Design principles from traditional mountain irrigation systems (bisses) in the Valais, Switzerland

The bisses are a traditional mountain irrigation system constructed in response to periodic water deficit during the summer months in the Valais canton of Switzerland. The origins of the bisse system can be traced back to the 11th century AD, but may be as old as the Iron Age. The system expanded rapidly in the fifteenth century because of economic incentives to intensify meadow production. The design principles, governance, and organization and water management strategies changed little from this period up to the end of the 19(th) century, despite periods of demographic and climatic change. Since this time the bisse system has been modernized and rationalized in line with wider structural changes to the economy and technological advancement. This paper describes some of the fundamental changes to design principles which have occurred to the bisse system during the 20(th) century and assesses the likely impacts these may have on the long term sustainability of bisses. These findings are then discussed in relation to other mountain irrigation systems. The wider relevance of these findings to irrigation planners of the future is also discussed.