This thesis looks into features of the volume flux in the narrow Drøbak strait, and water level changes in the inner Oslofjord.
Earlier measurements suggest that the volum flux in the east
course of the strait, calculated from one current profile at the deepest point of the sill, is only 50 % of the total volume flux in the strait, calculated from water level changes in the Inner Fjord.
Because of the Drøbak Jetty it was expected that most of the volum flux would be in the east course of the strait. This result is confirmed by current measurments carried out in connection with this thesis.
Three different methods is used to calculate the volum flux. The first is the method mentioned above, which uses one current profile measured by a bottom mounted acoustic current profiler.
The second method derivates the water level and multiplies with the water area of the Inner Fjord. The water level was thoroughly examined by three different pressure sensors mounted at suitable positions, in addition to two sensors runned by Statens Kartverk (Oslo harbour and Oscarsborg). No big differences was found in phase or amplitude. The biggest difference in phase was between Oscarsborg and Oslo harbour (5 minutes). The lowest amplitude was at the Steilene station (94 % of the value at Oslo harbour). The water level was also examined by a numerical model with resolution of 200 meters.
The third method used direct current measurments from a vessel mounted current profiler (VMCP). The volume flux was calculated in two diffrent sections, one in the east course right over the sill
and one south of the sill covering the entire strait. Measurments from the first section, gave a volume flux comparable with the results from the bottom mounted current profiler, which was less than the continuity equation suggested. Measurements from the latter section, gave a volume flux which was a little more than the continuity equation suggested.
Consequently this thesis offers no evident answer to the question about the volume flux, apart from that the estimates of the volume flux in the east course is too low and that the volume flux over the Drøbak Jetty is greater than assumed.