Observations from an inspection of the area

The visual inspection of the area showed that the constructed erosion protection has functioned well. The water transport in the river varies heavily in spite of being partly regulated, and can seasonally be very high. The current is then very strong and the water level reaches almost up to the crest of the erosion protection.

However, no damage to this or minor slides or slips along the riverbanks can be observed. The vegetation is fairly abundant in most of the remaining natural slope below the eastern part of the excavated area. It partly originates here from the time before the excavation because the stabilisation works affected parts of this slope only to a limited extent. The clumps of trees consist mainly of birches and alders, Fig. 5.

The vegetation on the excavated areas consists mainly of grass and different kinds of sedges. The ground is generally marshy and for most of the time there is free water or ice at the back of these areas. The excavated areas on the eastern slope were given a very small inclination and here the major part of the vegetation is of the type growing in marshes and fens. The excavation towards the north was given a somewhat larger inclination and most of this area is covered by grass. However, the conditions are wet at the intersection between the excavated area and the excavation slope at its back because of water seeping out of the slope. This is clearly indicated also by a band of sedges growing along this intersection, Fig. 6. That planting of trees has been performed can only be observed in a few isolated groups of trees.

There is one on the eastern excavated area at a point where the ground is slightly elevated and the conditions thereby somewhat drier. There are also a couple on the northern area in points where the ground is similarly elevated or close to the crest of the slope towards the river and consequently relatively dry. A few smaller groups of birch trees have also been established on the excavated area and in the excavation slopes. However, these are not planted but from natural growth, Figs. 7 – 9.

The south-easternmost part of the excavation was performed in steps with two separate terraces at different levels. During the excavation works, erosion protection had had to be applied to cover the slope between the natural ground and the upper terrace to prevent the upper sand and silt deposits from flowing out because of internal erosion. The excavation at the upper terrace had also been deepened and then supplied with a base and paved. This had been done in order to enable the execution of the works and to let the terrace serve as an extended parking area for Åtorp manor house afterwards. In spite of these extra measures, the ground is still relatively soft and heavy vehicles create deep tracks, except in extremely dry periods and when the ground is frozen. The terrace has nowadays ceased to be used for parking. Instead, it is used by the local tennis club, which has constructed two hard tennis courts. This construction covers about half of this upper terrace and has involved a slight rise of the ground in order to obtain sufficient drainage and stiffness, Fig. 10. The lower terrace has the same character as the rest of the excavated area in the eastern part, with marshy ground and vegetation of mainly sedges.

Fig. 5. View of the eastern slope towards the river and its erosion protection.

Fig. 6. Band of sedges at the back of the excavated area in the north.

Fig. 7. Planted group of trees in the eastern excavated area.

a)

b)

Figs. 8 a and b. Groups of planted trees close to the crest of the northern slope and in the north-east corner. In Fig. 8b, the European main highway E6 can be seen running on the other side of the river behind the excavated area.

Fig. 9. Natural growth of birch trees in the eastern part of the excavated area.

Fig. 10. The upper terrace in the south-eastern part of the area with tennis courts. Tracks from traffic on the intended parking area are clearly visible.

The ground surface behind the upper crest is mainly horizontal. Of the former houses on the eastern side of the road leading to Åtorp manor house, only a single dwelling house remains in the northern part of the area. The other houses and the cement works have been demolished and the bought-up estates are mostly covered by grass. A few paved areas remain at the location of the cement works, but no other installations. In the south-eastern part, a small warehouse for the carpentry factory remains. The ground around this is paved with sand and gravel for transports of wood to and from the warehouse. No signs of superficial slides or cracks can be observed and have not, as far as is known, been reported apart from a few small slides in the northern slope during and shortly after the execution of the stabilising works.

2.6.3 Field tests