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Łódź: Stormwater retention and ecological   quality improvement

The River   Sokołówka is a small, urban stream running through the northern part of the   city of Łódź, the third largest city in Poland. The catchment spans urban, as   well as agricultural and natural areas. In the early 1930s, the upper reaches   of the river were straightened, deepened and partially canalized. The main   channel of the urban stream was converted into a collector for 50 stormwater   outlets. These developments resulted in adverse effects on the urban and   surrounding ecosystems, and the Sokołówka and adjacent rivers were polluted   with discharge from combined sewage and stormwater overflows several times   per year.

Most of Łódź   rivers work as a part of a combined sewerage system of the city. During heavy   rains, rivers intercept waters from overflows and rain water. Shortage of   stormwater retention reservoirs is one of the reasons for pollution of the   biggest river of the city, the River Ner, which receives combined sewage from   the entire city.

The   repeating problems related to pollution, overflows and ecological degradation   made the city look for possibilities of stormwater retention, and for   improving the ecological quality of the rivers, thus creating friendlier and   healthier public space.

The city   of Łódź has implemented a comprehensive urban development programme on water   and river restoration, part of which has been the restoration of the River Sokołówka . For the River Sokołówka, a   sequential stormwater sedimentation-biofiltration system was implemented,   which prevents the influx of pollutants into the river during high flows   (Zalewski et al. 2012). Five retention reservoirs were constructed in order   to increase river retention and pollution absorption capacity. These measures   went hand in hand with development plans for a further rehabilitation of the   river valley (Wagner and Breil, 2013).

As a   result of the measures taken, the river and its valley have turned into an   attractive residential and recreational area which has contributed to the positive   economic development in the wider area (Wagner et al. 2007). The creation of   new green areas as part of the restoration activities has had positive   influence on the quality of the   inhabitants’ life and their health.The restoration of the Sokołówka River has been used as a   demonstration case to gather experience that can then be used for further   replication on other streams and rivers crossing the city. The demonstration   projects implemented by the city of Łódź have played an important role in   creating visibility, interest and cooperation, and as such have been vital in   the scaling-up strategy of the project.    

Zgierska   pond in the urban catchment of the Sokolowka River after restoration. (Photo:   ©Anita   Waack-Zając)

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