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Zmiany warunków wodnych na obszarach leśnych w sąsiedztwie zbiornika wodnego Maziarnia

Boczoń A., Pierzgalski E., Tyszka J., Wiencław E.

Czasopismo Techniczne. Środowisko

2005

R. 102, z. 10-Ś

5--15

Retention of water in surface water reservoirs is one of the ways in which water resources can be enlarged. The impact of reservoirs on the adjacent natural sites depends on many factors, i.a. on hydrological and geomorphological conditions deciding on the circulation of surface and ground water near the reservoir. Its impact both positive and negative can change in time. An example of such changes was recorded from the vicinity of the Maziarnia reservoir, the initially positive impact of which on the surrounding forests of the Kolbuszowa forest district changed after several years of the functioning, and it caused negative changes in forest habitats. A partly lessening of water deficits in the areas of joint catchments of Łęg and Trześniówka Rivers, occurring mainly in the period from May to September, was the main aim of that reservoir made in 1988.It was made also for i.a. ensuring sufficient amounts of water for feeding neighbouring fishing ponds and irrigating meadows and pastures. The total volume of water collected in the reservoir is about 3860 thousand m[^3], the area is about 160 ha, and the mean depths is 2,4 m. Edge surrounding ditches of total length of 4,6 km were made along both edges of the flooded terrain. Due to social and economic changes, as well as to financial limitations occurring in the recent years, the role of the reservoir has been limited, and it serves now primarily as a tourism and recreational object, a source of energy for a water power plant (up to 50 KWh), a place for breeding fish, and as a flood preventing reserve. The depth of ground water table in the neighbouring forest areas was 1-3 m deep on the average, before the construction of the reservoir was made. The ground water came higher, but less than 1,0m under surface was only in (BMw).In the first year after filing the reservoir, a small rise of ground water was recorded, and it was estimated as a bettering of water relations in the forest sites. However, in several recent years a transformation of forest ground vegetation was recorded; raising the ground water table and a dieback of pine oldgrowths accompanying the former factor caused it. A computer model and field research was carried out for identification of causes and determination of methods refraining the negative impact of the reservoir on water relations in the forests neighbouring to the reservoir. A potential outreach and the speed of changes in water relations at various reservoir exploitation variants were determined with the FEMWATER model. The field research covered observations of ground waters in measuring wells and piezometers, and determination of the range of habitat changes.It was found from the model research verified with on field measurements that the ground water table may rise in the distance of 500-750 m on the areas located outside the left side of the reservoir, and 600-1500 m outside the right side of it. The analysis of the material collected showed that high precipitation in the period 1994-2000, being higher in individual years by 20-40% than the average from the period, was the main cause of changes in the reservoir impacts. The report presents the scope of habitat changes and the needs for activities aiming to regulation of water relations, covering i.a. changes of reservoir exploitation rules, and a development of a drainage system equipped with weirs that make possible to ground water table regulation.