Bengaluru: Contrary to ongoing efforts to recharge the groundwater table across Karnataka, especially in and around Bengaluru region, by filling up lakes and tanks, the annual report on ‘Dynamic Groundwater Resources of Karnataka 2023’ has revealed that natural rainfall results in the highest recharge of groundwater table.
Of 18.9 billion cubic metres (BCM) of recharge observed across Karnataka, the lakes and tanks contributed only 0.5 BCM, while natural rainfall accounted for the highest contribution of 10.3 BCM, according to the report.Among the districts, Belagavi tops with the highest percentage of groundwater recharge, while Bengaluru Urban and Rural districts occupy the last spots.
According to officials at the Ground Water Directorate of Karnataka, groundwater table recharge happens through six methods — rainfall, groundwater irrigation (GWI), canals, tanks-ponds, surface water irrigation (SWI), and water conservation structures (WCS).
Rainfall was the biggest contributor, followed by return flow from SWI and GWI at 4.9 BCM and 2.2 BCM, respectively, the report stated.
Elaborating further on the study, a minor irrigation department official said rainfall data from three different agencies and the availability of water in various waterbodies during 2022 were considered to estimate the recharge rate. “While assessing recharge through lakes and tanks, we normally consider 60% of the water spread area against the number of days the water lasts. However, in Kolar and Chikkaballapur districts, where KC and HN Valley projects are under progress, it was observed that there was 100% availability of water all through the year as they were filled up with treated water,” the official explained.
Recharging of groundwater table by lakes and ponds is measured in terms of metres per hectare per day, which is the overall increase in the groundwater level calculated in terms of the hectares over which the waterbody nearby is spread on a daily basis.
“Among the districts, Belagavi topped the list by recharging 1,25,931.4 metres per hectare per day (ham), followed by Uttara Kannada and Vijayapura. Bengaluru Rural occupied the bottom place for minimum recharge with just 20,676.2 ham. Barring Ballari, Davanagere, Koppal, Mandya, Raichur, Bagalkot, Haveri, Hassan, Ramanagara and Kolar districts, where recharge was largely through SWI due to vast command area, all other districts witnessed the highest recharge through rainfall,” explained another official.
NS Boseraju, minister for minor irrigation, said, “Whenever there is more rainfall, it directly recharges the groundwater through seepage and percolation. But in drought conditions, it is largely lakes and ponds that help recharge groundwater. However, silt and other sedimentation on lakebeds could have prevented the percolation of water. I’ve already directed experts and scientists to analyse and list out the possible obstacles, and suggest measures to increase the rate of groundwater recharge through lakes and ponds.”
Fall in extraction
Amid concern over depleting groundwater table levels, Ground Water Directorate officials have observed that the ‘stage of extraction’ (SOE) of groundwater is on the decline across Karnataka, barring in Chikkaballapur. “SOE is nothing but how much groundwater you utilize with respect to the recharge. While the SOE was 69.9% in 2022, the same has come down to 66.3% in 2023. Similarly, in Kolar, it was 181% in 2022 and was down to 172% in 2023. However, in Chikkaballapur, the extraction has increased from 146% to 153%,” an engineer explained.
Of 18.9 billion cubic metres (BCM) of recharge observed across Karnataka, the lakes and tanks contributed only 0.5 BCM, while natural rainfall accounted for the highest contribution of 10.3 BCM, according to the report.Among the districts, Belagavi tops with the highest percentage of groundwater recharge, while Bengaluru Urban and Rural districts occupy the last spots.
According to officials at the Ground Water Directorate of Karnataka, groundwater table recharge happens through six methods — rainfall, groundwater irrigation (GWI), canals, tanks-ponds, surface water irrigation (SWI), and water conservation structures (WCS).
Rainfall was the biggest contributor, followed by return flow from SWI and GWI at 4.9 BCM and 2.2 BCM, respectively, the report stated.
Elaborating further on the study, a minor irrigation department official said rainfall data from three different agencies and the availability of water in various waterbodies during 2022 were considered to estimate the recharge rate. “While assessing recharge through lakes and tanks, we normally consider 60% of the water spread area against the number of days the water lasts. However, in Kolar and Chikkaballapur districts, where KC and HN Valley projects are under progress, it was observed that there was 100% availability of water all through the year as they were filled up with treated water,” the official explained.
Recharging of groundwater table by lakes and ponds is measured in terms of metres per hectare per day, which is the overall increase in the groundwater level calculated in terms of the hectares over which the waterbody nearby is spread on a daily basis.
“Among the districts, Belagavi topped the list by recharging 1,25,931.4 metres per hectare per day (ham), followed by Uttara Kannada and Vijayapura. Bengaluru Rural occupied the bottom place for minimum recharge with just 20,676.2 ham. Barring Ballari, Davanagere, Koppal, Mandya, Raichur, Bagalkot, Haveri, Hassan, Ramanagara and Kolar districts, where recharge was largely through SWI due to vast command area, all other districts witnessed the highest recharge through rainfall,” explained another official.
NS Boseraju, minister for minor irrigation, said, “Whenever there is more rainfall, it directly recharges the groundwater through seepage and percolation. But in drought conditions, it is largely lakes and ponds that help recharge groundwater. However, silt and other sedimentation on lakebeds could have prevented the percolation of water. I’ve already directed experts and scientists to analyse and list out the possible obstacles, and suggest measures to increase the rate of groundwater recharge through lakes and ponds.”
Fall in extraction
Amid concern over depleting groundwater table levels, Ground Water Directorate officials have observed that the ‘stage of extraction’ (SOE) of groundwater is on the decline across Karnataka, barring in Chikkaballapur. “SOE is nothing but how much groundwater you utilize with respect to the recharge. While the SOE was 69.9% in 2022, the same has come down to 66.3% in 2023. Similarly, in Kolar, it was 181% in 2022 and was down to 172% in 2023. However, in Chikkaballapur, the extraction has increased from 146% to 153%,” an engineer explained.