Explanation:

 Ahar-pyne system is an indigenous irrigation technology, which continues to irrigate substantial areas even today in South Bihar plains of India. This system has evolved from an understanding of the particular agro-climatic conditions of the region.
Ahars are reservoirs and consist of a major embankment across the line of the drainage with two side embankments running backwards up to the line of the drainage gradually losing their heights because of the gradient of the surface. Thus, an ahar resembles a rectangular catchment basin with only three embankments, and the fourth side left open for the drainage water to enter the catchment basin following the natural gradient of the country.