Groundwater Couplings¶
The 'Groundwater couplings' editor, available in the 'Model couplings' menu from the 'Setup' tree, allows the coupling of all or parts of the river and/or collection system network to a MIKE SHE groundwater model. It also allows coupling the river network to a FEFLOW groundwater model.
To enable groundwater coupling, tick the 'Coupling to MIKE SHE or FEFLOW' option in the 'Model type' editor.
The network items (rivers, manholes, soakaways or pipes) included in the coupling are those listed in the overview table at the bottom of the editor. Coupled network items are added or removed using the 'Insert' and 'Delete' buttons at the top.
The button 'Insert selected' will add all rivers, pipes, soakaways and/or manholes which are selected on the map and not already present in the list of couplings.
The following parameters must be configured for each groundwater coupling.
Identification¶
ID¶
The descriptive name of the coupling.
Type¶
The type of item from the network to be coupled to the groundwater model. The available options are:
- River
- Manhole
- Soakaway
- Pipe
Apply¶
This check box allows to toggle the Active status of the coupling on and off. The simulations will omit all couplings that are not active.
Location¶
River ID¶
Name of the river where the groundwater coupling should be applied. One river can be sub-divided into several reaches. A reason for doing so could be to allow different riverbed leakage coefficients for different reaches of the river.
From lowest chainage¶
Chainage of the start of the river reach to be coupled to the groundwater model.
To highest chainage¶
Chainage of the end of the river reach to be coupled to the groundwater model. If the highest chainage is set equal to the lowest chainage, the coupling will be performed in a single point on the river.
Node ID¶
Name of the manhole or soakaway where the groundwater coupling should be applied.
Pipe ID¶
Name of the pipe where the groundwater coupling should be applied.
Exchange attributes for rivers¶
When the Weir formula option has been selected in MIKE SHE for Overland-River exchange calculation, the overbank spilling will be calculated using the 'Villemonte formula' weir equation. The parameters below, required for this equation, must be defined for each coupling reach.
Weir coefficient¶
This parameter refers to the weir coefficient in the Villemonte formula.
Weir exponential coefficient¶
This parameter refers to the weir exponent in the Villemonte formula.
Min. upstream height above bank for full weir width¶
In the Villemonte formula, when upstream water depth above the weir approaches zero, the flow over the weir becomes undefined. To prevent numerical problems, the flow is reduced linearly to zero when the water depth is below this minimum upstream height threshold.
Allow overbank spilling from river to overland domain¶
Activate this checkbox to allow overbank spilling from the river to the overland grid cells. If left unchecked, the exchange of overland flow is only one-directional. That is, from the overland model to the river.
Min. flow area for overbank spilling¶
The minimum flow area threshold prevents overbank spilling when the river is nearly dry. The flow area is calculated by dividing the volume of water in a coupling reach by the length of the reach. If the calculated flow area is less than the specified threshold value, overbank spilling from the river to the overland flow is temporarily disabled.
Conductance¶
The conductance can be defined through three different types of exchange between surface water and aquifer (described in the technical documentation of the MIKE SHE User Manual). The available options are:
- Aquifer only
- River bed only
- Aquifer + river bed
Leakage coefficient¶
Leakage coefficient for the river bed lining (see MIKE SHE documentation). The leakage coefficient is relevant only if the conductance type is either 'Aquifer + river bed' or 'River bed only'.
Linear reservoir exchange¶
When applying the Linear Reservoir mode for Saturated Flow in MIKE SHE, exchange between the river and the baseflow can be defined individually in coupling reaches as either a Gaining river or a Losing river. That is, only one directional exchange is possible for this option.
- Gaining river: with Gaining river, the river receives water from the baseflow reservoirs in MIKE SHE
- Losing river: with Losing river, the river loses water to the baseflow reservoirs in MIKE SHE as a function of the leakage coefficient, water depth in river, bank width and length of the coupling reach.
Exchange attributes for manholes, soakaways and pipes¶
Couple to overland flow¶
Activate this check box to couple the manhole, soakaway or pipe to the overland component of MIKE SHE.
Weir coefficient¶
This parameter refers to the weir coefficient in the Villemonte formula.
Weir exponent¶
This parameter refers to the weir exponent in the Villemonte formula.
Couple to overland drainage¶
Activate this check box to couple the manhole or soakaway to the overland drainage component of MIKE SHE.
Overland drainage grid code¶
The overland drainage grid code is used for mapping MIKE SHE cells to the coupled manhole or soakaway in MIKE+. It is important to use a unique code for each coupled manhole or soakaway.
Couple to saturated zone drainage¶
Activate this check box to couple the manhole or soakaway to the saturated zone drainage component of MIKE SHE.
Saturated zone drainage grid code¶
The saturated zone drainage grid code is used for mapping MIKE SHE cells to the coupled manhole or soakaway in MIKE+. It is important to use a unique code for each coupled manhole.
Couple to saturated zone¶
Activate this check box to couple the pipe to the saturated zone component of MIKE SHE. For couplings to soakaways, this process is always active.
