Modeling the impact of water withdrawal schemes on the transport of pesticides in the Kouris dam (Cyprus)

As part of an effort to understand the water quality dynamics in the Kouris Dam and the
impact of possible management strategies, the present study assessed the transport process
of atrazine in this reservoir and the effects of bottom and surface withdrawal schemes. The 2-
D laterally averaged CE-QUAL-W2 model was used in this study. It was found that, during the
period of upstream river discharge, significant vertical variations of atrazine concentrations
could be observed in the epilimnion. The maximum concentrations were found at the depth of
5-8m rather than in the surface in this period. This suggests that the widely used assumption
of complete mixing in the epilimnion is not valid for this period in this reservoir. It was also
found that the dynamics of atrazine in the Kouris Dam were noticeably affected by the
withdrawal schemes. Bottom withdrawal would significantly facilitate the transport of
pesticides in this reservoir and therefore result in noticeably higher pesticide concentrations in
deep layers. However, surface withdrawal is not able to lower atrazine concentrations in the
epilimnion in this reservoir possibly due to the decreased mixing depth corresponding to the
surface withdrawal, although more atrazine would be removed from the reservoir by the
surface withdrawal. These results suggest that it is sensible to integrate withdrawal schemes
into reservoir management system to achieve different water quality objectives under various
scenarios.