History of regulation and melioration
Initially, Warta River had a character of aanastomosing river i.e. it flowedin many different beds which joined and split forming a complicated net.The whole area of the river valley was covered by extensive wetlands overgrown with a carr forest. This terrain was under strong influence of Warta and Odra which caused systematic floods during high water level periods.
Up to 1773 the natural state of the terrain changed only to a small extent, reduced to building single canals and drainage ditches that regulated the outflow of water from the wetlands situated out of the mouth area where settlements existed.
Significant hydrographic changes in the Warta River valley occurred in the end of the 18th century under the rule of Frideric the Great, during regulation work related to preparing a water way Wisła – Odra. This operation was undertaken to speed up the water runoff and to protect the area from floods. The regulation project was made by I.J Petri in 1765. The work began on a big scale in 1767. The work included:
· embanking Warta River from the north
· melioration of the whole valley
· construction of few canals close to the mouth section in which Warta should flow. The biggest among them is Frideric Canal (from “Prądy” up to Dąbroszyn village) and Frideric William Canal (from the bridge in Kostrzyn nad Odrą up to the mouth of the river) through which Warta River was directed north from former Kostrzyn. This canal is now the mouth section of the river
· barricading the old river mouth located near today’s Chyrzyno
· building a levee between Słońska and Kostrzyn in 1828-1832 at the left bank of Warta
· joining of the yet build left-bank levee in Słońsk with the Postomia River levee in1842
· building few pumping stations at the beginning of the 19th century in order to drain the polders that formed near the flood reservoir
As a result of all the mentioned actions, the area lying in the valley have been cut off from the strong influence of Warta and Odra what enabled to transform it into meadows and pastures initiating agricultural use. At the left bank of Warta between Kostrzyn and Słońsk a flood reservoir of about 51 km² has been formed. Because the conducted works did not affect much the area of the reservoir it has the most natural hydrographic system what increases its natural value.
All these investments ended the primary stage of melioraton work at the mouth section of Warta. In the 70s of the 20th century additional melioration was conducted on the Northern Polder. As a result of these works a rich net of basic ditches and gates was build. One of the curiosities of this system are melioration canals crossing, canals with diferent water level build one by one. You may see these interesting technical solutions near the pumping station close to the ferry passage in Oksza.