This map could make believe that the relief is an essential explanatory factor of the geographical repartition of irrigation, because of the hill range of the Western Ghats located at the east of the State where zones with less irrigation are found. However, the two maps are not superimposed (cf the relief map on the site [www.mapsofindia.com/maps/kerala/keralaphysical.htm]). One sees on the contrary well irrigated zones in the mountains, in particular the Mullaperiyar dam, the water of which is used by Tamil Nadu in spite of the protest of Kerala. In the same way, all the low land is not irrigated, for several reasons: certain places require more drainage than irrigation because of the heavy rains; the use of water can also be restricted on coastal strip by the problems of salinity. In Palghat pass, where there is less rain, irrigation is more important as one could expect, benefitting also from some dams.

A diversity of irrigation techniques is used in Kerala (tank, pound, well, channel, diversion), but one of it is specific and localised in the North of the State: it is called surangam and consists in a horizontal drilling carried out in a mountain foothill until reaching the ground water, such as the famous qanat of the Middle East. The tunnel thus dug can measure up to 300 meters length.

O.A.