Water resources management in a reservoir-regulated basin: Implications of reservoir network layout on streamflow and hydrologic alteration

Reservoirs have been continuously built in the Poyang Lake Basin (PLB) for the local economy. With pending removal and reconstruction of aging reservoirs and planning of new reservoirs in this area, it is advisable to evaluate the likely impact of the existing and alternative reservoir network layouts on the hydrologic regime for more effective water resources planning and management. In this study, reservoirs of multiple sizes in the PLB were integrated into a coupled land surface-hydrologic model (CLHMS) fully coupled with a reservoir scheme. The extended model was then validated and applied to investigate the impact of existing reservoirs. Seven hypothetical scenarios were additionally set up by removing all the reservoirs, replacing smaller reservoirs with few larger ones, replacing larger reservoirs with many smaller ones, moving all reservoirs downstream or upstream, increasing or decreasing the mean inflow of reservoirs, respectively. In all, eight simulations were conducted and analyzed using the Indictors of Hydrologic Alterations (IHA) for the period of 1981-1999. Results indicate that the existing reservoirs in the PLB are able to effectively displace the excessive streamflow in the wet season to the dry season and mitigate the hydrological extremes. By increasing the mean inflow of reservoirs, the effectiveness of reservoirs in downstream flow regulation can be further enhanced. Similarly, replacing many small reservoirs with a few large ones with a same total capacity can lead to more resiliency against the downstream flow variability and extremes, only if the total mean inflow of the new large reservoirs is not considerably lower than that of the small ones. Relocating reservoirs to a different place with similar mean inflow, however, has a relatively minor and probably case-dependent impact on the hydrologic regime. On the other hand, the ecological analysis on the IHA parameters indicates that the layout preferable for the effective flow regulation may not necessarily be ecologically preferable. In general, this study comprehensively evaluates the hydrological impact of reservoir network layouts, and can provide implications for stakeholders to reach a trade-off between reservoir capacity distribution, locations and mean inflow not only in the PLB but also in different regions worldwide.