Construction of new E6 Frya-Sjoa

Summary

This report presents the results from monitoring of four branches to the river Gudbrandsdalslågen (Augla, Lauvåa, Givra and Kolobekken) between the towns of Frya and Sjoa in connection with the construction of the new sections of the E6 motorway. The project was commissioned by the Norwegian Public Roads Administration (Statens Vegvesen). Macroinvertebrates were sampled to assess ecological status using the macroinvertebrate index ASPT and complemented with the EPT taxa (a biodiversity index). The field work was conducted during autumn 2012, autumn 2013 (before construction) and spring and autumn 2018 (after construction). Several factors make it difficult to assess the degree of effect of the construction project on the streams. The affected stretches of the streams are located near or at the valley bottom. The hydrology of each stream is quite variable; for example, Lauvåa and Givra can run dry during the year. Variable conditions affect biodiversity as well as making adequate sampling a challenge. Only Kolobekken and Givra could be used to assess the impact of the construction. For Kolobekken, the downstream station could be classified as having Good ecological status prior to construction and Moderate ecological status after the construction was completed. However, there is some uncertainty to this conclusion in that the upstream station also changed ecological status. For Givra, no change in status was registered. For Lauvåa, the upstream station had Moderate status before and after construction, whereas the upstream station for Augla was Moderate before construction but had Good status afterwards. At the time of sampling Lauvåa and Augla were dry downstream, and the impact of construction could not be assessed here. It is challenging to assess the effect of this kind of construction work on the aquatic community because the Water Framework Directive lacks standardized methods that can be applied. Such methods should take into consideration, inter alia, the combined effect of nitrogen compounds derived from explosives used during the construction and the resulting stone-debris that is carried downstream. All four streams have been modified with respect to hydromorphology, but only part of this can be attributed to the construction work. The upstream streambed rock formation of Augla can bear water downstream, even during periods of low flow. This allows organic material to accumulate in the interstitial spaces of the seabed which is favorable for the macroinvertebrates. However, according to the Norwegian web portal Vann-nett, Augla is no longer suitable for upstream migration of fish from the Gudbrandsdalslågen. This is probably related to the construction of culverts under E6. The cover of blasted rock-debris downstream can result in that the water can disappear completely from the surface for certain periods. This in turn may reduce macroinvertebrate production (which is an important food source for fish). It is also an advantage for the macroinvertebrates that there is a variety of patches of sand, gravel and larger rocks. This is not the type of streambed at Augla, Lauvåa and Givra found downstream from the construction area, and hence, these stretches of streambeds are less favorable for a good ecology. In contrast in this regard, the Kolobekken downstream stretch is more suitable for macroinvertebrates.