Study on operation strategy for a multi-objective off-stream reservoir with large lakebed seepage to enhance climate resilience

Combining flood dams with aquifer recharge may enhance water resource sustainability, flood protection and drought prevention. In an off-stream reservoir with a high seepage rate, some of the stored surface water can infiltrate into the aquifer. The recharged water can later supplement the water released from the reservoir to fulfill the requested water demand. In such cases, optimal reservoir management requires consideration of the leakage losses (aquifer recharge rate). In this study, a methodology, based on the combination of a calibrated numerical groundwater flow model (MODFLOW, Harbaugh et al., 2017) for simulating reservoir-aquifer interaction, and an optimization model, for the reservoir operation management considering surface/groundwater interactions is presented. The groundwater flow model was developed by means of the FREEWAT platform (Rossetto et al., 2018) and used to obtain a leakage function representing the reservoir's leakage loss to the aquifer in response to different water levels in the reservoir. The leakage function is embedded to the reservoir mass balance equation in the optimization model. The optimal policy was derived based on maximizing the reservoir's water yield while considering different constraints such as the water demand and storage constraints. The modeling method proposed in this study was applied to an off-stream artificial lake located atop an alluvial aquifer in the north-east of Iran. The reservoir was built to store the flood flows of the Bar river for water supply for domestic and industrial needs and with the secondary objective to intentionally recharge the aquifer. Based on the results, the distance between the total demand (12 Mm³/year) and optimal release from the reservoir (5.7 Mm³/year) could be largely supplied by groundwater via pumping wells while the aquifer recharge provided by the leakage is 7.26 Mm³/year. This study demonstrates that the possibility to move surface water to aquifers offers an opportunity to better manage water resources, increase water supply reliability and resiliency (Joodavi et al., 2020). Furthermore, the methodology presented can be tailored for application to any reservoir (artificial lake) system, enhancing its operational, planning, and management aspects. This allows for a precise evaluation of the impact of operational policies on lakebed seepage.

References

• Rossetto, R., De Filippis, G., Borsi, I., Foglia, L., Cannata, M., Criollo, R., Vázquez-Suñé, E., 2018. Integrating free and open source tools and distributed modelling codes in GIS environment for data-based groundwater management. Environ. Model. Software 107. https://doi.org/10.1016/j.envsoft.2018.06.007
• Harbaugh AW, Langevin CD, Hughes JD, Niswonger RN, Konikow LF, 2017. MODFLOW-2005 version 1.12.00, the U.S. Geological Survey modular groundwater model: U.S. Geological Survey Software Release, 03 February 2017, http://dx.doi.org/10.5066/F7RF5S7G
• Joodavi A, Izady A, Karbasi Maroof MT, Majidi M, Rossetto R, 2020. Deriving optimal operational policies for off-stream man-made reservoir considering conjunctive use of surface- and groundwater at the Bar dam reservoir (Iran), Journal of Hydrology: Regional Studies. 31, 100725, https://doi.org/10.1016/j.ejrh.2020.100725