According to groundwater experts in CGWB, the groundwater availability in territory is controlled by the “alluvial formation” and quartize hard rocks. The NCT Delhi can be divided into following distinct hydrogeological units:
First newer alluvium — Yamuna flood plain deposits, Older Alluvium — Eastern and western sides of the ridge while second, Older Alluvium — Isolated and nearly closed Chattarpur alluvial basin and Quartzitic Formation — NNE-SSW trending Quartzitic Ridge. The alluvial deposits are of Quaternary age.
“The newer alluvium belongs to recent age and is referred to the sediments deposited in the floodplains of Yamuna River. These sediments range in texture from clay/silt mixed with tiny mica flakes to medium sand and gravel and this type of alluvium in general characterised by absence of Kankar,” said heyderogeologist.
While the older alluvium consists of sediments deposited as a result of past cycles of sedimentation and occurs extensively in the alluvial plains of the territory. “This is comprised of inter bedded, lenticular and inter-fingering deposits of clay, silt and sand ranging in size from very fine to very coarse with occasional gravels. The kankar or secondary carbonates of lime occur with clay/silt deposits and sometimes as compact pans,” said the hydro-engineer.
The older alluvium is predominantly clayey in nature in major parts of territory except the nearly closed alluvial basin of Chattarpur where the alluvial formation is derived from the weathered quartzites rocks, the hydrogeologist explained.