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Abstract
The paper aims to investigate the economies of scale of Water Users’ Associations (WUA) in
Tunisia. During the last years there has been a lot of discussion in Tunisia about the optimal size
of WUAs, which allows more efficient management of the water resources at the local level. In
this work we propose to see if the size of the WUA in the governorate of Nabeul (Central-Eastern
part of Tunisia) would have to increase or decrease in order to maximize their efficiency. Apart
from this qualification we also quantify the scale efficiency and scale elasticity of the WUA using
Data Envelopment Analysis (DEA) models. The results show that the output space (volume of
water distributed and number of ha managed and irrigated) of the WUA that attain a high level of
scale efficiency is highly diverse, indicating that the number of ha irrigated and the volume of
water distributed are not explaining the differences in the scale efficiency of WUA. The
calculation of scale elasticity of the WUA shows that 41% of the WUA are operating at
decreasing returns to scale (DRS) while 16% and 43% operate at constant (CRS) and increasing
(IRS) returns to scale, respectively. The scale orientation was found to be depending on the
output density rather than on the output size. Thus, WUA located in more irrigation-intensified
areas were found to be IRS oriented. WUA operating at CRS were found to have the minimum
costs, which is in line with the theoretical predictions that suggest that the average productivity is
maximized when the scale efficiency is equal to 1.