2949775676

74

A. Kaniecki

elevational drop of most of the rivers and of the bottom of the valley, lower

than 0.2%o.

The Warta and Noteć river beds in their lower courses, that is within the borders of the Prussian state, were regulated first, under Frederick II’s rule. Straightening of the bed of the lower Noteć and cutting the obstructing bushes away "...doubled the outflow, lowered the water level in the river and dewatered the areas of previously-flooded banks" (Surowiecki 1811). Straightening of the river-bed was accompamed by the digging of canals and ditches draining water from wetlands (Piasecka 1974). At that time cuttings were dug, arms of the river regulated, banks protected and the elimination of the redundant network of river arms begun.

In the bed of the Warta, along its middle and upper course, work aiming at improving navigation was undertaken before the beginning of the 19th century. The regulation of the Warta by the Prussian government involved removing weirs and objects obstructing navigation, planting extensive sand outwashes with shrubs, digging cuttings and stabilising banks.

Intensification of drainage work within the Wielkopolska Lowland took place after the annexation of the region by the Prussian state. In 1773, when as a result of the first partition of Poland a part of the Bydgoszcz region was annexed, the construction of the Bydgoszcz Canal connecting the Wisła with the Noteć commenced, and the eastern areas of the Noteć river valley were drained. Within one year of the annexation of Poznań province, in 1793, preparation of drainage system plans for the Obra river valley had started. However, extensive marshy areas existed in this region even up to the beginning of the 19th century. These were: in the north — the Noteć river marshes, and towards the west — the Oder and Obra Skwierzyńska river valley, towards the south the Warta and Obra valley and the Barycz river valley, towards the east — the upper Noteć valley. In addition, the valleys of the tributaries of the above mentioned rivers formed continuous tracts of swamps and marshes. Other larger marshy areas were: the Bachorskie, Dzimońskie, Buczkowskie and Oniczkowskie marshes and the valleys of the Orla, Gąsawka and Wełna rivers. According to historical records over 40 large marshy areas existed within the Wielkopolska Lowland at that time. According to F. Stryjewski (1980), in 1815 there were 1,175,000 ha of plough-lands and 1 million ha of grassland, including 587,500 ha of meadows and 412,500 ha of pastures. Marshlands covered 50,200 ha and forests 605,800 ha. Land melioration was undertaken on the largest scalę in the Obra river valley; it commenced in 1799 and continued up till 1806. At that time canals within the area of Wielki Łęg (Great Ash—Alder Forest) were dug: the 53.9 km Southern Canal, 57.6 km Northern Canal, 8.2 km Kościan Canal, 25.7 km Mosina Canal, 6.8 km Wincentów Canal and the 6.3 km Dźwina Canal. The total length of the canals built at that period amounted to around 158.5 km. They contributed towards improving the run-off of waters from the Obra river Great Ash—Alder Forest.