Glossary
Region
Regions are used to have some finer control over which 2D model output is assigned to which 1D cross-section. If no region are defined, 2D model output is assigned to cross-section using k-nearest neighbour. This is not always a good approach, for example if a tributary or retention area. In the figure a section of the River Meuse is plotted near the Blitterswijck retention area. The retention area is demarcated from the main river by levees. Cross-sections generated for the retention area should therefore not 'eat out of' the area of the main channel - which could results in a small cross-section non-physical constriction of the flow.
Section
Section are used to divide the cross-section between floodplain and main channel (e.g. the 'floodplain' section and the 'main channel' section). This distinction is only used to assign different roughness values to each section.
Water level (in)dependent geometry
It is often not possible to start the 2D computation from a completely dry bed - instead some initial water level is present in the model. This initial condition divides the 1D geometry in water level dependent part and a water level independent part. Below the initial condition, we cannot take advantage of the 2D model to tell us which cells are part of the conveyance and which cells are wet. Instead, the water level is artificially lowered in a number of steps to estimate the volume below the initial water levels.
Summerdikes
Summerdikes are a Dutch term for levees that are designed to be flooded with higher discharges, but not with relatively low floods (i.e.: they withstand summer floods). They contrast with 'winterdikes', which are designed to not flood at all. Summerdikes effectively comparimentalise the floodplain. They can have a profound effect on stage-discharge relationships: as these levees overflow the compartments start flowing which leads to a retention effect. Such an effect cannot be modelled using regulare cross-sections. SOBEK therefore has a 'summerdike' functionality.
Control volume
A control volume of a cross-section is the geographical part of the 2D model that is associated with that cross-section. Contol volumes are assigned by k-Nearest Neighbour classification.
Note
Control volumes are the equivalent of WAQ2PROF's sobekvakken
Lakes
Lakes are water bodies that are not hydraulically connected to the main channel in the first few timesteps of the 2D model computation. They do not contribute to the volume present in the control volume until they connect with the rest of the river and will not feature in the water level independent computation. Water bodies that are connected to the main channel in the first few timesteps do count as volume. However, as these likely do not contribute to conveyance, they will be flagged as 'storage' instead.
Cross-section location
The cross-section location is defined in the
CrossSectionLocationFile.
Total volume
The Total volume refers to the volume of water [in m\^3] within a
Control volume for a given water
level at the Cross-section location{.interpreted-text
role="term"}. The total volume is the sum of the
Flow volume and the
Storage volume.
Flow volume
The Flow volume is defined as the volume of water [in m\^3] for
which the conditions for flowing water are met. This volume is
considered to be available for the conveyance of water through the
Control volume.
See distinguish_storage
Storage volume
The Storage volume is defined as the volume of water [in m\^3] for which the conditions for flowing water are not met. Storage volume does not contribute to conveyance, but serves only for water retention. Examples include groyne fields and
See distinguish_storage
Total width
See Total volume
Flow width
See Flow volume