Generalising figures of water uses, productivity or irrigation efficiency for surface irrigation systems it has been a normal quote by many water specialists, which in many cases leads to erroneous conclusion with regards to water allocation and management. While most of large and improved water righted schemes in Tanzania are managed conventionally (i.e. at prior known water requirement per area), most of traditional irrigation systems do not operate in a similar fashion. The available water and ability of farmers to trickle water from one field to another to as far as possible define the area of most traditional systems. This document summarises a comparative study on paddy water use and productivity of three farms arranged serially from the headwork (Top, Middle and End) in a way allowing water reuse between the three farms/schemes. The top scheme was modern followed by an improved scheme while the traditional scheme was positioned at the tail end. While the competition of water was observed to be relatively higher as you go downstream, the decrease in annual volumetric water use in fields as you go downstream was also apparent.
Report for RIPARWIN Project, DFID-KAR Project No. R8064, Soil-Water Management Research Group, Sokoine University of Agriculture, Tanzania, pp 34
Irrigation Productivity Paradigms.