and coastal growth and to take measures if necessary. In the Coastal Memorandum, the Dutch Government decides to maintain the 1990 coastline by beach nourishment. The coastline in question is the low-water line. For practical application, the definition of this does not appear to be unambiguous, which is why the Memorandum also defines the momentary coastline (also called instantaneous coastline) (MKL) and basic Coastline (BKL). Each year, the shoreline to be tested ( TKL) is determined on the basis of the MKL, and if it threatens to come inland from the BKL, a sand nourishment is carried out. Definition of the instantaneous coastline The problem with the low water line mentioned in the 1990 Coastal Memorandum is that the height of the average low tide is well defined, but the position in the horizontal direction is not. See the attached figure, here the beach profile crosses three times the low water line. In fact, it is also not important to maintain a line, but to maintain the amount of sand in the active beach profile. To determine this volume, two heights are used, the average low water level (glw) and the height of the dune foot (dv). The height of the dune foot is basically determined by finding the intersection of the steep slope of the dune front and of the dry beach. In general, this theoretical dune foot point will be slightly below the sand. It is very difficult to redefine the height of the dune foot every year. Some administrators define the dune foot line as a certain elevation line, on which the dune foot usually lies. In relatively unalterable coastal sections, this is an acceptable approach. The method of determining the MKL is such that it is not very sensitive to the precise choice of the value dv. The location of the dune foot is thus determined by the height above NAP (National Datum, approx. Mean Sea Level) and the distance from that elevation line to the administrative coastline (Xdv). This administrative line has no physical meaning, but is simply the basis for survey work. The recipe for calculating the position of the MKL is: Determine the location of the dune foot The height of the average low water (glw) is determined The height h of the dune foot above average low water is calculated The sand volume A is calculated; A is the volume of sand