Efforts to assess farmer participation in irrigation management have often focused on differences between "large-scale" and "small-scale" systems. There are more obvious possibilities for user involvement in the latter. But "scale" is an ambiguous and difficult variable to use prescriptively. 1 It is more instructive to think in terms of the structure of an irrigation system using the number of levels of operation and organization to delineate patterns of agency and farmer activity in irrigation management. Considerations of structure can tell us much about the complexity and interdependence of the management tasks within an irrigation system.