Mokrzec – Wisłoka River

Building of bypass

Wisłoka River – km 69+720
community: Pilzno
place: Mokrzec
Planned term of start:
IVth quarter 2019
Planned term of end:
IInd quarter 2021
Anticipated cost:
7 779 272 Polish zloty

Why do we interfere in a river?

A modernized weir was built in 2000 in order to flood aggregate excavations as a form of reclamation of desolate areas. The area of created Pilzno reservoir is above 230 ha. Even though an existing weir is equipment with a fish pass (at the left bank), it is still an impenetrable obstacle for aquatic organisms.


Modernized structure

A rubber coating weir allows for possible changes of damming from 1,90 m (at complex empty coatings) to 4,5 m at normal work of devices. A small hydroelectric power plant is located by the weir.

At weir chamber, a fish pass is built which stopped functioning after building a small hydroelectric power plant at the opposite side from the fish pass. It resulted in concentration of main masses of water and fish gathering as an result of attractant current at the side of hydroelectric power plant and therefore uselessness of existing fish pass. Besides both the weir and the reservoir created as a result of damming water caused stopping of sediment bed load transport. It disturbed natural processes in riverbed below these structures – a strong bottom erosion below an inlet to fish pass occurred.

Planned modernization

Modernization of dam includes building of a fish pass in a form of a bypass    evading weir, at its right bank next to small hydroelectric power plant.

The total length of this fish pass will be up to about 430 m. It will consists of 43 pools of size 4,0 x 7,0 m and 2 resting pools. The bottom of the pools will be covered by a stone overlay. The pool bars will be made of boulders of different dimensions.

An inlet from the side of upper water will be made of a reinforced concrete road culvert. An outlet from a fish pass from the side of lower water will consist of a reinforced concrete dock with wings. Two concrete bars with 1,0 m width aperture will be designed in the dock. In order to increase bottom roughness and to improve conditions for fish migration, a rip-rap will be stabilized at bottom.

Stages of the construction

resting pool for fish

Construction completed (September 2021)

fot. ZBE
fot. ZBE

Fish migration monitoring (October 2021)