Impact of water management policy on flow conditions in wetland areas

This study presents an analysis of the influence of two different water management policies on the natural river ecosystem of the Upper Narew valley. A Global Sensitivity Analysis is used to estimate their impact on water conditions in an important wetland area. The River Narew is modelled using a 1-D flow routing model.The Upper Narew Basin is situated in north-east Poland. A relatively large lowland reservoir, Siemianówka, constructed at the beginning of the 1990s, is situated upstream. The river reach studied is 140 km long with a valuable wetland ecosystem, enclosed within the Narew National Park (NNP), at the downstream end. Previous management plans for the reservoir were focused on direct economic goals, such as energy production, fisheries and land irrigation. However, because of the rapid degradation of the NNP ecosystem observed in recent times, it was decided to include the protection of wetland areas as one of the reservoir’s main goals. To achieve this, the current influence of its release policy on flow conditions is investigated. In addition, this investigation is performed jointly with an analysis of other factors, such as land use changes. Water management activities were represented by the controls having impact on measures, representing the water conditions at the NNP. Their significance was measured using Global Sensitivity Analysis. This allowed each inference/impact in the form of sensitivity indexes to be quantified and compared. Additionally, in the case of spatially distributed (diffuse) impacts, it was possible to estimate their significance for the hydrology and ecology of wetland area situated along the river reach. The results showed that the floodplain land use has a significant local effect on the water levels and the related extent of flood inundation. Operation of the flood reservoir also has an impact on the river system.

► Impact of reservoir management and land use change on the Upper Narew flows.
► Application of Global Sensitivity Analysis to derive spatially distributed indices.
► Comparison of management policies at extreme and average water conditions.
► Floodplain land use has a significant local effect during all examined conditions.
► Operation of the reservoir has an impact during average water conditions.