lost landscape

Riparian Forest In The Rainy Landscape

The landscape of the Strzyza was formed during the Ice Age, as a result of melting glaciers. Along the coastline of the Baltic Sea the glaciers created a very specific landscape, resulting in big height differences. The Strzyza starts its course on the Moraine plateau (140 metres above sea level) and flows towards Baltic Sea. It is 13 km long.

The Strzyza flows through the old, post-glacial gully, which was formed by the waters of the melting glacier. The Strzyza is the last tributary of the Vistula river, one of the most important watercourses, which drains the waters of Gdansk’s highland plateau.

On a regional scale, the Strzyza fulfills an important water drainage function for the moraine plateau, which is one of the rainiest areas of Poland, with 800-900 mm of rain annually. Heavy rainfall on the hills of the moraine plateau flows down towards the city causing annual flooding.

The uphill forested part of the creek has eight retention basins that store water during heavy rainfall. This solution offered by the government can store around 200,000 m 3 of rainwater, which is 5 times too little. During heavy rainfall some million m 3 of water per day falls on the whole watershed of the Strzyza. When the retention basins fail to store all the rainwater, the water starts to overflow towards the city.

The urbanized stretch of the creek is canalized or placed underground in concrete pipes. The geometrically shaped canal system of the creek is unable to absorb or slow down the rainwater coming from the moraine hills, which leads to dangerous flash floods.

29: Alnus Glutinosa tree, which is a common species for the riparian forest habitat, Fig. 30, 31: Major Natural areas of Gdansk in the scale of the city and the scale of Strzyza’s watershed. One of major natural areas are located on the edges of Moraine Plateau. The 140 m steep terrein difference made these areas uninhabitable.

flowing rainwater porous surfaces, sandy soils enable infiltration of rainwater

Sand recharged underground water table lack of porous surfaces in the city leads to floods Baltic Sea cloud formation wind towards land fast run-off through city evaporation during high temperatures higher air temperatures due to climate change

Fig. 36, 37: The lower part (floodplain) of the Strzyza creek lays on top of sandy, porous soils. Before urbanization of the Strzyza watershed flowing downstream rainwater was infiltrated into the soil. The rain was re-charging the underground reservoirs of sweet water. Fig. 38, 39: Nowadays, this whole area is mostly urbanised, with little to no porous surfaces. Sealed-off surfaces in the lower part of Strzyza stream lead to floods. Water has little to no space to infiltrate.

Fig. 40: The biggest rainfall occur in the mountains regions and by the Baltic Sea: 800-900 mm of rain annually, Fig. 41,42: On the regional scale the biggest rainfalls occur on top of Moraine Plateau, making it an important drainage on a regional scale. Fig. 43: The biggest rainfall occurs during hot summer months. The diagram shows the amount of rain falling during floods (x) in just one day in comparasence to waterfall during the entire month.

Urbanization of the Strzyza floodplain made this area more prone to flash floods. Rain has no place to nflitrate, so it flushes into the city, causing floods. (Fig. 44,45), Vegetation and spongy riparian soil play an important role in the local, regional and global rainwater cycles. It is important to acknowledge that Strzyza is not just a water line, rather it is an interconnected ecosystem. Its water is everywhere; in the air, soil and plants (Fig. 46).