In the Latvian landscape, drainage ditches are so common that we often hardly notice them. They run alongside fields and roads, connect agricultural land to larger watercourses, and help drain excess water. However, water flowing through these ditches also carries soil particles and nutrients that can affect the water quality of nearby rivers and lakes. This issue is particularly important in polder areas, where water levels are regulated by man-made systems.
The LIFE RiverFlow project focuses on improving water management in polders while maintaining their economic importance and reducing their impact on aquatic ecosystems.
What are polders and why are they needed?
Polders are low-lying areas that have historically been prone to flooding. In these areas, water cannot drain efficiently into nearby watercourses naturally, so it must be pumped out. Polders are separated from surrounding waters by protective embankments, while excess water is collected through networks of ditches and drainage systems and pumped outside the polder.
Latvia has several dozen polders covering a total area of tens of thousands of hectares. They are located in different parts of the country, including the Lielupe River basin, the area surrounding Lake Babīte, near Lake Lubāns, and elsewhere. Polders play an important role in agriculture and in protecting populated areas from flooding.
Polder systems consist of protective embankments, drainage ditch networks, and pumping stations that transfer collected water outside the protected area. Without these systems, the surrounding land would remain waterlogged for extended periods, making agriculture, forestry, and residential use more difficult.
One example is the Auce polder, which is also a demonstration area of the LIFE RiverFlow project. The Auce polder pumping station was reconstructed in 2017 and equipped with energy-efficient pumps. Their combined power exceeds 100 kW, and the pumping capacity reaches 1.7 cubic metres per second. This illustrates the substantial volumes of water managed in polder areas and the importance of keeping this infrastructure operating continuously.
Watch the video to discover how polder systems work and what improvements LIFE RiverFlow is planning!
However, polder management is not only about removing excess water. An equally important question is what this water carries into nearby rivers.
What does water carry into rivers?
Rainwater and snowmelt flow through soil, drainage systems, and ditches into larger watercourses, carrying soil particles and nutrients, mainly nitrogen and phosphorus compounds. Although these substances are essential for plant growth, excess nutrients can be washed away from agricultural land and enter rivers and lakes.
Excessive nutrient inputs contribute to eutrophication – increased growth of algae and aquatic plants, which reduces water quality and can negatively affect fish and other aquatic organisms. Drainage systems help reduce soil erosion from agricultural fields, but they can also accelerate the transport of dissolved nutrients into watercourses through underground drainage pipes.
Therefore, it is important not only to drain excess water efficiently but also to reduce the amount of pollution it carries. Even a small ditch is part of a larger drainage network through which nutrients can reach major rivers and eventually the Baltic Sea.
Can water be drained more intelligently?
Modern water management involves not only draining excess water but also regulating its flow and reducing pollution. One solution is controlled drainage, which uses special water-level control structures to regulate water outflow from agricultural fields. This helps retain soil moisture for longer, particularly during dry periods, and can reduce nutrient leaching, especially nitrogen compounds.
Another solution is sedimentation basins – specially designed widened or deepened sections of drainage ditches where water flow slows down, allowing suspended soil and organic matter particles to settle. Some of the phosphorus attached to these particles can also be retained. Such basins are typically constructed before drainage ditches discharge into larger watercourses, and accumulated sediment must be removed periodically.
The two solutions complement each other: controlled drainage regulates water outflow directly from agricultural fields, while sedimentation basins capture some of the pollution further along the drainage system. Their shared objective is to reduce nutrient inputs into rivers while maintaining the economic functions of drainage infrastructure.
LIFE RiverFlow - testing solutions in the Lielupe river basin
The LIFE RiverFlow project plans to implement water management improvements in polder areas within the Lielupe River basin, including areas associated with the Auce and Svēte rivers. The project includes the construction of a controlled drainage system and a sedimentation basin.
Importantly, the project's objective is not to eliminate the functions of polders or stop the drainage of agricultural land. On the contrary, it aims to find ways to combine effective water-level regulation with a reduced impact on surrounding aquatic ecosystems.
Following the construction of these measures, the project will monitor agricultural runoff and nutrient levels. This will make it possible to assess water quality, evaluate the effectiveness of the measures under different hydrological conditions, and determine whether similar solutions could be implemented in other polder areas.
From a single ditch to the Baltic Sea
Environmentally friendly drainage solutions are not an entirely new approach in Latvia. The LIFE GoodWater IP project has already implemented measures to reduce pollution caused by runoff from agricultural and forest land. For example, sedimentation basins and other environmentally friendly drainage features have been installed in the Aģe and Slocene river basins to help reduce the transport of soil particles and nutrients into watercourses. LIFE RiverFlow builds on this approach by testing solutions in polder areas and evaluating their effectiveness under Latvian conditions.
Water management improvements in a single polder may seem like a small step compared with Latvia's extensive network of rivers and drainage ditches. However, every watercourse is part of a larger system. By reducing the amount of soil particles and nutrients entering ditches and rivers, it is possible to reduce pollution not only in nearby water bodies but also in aquatic ecosystems further downstream. In the case of the Lielupe River, this connection extends all the way to the Gulf of Riga and the Baltic Sea.
The future of polders is not just about how quickly excess water can be drained. Equally important is the quality of the water we discharge and the impact it has on rivers, lakes, and the sea.
