Differentiate between Hard-rock and Allu

These aquifers represent around 65% of India’s overall aquifer surface area. Most of them are found in central peninsular India, where land is typically underlain by hard-rock formations. These rocks give rise to a complex and extensive low-storage aquifer system, where in the water level tends to drop very rapidly once the water table falls by more than 2-6 meters. Additionally, these aquifers have poor permeability which limits their recharge through rainfall. This implies that water in these aquifers is non- replenishable and will eventually dry out due to continuous usage.
 
Alluvial aquifers of the Indo-Gangetic plains
These aquifers, found in the Gangetic and Indus plains in Northern India have significant storage spaces, and hence are a valuable source of fresh water supply. However, due to excessive ground water extraction and low recharge rates, these aquifers are at the risk of irreversible overexploitation.