Summer - autumn floods in Dviete floodplain
During the summer and autumn of this year, repeat increase of water level was observed in Dviete floodplain, caused by frequent and continuous precipitation in catchment of river Dviete. Almost all summer and autumn weeks were rainy. According to the data from weather station of Daugavpils University, located in Putnu sala, beginning and end of June and August, middle of July, first half of October and middle of November were especially rainy.
There are 15 groundwater wells installed within the LIFE+ project to monitor changes of groundwater level before and after restoration of Dviete riverbed. Water level in groundwater wells sensitively responded to the fluctuations of amount of precipitation, rising even by 0.5 m during a week, when amount of precipitation had increased by 10 mm. Most expressed increase of groundwater level was observed in the wells, located closer to Dviete river, especially in the first half of November, when during two weeks about 50 mm of rain fall in the region of Dviete floodplain. Water level in lowest wells consequently rose for about 1.0-1.5 meters, reaching about 88 m above see level in the middle of November. Thus Dviete floodplain near Putnu sala was flooded. In the middle of November 12 out of 15 groundwater wells, arranged during the LIFE+ project, were over-flooded. Also all old groundwater wells at the bank of Dviete river oxbow were under the water.
Reason for flooding of Dviete floodplain this autumn was not only local weather conditions, but also significant increase of water level in Daugava river downstream Daugavpils.
According to perennial data from hydrological observations, flooding of Daugava downstream Daugavpils, caused by rainfall, can be observed from the middle of May until the middle of December. Duration of floods can be from 15 till 102 days (39 days on an average). Date of average perennial maximum of summer – autumn floods in Vaikuļāni hydrological post (closest to Dviete floodplain nature park), is November 3 (probability 58%), the second most frequent observed maximum date is June 28 (probability 42%). Maximal levels of summer – autumn floods can reach 89.65 m above sea level here, and average perennial level of summer – autumn floods for this post is 86.45 above sea level.
So the level of autumn flooding, observed in Dviete floodplain in November 2012, significantly exceeded average perennial index for this section of river Daugava (by about 1.5 m), still it is not new hydrological record.
Autumn floods hinder removal of bushes in floodplain grasslands, planned within the LIFE+ project. It is planned to restore about 40 ha of overgrown grasslands during this autumn and winter; till now three agreements on grassland restoration are signed, covering area of 34.8 ha in total.
Dāvis Gruberts, Ilze Priedniece
23.11.2012.
