engleski

POositive and negative influences of hydroelectric plants on Drava river to groundwater quality

At the confluence of the Drava and Mura river there is spacious lowland where a significant gradient of the Drava river is preserved. Such conditions were favourable for construction of three hydroelectric plants along the total of 60 kms of the Drava watercourse in Croatia from the Slovenian border to the mouth of the Mura River. Boundary conditions of phreatic aquifer were strongly affected by construction of the three mentioned hydroelectric plants. The formed accumulation lakes caused ground water recharge and elevation of the water table, and on the other side, drainage channels were cut deeply into the aquifer, which resulted in strong ground water drainage. In this paper, changes in nitrate content of the groundwater from the two most important well fields in the area are considered. Upon construction of the upstream dam, the nitrate content in both well fields was increased from approximately 2 to over 20 mg N/l. The principal cause for this is found in expansion of the drainage area in the region with intensive agriculture and reduction of the groundwater recharge from the Drava River. After the second dam was completed, the nitrate content in one of the well fields was gradually diminished to under 5 mg N/l, mostly because of the increased recharge from the newly formed accumulation lake, which is interpreted as an illustration of the possibly positive influence of construction of hydro-electric power plants.

phreatic aguifer; groundwater quality; hydro-electric plants; hydogeological condition.

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