Abstract: The Nida River flows in Świętokrzyskie district over the valley which is used mostly by agriculture. At present in it’s lower run the river is quite danger during floods due to the lack of small retention. This could be easily restored after removing of the embankments. After the increase of the retention by the opening of the valley areas, the reflection of the river itself on the close to nature run was calculated. In the paper the results of the flooded zones on the reach length of 10.3 km are presented. For the case 103 cross-sections distributed every 100 meters were prepared. The simulations of flooding by discharges between 1 m3 · s–1 and Q_1% were performed.

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