G. Zulu et al., CHARACTERISTICS OF WATER REUSE AND ITS EFFECTS ON PADDY IRRIGATION SYSTEM WATER-BALANCE AND THE RICELAND ECOSYSTEM, Agricultural water management, 31(3), 1996, pp. 269-283
Rapid industrial development in the rice-growing regions has increased
competition for the scarce water resources. Water reuse (surface and
subsurface agriculture drainage water, storm runoff, sewerage effluent
and industrial wastewater recycling) is in widespread use as a method
of supplementing the paddy water supply, therefore, there is a need t
o clarify its effects on the paddy system water balance and riceland e
cosystem. Field data and simulation results from a complex runoff mode
l (created on a daily basis), were used to estimate the water balance
and assess the effects on the irrigation system of a water shortage ar
ea in Niigata Prefecture, Japan. For three years (1991-1993), the aver
age water reuse component was within the range 14 similar to 15% of th
e total irrigation water supply. Apart from meeting the water needs at
peak demand periods, water reuse is a quick-response water supply sol
ution during dry spells, increasing both the water reliability and cro
p security. To understand the impact of water reuse on the riceland ec
osystem, its effect on total phosphorus (T-P), total nitrogen (T-N), s
uspended solids (SS), and chemical oxygen demand (GOD) Was assessed. B
lending of the drainage water was done to reduce the irrigation water
concentrations, to approximate the traditional dual canal system and t
o increase farmer satisfaction with the water reuse system. Apart from
the fact that the amount of return flow drained out of the irrigation
system was reduced when drainage water was reused for irrigation, the
effluent load reductions for SS and T-P owing to water reuse were con
sistently high. Hence, water reuse not only helps meet irrigation wate
r needs, but also aids purification of the agricultural drainage water
and preservation of the riceland ecosystem.