The Flinta River, Poland

The Flinta River is one of the main tributaries of the Wełna River in the Wielkopolska Region of central Poland. It is 27 km long and drains a catchment area of 345.47 km². The river channel is relatively narrow, with a bed width of 4–5 m, and has a gentle longitudinal slope of 1.2–1.3‰. Its average discharge is 0.50 m³/s.The river rises in wet meadows protected within a nature reserve at an elevation of 80 m a.s.l., and flows into the Wełna River at 59 m a.s.l. Flinta is a sandy-substrate river, typical of the Central European Lowlands, located in the Wielkopolskie Province of Poland.

Historically, the river was subject to regulation and land reclamation works from the 19th century onwards, which caused major ecological and hydrological changes. In recent years, more than a decade of research and restoration efforts has focused on improving its ecological status, including the use of low-cost wooden deflectors and plant basket hydraulic structures. In the past, the Flinta provided good habitat for brown trout, and today several initiatives aim to restore the species to the river. At present, the river is also known as an attractive and varied kayaking route, accessible mainly during periods of higher water levels, especially in spring.

Figure 1: The Flinta River location

Hydrological observations are collected at the water gauge station in Ryczywół (km 14 + 355 from the mouth). There is also a weather station within the catchment. Both stations are part of the Measurement and Observation Network of the Institute of Meteorology and Water Management – National Research Institute (IMGW-PIB).

Figure 2. Hydrogram for the Rryczywół water gauge between 2007 and 2022. Characteristic discharges: NSQ—lowest of the mean annual; SSQ—average of the mean annual (in this case it is bankfull discharge); SWQ—average of the annual high..

At the same time, average monthly flows (SSQ) remained relatively stable over the decades, amounting to 0.64 m³/s in 1951–1970, 0.73 m³/s in 1976–1995, and 0.61 m³/s in 2001–2020.

Figure 3. The variability of monthly average water flows in the Flinta River since the mid-20th century

Four measurement locations were selected within the Flinta River catchment area. All of them are situated in the lower course of the river, where the flows observed in the Ryczywół cross-section can be considered reliable. The selected sites include: Location 1 – Oxbow lake and flood polder; Location 2 – Mill pond and flood polder Piłka Młyn; Location 3 – Flinta oxbows: old channel and meanders; Location 4 – Flinta River mouth: ponds in the estuary.

Figure 4: Study sites locations in Poland in the Flinta River catchment area.

Figure 5: Location 1 - Oxbow lake and flood polder.

Figure 6: Location 2 – Mill pond and flood polder Piłka Młyn.

Figure 7: Location 3 - Flinta oxbows - Old channel and meanders.

Figure 8: Location 4 – Flinta River mouth - Pounds in estuary.

Archival cartographic materials were used to trace horizontal changes in the Flinta River channel over the past century and to assess the scale of its meandering. The analysis shows that the river course changed dynamically between 1888 and 1939. In the mid-20th century, the channel was regulated and significantly shortened. Since then, its course has remained largely fixed, supported by regular maintenance works such as deepening and dredging. Between 1981 and 2000, only minor changes were observed, mainly in the northern section. This was linked to the enlargement of a small flowing water body and the impact of the Piłka-Młyn weir, which shifted the channel slightly eastwards so that it now runs alongside the reservoir.