Question

why us well irrigation is confined mainly to the Alluvial plains?

Answer 1

In India, with little oil and coal deposits confined to certain parts of the country, ... the Himalayas and associated mountains, the Indo-Gangetic alluvial plains and the Thar desert.

Answer 2

Irrigation is possible and well suited for places with little rainfall.

Alluvial plains also support irrigation due to the fact that .as rivers flow from the mountains with high speed ,it carries sediments that are then deposited in the plains ,the deposited soil is fertile and suitable for irrigation farming .

Alluvial fans contains considerable ground water that replenishes every rainny season ,this makes it possible to do irrigation even when water levels in rivers have gone down