The Pšata river basin is defined as a 4th level hydrographic area (HGA IV) according to the national classification of the hydrographic areas. It is a hydrographic sub-area of the Sava catchment (HGA I, 10.675,2 km2), belonging to the Danube river basin. With the total surface area of 147.9 km2 the Pšata catchment represents 0.73 % of the Slovenian national territory. The total length of the watercourse network in the catchment is 364.4 km, with the Pšata river length being 28.8 km.
It is predominantly covered by agricultural land (48,1 %) and forests (40,8 %), followed by urban areas (11 %). The agricultural land and the urban areas are concentrated in the catchment lowlands, i.e. the Pšata valley, while the forests predominate in the hilly part of the catchment landscape. The agricultural land is intensively managed and thus largely degraded, while the forests, although economically used, are relatively well preserved, resulting in a significant proportion of forested area having a EU protection status (Natura 2000). Majority of the land in the catchment is privately owned (84,8 %).
The area under Natura 2000 is 1,523 ha (10.3 % of the total catchment area), and the area under national or local protection status is 2,463 ha (16.6 % of the total catchment area). Natura 2000 areas completely overlap with the areas under national or local protection status. The Pšata river has no EU protection status, however, one of its tributaries, the Dobovšek stream, has the status of Natura 2000. Some stretches and tributaries are protected according to the national legislation as natural assets.
The Pšata river crosses five municipalities: Cerklje na Gorenjskem, Komenda, Mengeš, Trzin and Domžale. The total number of inhabitants in all five municipalities is 63,050. Being a part of the central Slovenia region all five municipalities are highly developed, rating among top 5% of all municipalities in Slovenia.
Pšata is a lowland watercourse with a torrent-like character. During high flows, the water has significant erosive power. Photo: Urša Koce
The Pšata river has a pluvio-nival hydrologic regime and is torrential in its character. It originates in the southern foothills of the Kamnik-Savinja Alps and flows into the Kamniška Bistrica river, just a few kilometres before its outlet to the Sava river. The Pšata specific runoff (14.1 l/s*km2) is relatively low compared to other major watercourses in its parent Kamniška Bistrica catchment. Its average discharge between 1981‒2010 was 1.33 m3/s, with peak discharges in November and December.
Extensive past hydromorphological alterations and current maintenance works, rooted in the traditional flood control paradigm, as well as runoff from the agricultural and urbanized areas represent the main pressures to the Pšata river, the result of which is its moderate ecological status, as assessed according to the EU Water Framework Directive.
Being a lowland watercourse with regular flooding in the past, the Pšata river has been considerably regulated since the mid of the 20th century with the main purpose of flood control, resulting in extensive hydromorphological modification. Over the decades, its originally meandering riverbed has largely been straightened, cleared of riparian vegetation and consolidated, including construction of a number of weirs.
In the 1960’s a flood control channel (9.6 km) was constructed, starting at about the middle of its course, to divert the flood waters directly to the Kamniška Bistrica river and protect the downstream settled areas and agricultural land from every year flooding. The urbanization along the river increased largely after the construction of the flood facility and so did the intensification of the agricultural use in previously flooded areas, shifting from extensively managed wet meadows to intensively managed arable land, including the use of pesticides and artificial fertilizers.
However, the flood protection measures, including the channel, have been mostly designed for discharges up to Q100 and are thus ineffective in case of extreme events such as those related to climate change. For example, the recent extraordinary precipitation event that occurred on 3rd-4th August 2023 in the northern part of Slovenia resulted in catastrophic floods in a large part of the Pšata catchment.
The Pšata channel was built after World War II with the aim of eliminating annual floods in the area of the present-day Municipality of Mengeš. Photo: Urša Koce
As part of the implementation of the EU Floods Directive, three areas of significant flood risk have been identified within the Pšata catchment, but the surveys have not been completed yet and in reality, the total flood risk area is considerably larger (as it turned out in the recent floods).
Following the existing flood control paradigm of questionable effectiveness, the Slovenian Flood risk management plan 2023‒2027 sets a high priority for planning and construction of grey (technical) flood control infrastructure, without any prior consideration of alternative measures such as Nature-based solutions.
