Answer : 4. "Sringaverapura"
Explanation :

1. 1st century BC The water harvesting system that taps the flood waters of the Ganga River was at Shringaverapura, located in the present-day Allahabad district of Uttar Pradesh state of India.

2. The system was composed of three percolation-cum-storage tanks, fed by an 11-meter wide and 5-meter deep canal, which diverted flood water from the monsoon-swollen Ganga.

3. During the reign of Chandragupta Maurya, large-scale dams, irrigation systems and harvesting systems were constructed throughout his kingdom.