drop in monsoon season, respectively. Similarly, the wells outside the canal command area showed only 0.18 m drop in pre-monsoon and about 0.42 m increase in monsoon season. In summary, the groundwater well levels were observed to increase in wells located near canal system, after the canal operation, in both pre-monsoon and monsoon seasons with a considerable water depth of approximately 2 m. These distinct differences observed in the well water level changes indicated that the Omkareshwar canal system has been influential to the groundwater storage in the study area, and this may at least partly explain the reason why the terrestrial water storage has increased in this area.