Tide gauges are used to assess sea level changes. Usually, they are placed on the coast (piers), which can be unstable. Consequently, the vertical movement of the tide gauge should be included in the series of observations. The paper deals with the stability of the tide gauge Station Koper (MP Koper), the stability of which was determined relatively on the basis of the levelling network, which was stabilised nearby. The stability of the individual benchmarks was analysed and the velocity vector of vertical displacement of each benchmark was determined with respect to the benchmark 9000 tide gauge. The stability of the tide gauge was also determined in a global reference system by using the series of GNSS observations of the KOPE continuously operating reference GNSS station. The KOPE station is stabilised at the MP Koper and is included in the Slovenian GNSS network of the SIGNAL continuously operating reference network of permanent stations. The vertical velocity vector of the point KOPE was compared with the vertical velocity vectors at other tide gauges, which are located along the Croatian coast, and the tide gauges in Trieste.
Key words: tide gauge, sea level, vertical movements, levelling network, GNSS