Because of the observed rate, Solomon's Island was chosen as the first permanent GPS site for this project. But the slope of the coastal plain in the region is very shallow, being in many places less than 1 part in 1000. And this rate of loss can persist for decades. Local effects make the tide gauge data difficult to interpret It is important to remember that tide gauges are primarily a navigation aid. As such, many of these tide gauges are located near ports and other growing population centers.
Tide gauges measure sea level changes relative to the land on which the the tide gauge rests.
By itself, a tide gauge cannot tell the difference between local crustal motion and sea level changes. The following figures illustrate this point. The dashed red line is at a constant height in all figures. In the first figure, the water level is fixed but the land has fallen. In the second figure, the land is stable but the water level has risen.