Thematic group leader Ruta Medne, institute “BIOR”

The hydromorphological characteristics of rivers are one of the main factors that determine the ecological quality of watercourses, as well as the fauna of fish and other aquatic organisms. With the development of human economic activity, rivers have been straightened and transformed into water drains, dammed and flooded to harness the power of water and facilitate water extraction, as well as altered in other ways. The operation of small power plants and water mills in most cases is also associated with changing the hydrological regime of watercourses.

In order to reduce the impact of hydromorphological changes within the project, research works have been carried out, the potentially most useful demonstration measures to be carried out in the river have been identified, and the implementation of these measures has also been started. The implemented measures are aimed both at increasing the diversity of habitats in the once straightened or otherwise modified watercourses, and at restoring the possibilities of fish migration in the culverts of highway crossings and other objects.

Research works on the hydromorphological quality of rivers were carried out in 2020 and 2021, when four rivers – Aģe, Mergupe, Auce and Zaņa, as well as several of their tributaries – were mapped along almost their entire length. Smaller-scale research works have also been carried out in the additional facilities of the project. Then, based on the results of the research and in cooperation with local municipalities and other interested parties, lists have been prepared that identify the potentially most useful demonstration measures for the improvement of hydromorphological quality in each river.

Currently, only one of the demonstration measures has been fully implemented – environmentally friendly maintenance measures for the “Mazupīte” watercourse. As part of this, not only was the cleaning of the watercourse bed carried out, but also measures were implemented (man-made stone piles were removed, sedimentation basins were built, artificial rapids were built, etc.) to increase the hydromorphological and ecological quality of this watercourse. In the near future, we will also carry out similar works on the straightened section of Aģe river. The planning of several measures to improve the possibilities of fish migration in Mergupe, Zaube and other rivers is also nearing completion, after the end of the period of fish spawning and caviar development, we will start implementing them.

In the project, we have also carried out the necessary measurements and, using the MesoHABSIM model, calculated the necessary ecological throughput for each of the small HPPs located in Aģe, Mergupe, Auce and Zaņa rivers, and prepared recommendations for more environmentally friendly operation of the small HPPs.