175 A Study of Flow Conditions Aimed at Preserving Valuable Wetland Areas in the Upper Narew Valley Using GSA-GLUE Methodology Adam Kiczko 1 , Renata J. Romanowicz 2 , Jaroslaw J. Napiórkowski 1 Abstract The aim of this paper is to investigate the possibilities of reaching desired flow conditions in the reaches of the ecol- ogically valuable Upper Narew river using specified river management and training (or engineering) techniques. The study is based on Global Sensitivity Analysis (GSA) and Generalised Likelihood Uncertainty Estimation (GLUE) techniques applied to a 1-D river flow model. The locally conditioned GSA is used to estimate the influence of each conservation action scenario. 1. Introduction In recent years alarming changes have been observed in the Narew river hydrologic regime, manifesting in the reduction of mean flows and shorter flooding periods. This results in a serious threat to the rich we- tland ecosystems. Many local management activities refer to this problem and there is a number of con- cepts of conservation actions. The goal of this paper is to analyse the influence of these activities aiming to preserve the semi-natural state of the largest area of marsh ecosystem in the study, which is localised along the Ploski-SuraŜ reach. We apply the General Sensitivity Analysis (GSA) technique together with Generalised Likelihood Un- certainty Estimation (GLUE) approach to obtain a quantitative measure of significance of each inference in the river system. The results of the analysis are important for a future formulation of a water manage- ment system in the region. 2. Study area The Valley of the Upper Narew is located in north–east Poland. The study area includes a 70 km long re- ach that begins at the Siemianówka Water Reservoir outflow and ends at the water level gauging station in SuraŜ (Figure 2.1). Generally, with the exception of areas close to the reservoir, built in the early 1980- ties, this part of the river is not modified by human activity. The valley is approximately 1–2 km wide and 7–10 m deep. It has been shaped by a meandering river channel and presents a natural form of lowland river system, with relatively small water slope values, at the level of 0.24 ‰. The annual river discharge varies from 5.72 to 15.50 m 3 /s. In this area the river generally flows in one channel. However, due to the existence of meanders and old river beds, this river system has a rather complex structure during high flows. Almost 90% of the valley is occupied by rich wetland ecosystems, mostly by marshes (55%) and pe- atlands (31%). The remaining 10% of the area is covered by postglacial mineral soils and sand dunes. Moreover, mud soils filling the old river beds play an important role in maintaining local ecosystems. In these conditions only extensive agriculture is possible in the valley terrains. This semi–natural charac- ter and environmental conditions of the region indicate that this part of the Narew valley has a great value from the ecological point of view (Dembek and Danielewska, 1996). 1 Institute of Geophysics of the Polish Academy of Sciences 2 Environmental Science Department Lancaster University