Reflections on the Somlyó Island

IN HUNGARIAN

The island of Somlyó is practically invisible from the Soroksári-Duna, just south of Budapest. Only three almost invisible landmarks reveal that a large island is hidden on the left bank between Ráckeve and Dömsöd. A bridge, a culvert and a lock ensure that you can find the hidden Dömsödi Holt-Duna, one of the most beautiful tributaries of the Soroksári-Duna.

The Dömsödi Holt-Duna surrounds the largest island of the Soroksári-Duna, the Somlyó Island, from the east. This alone makes the Dömsödi Holt-Duna the longest tributary, at 6.5 kilometres. However, the accurate lenght can be doubtful, since the tributary was cut in two in 1941 [1] with the construction of the Dömsödi Drainage Canal, which divided it into a 4.1-kilometre and a 2.4-kilometre section. It was built at the thinnest point of the Somlyó Island, where the island narrows to only 37 metres. This channel also bisects the odd-shaped Somlyó Island. The lower part, which is called "Upper Island" for the sake of clarity in Dömsöd, has already been described on this blog. 

On 22 October 2020, we walked the upper 4.1 km section of the Dömsödi Holt-Duna on the Somlyó Island side. The walk is not easy, at least not without a lot of patience. The main difficulty comes from the mosaic nature of Somlyó Island. This mosaicism is reflected in the settlement structure, i.e. the layout of built-up areas is not uniform, with clusters of weekend houses often interrupted by ploughs and woods. The topography is also varied, at least for a lowland Danube island, with many deeper parts, formerly remains of old tributaries, where most of the inland water is now drained. In many places there are still traces of former land use, farmland, which has not yet been completely eradicated by the parcelling out of land for weekend houses. Presumably, due to the considerable size of the island (3 square kilometres), this will take more time.

The width of the Dömsödi Holt-Duna is relatively narrow compared to its length, varying between 15 and 30 metres, which can be further narrowed by the reeds on the river banks. It receives some fresh water from the Soroksári-Duna at the island's head towards Ráckeve via an iron pipe under the road, but this is not enough to make it a living river. The estuary can reach a depth of 1.5 metres in places, but this is constantly decreasing as the low flow rate is unable to flush out the accumulated organic matter. It is often covered with frogweed, with reeds appearing in the lower part, close to the sluice. 

On both sides of the backwater, nature reigns, despite the mosaic of coastal cottages that in some places approach the Dömsödi Holt-Duna. There is no direct road along the banks, precisely because of the cottages, but access is easy on the paths perpendicular to the Dömsödi Holt-Duna, although some of these are closed by the residents. Where there are paths along the shore, they are mainly used by anglers. As well as illegal dumps. The left bank, the Danube–Tisza Interfluve, is more monotonous, with forests interspersed with arable land and no passable paths along the banks.

Since the closure of the Soroksári-Duna (1872), the Dömsödi Holt-Duna has not only lost a large part of its discharge, but the riverbed has also narrowed. Evidence of this can be found in the middle section of the backwater, where a ditch runs parallel to the road and is separated from the dead section by a bank. This ditch acts as a kind of suspended basin, filling with water in wet weather, marking the width of the former channel. Which was around 60 metres 150 years ago.  

Strangely, a little island could have formed in this narrow branch. The most interesting hydrological formation of the Dömsödi Holt-Duna is this single unnamed island, located between the line of Kála and Tűvelevelű streets. It is 140 metres long and has a maximum width of only 20 metres. It is much easier to find it on maps than in real life. The streets leading to this island either end in a reed bed, from where you can't see anything, or are closed off by a wire fence. On the opposite bank is also a holiday resort, but a small dug canal leads down to the top of the island (see picture below). There is also an impenetrable "jungle" on this side, but the lower tip of the island is not only inaccessible because of this, but also because of the upsilted backwater. 

This is the smallest island in the whole Soroksári branch, except for the floating bogs. As its upsilting is at an advanced stage, it is worth visiting it as soon as possible. The best way to do this is by canoe, as we found out on our tour. You only have to lift it twice. 

[1] SZABÓ BENEDEK: A társulatok szerepe a Duna-Tisza közi hátság vízgazdálkodási problémáinak megoldásában. in.: A Magyar Hidrológiai Társaság XIII. Országos Vándorgyűlése I. kötet (Baja, 1995. július 4-6.)

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