Conductance¶
The conductance can be defined through three different types of exchange between surface water and aquifer. The available options are:
- Link leakage + SZ conductivity
- Grouting
- Link leakage only
Leakage coefficient¶
Leakage coefficient for the pipe or the soakaway (see MIKE SHE documentation).
For couplings to pipes, the leakage coefficient is relevant only if the conductance type is either 'Link leakage + SZ conductivity ' or 'Link leakage only'.
For couplings to soakaways, the conductance type cannot be changed and is always set to 'Link leakage + SZ conductivity'.
Flooding¶
Flood area option¶
The Flood area option allows a number of cells from the MIKE SHE model to be flooded (being part of a river, lake, reservoir etc.) based on the water level from the river model. When this option is active, a river or a lake (with wide cross sections) may cause flooding of a number of cells in MIKE SHE. A cor-respondence / mapping is established between MIKE+ river h-points and individual cells in MIKE SHE. Subsequently a simple flood-mapping procedure is adopted to calculate water depths on the ground in MIKE SHE. The flood mapping procedure simply compares simulated water levels (in the corresponding h-point) with the ground level in the MIKE SHE cells. If the water level is higher than the ground level, flooding occurs.
Three options are available:
- No flooding
- Manual
- Automatic
The selected option may differ for each coupled reach. These options are described below.
No flooding¶
If the 'No flooding' option is adopted, rivers are considered lines located between adjacent cells from the MIKE SHE model. No flooding can occur and overbank spilling is not possible, even if the water level in the river rises above the elevation of the adjacent cells in MIKE SHE.
River-Overland exchange is always one way with this option, namely overland to river. If this option is used, one of the three river-aquifer exchange formulations will be adopted.
Manual¶
The manual option allows the user to delineate the potentially flooded areas, using a 2D file (.dfs2) containing code values - the flood code file specified in MIKE SHE's user interface. If the river system considered is a very complex system with a looped or meandering network, generating a complex geometry, the best result will be obtained by creating a flood code file manually by digitizing the floodplain / lake, and using this option.
Each (potentially flooded) MIKE SHE cell is linked to the nearest MIKE+'s river h-point on a coupling reach with the same flood code value. The flood code specified for each coupling reach must match the grid code in the flood code file. The flood code must be an integer.
Automatic¶
The automatic option is often useful if the geometry of rivers, lakes etc. is not too complex. This option may, for instance, be applied for wide rivers without too much meandering.
When the automatic option is chosen, MIKE SHE will automatically generate the potentially flooded areas (flood grid code map) depending on the location of the river branches and on the width and location of their cross-sections. The specified flood code is used as grid code, and the flood-mapping procedure described above is applied. Thus it is important to use unique flood codes to ensure correct mapping between MIKE+ and MIKE SHE.
Flood code¶
As described above the flood code is used for mapping MIKE SHE cells to MIKE+ rivers h-points, and for the automatic option also for generating the flood grid codes of the coupling reach. It is important to use unique flood codes to ensure correct flood-mapping.
Bed topography¶
This option controls the source of the topography used in the flooded area. It should be emphasized that the flood mapping requires a good consistency between the river cross-sections and the ground levels in MIKE SHE in order to provide relevant results.
The options are:
- Use cross sections:
- When this option is used, the ground levels of the flooded cells are substituted with values directly interpolated from the river cross sections. Notes on this option:
- This interpolation uses an inverse-distance-weighted method, using points (elevations) from the cross sections as discrete input points. When the distance between cross sections is higher than half the cell size, extra cross sections are interpolated before the cells' ground levels are interpolated.
- Please note that the ground levels are only interpolated inside the area delineated by the cross sections.
- When the Manual option is used, the user-defined flood area does not have to be identical to the area covered by the cross sections. If the Automatic option is used, the area covered by the cross sections and the flood area will always be consistent, as the flood-area is generated (automatically) based on the cross sections.
- In principle the 'Use cross sections' option ensures a good consistency between MIKE SHE ground levels and river cross sections. There will, however, often be interpolation problems related to river meandering, tributary connections, etc. where wide cross sections of different coupling reaches overlap. Thus, it is recommended to make the initial model set up using the 'Use cross sections' option and then subsequently check the resulting ground levels (“River Bed level minus Ground level in Flood Cells” in MIKE SHE Processed Data). If needed the resulting ground levels (.dfs2 file) can be used to adjust the topography grid with the modified flood coded areas (using the MIKE Zero Grid Series editor and the “Copy File into Data” command or using the “Grid Calculator” tool at the MIKE SHE Toolbox) and then used as input for a new set up, now using the 'Use grid data' option described below.
- Use grid data:
- MIKE SHE grid data is used instead of river cross sections. This option checks whether the optional bed elevation file has been specified in MIKE SHE's user interface:
- If the bed elevation file has been specified, the ground levels of the flooded cells are substituted with values from the specified .dfs2 file. The option is useful when the surface elevation data of the flood areas is more detailed than the regional terrain model.
- If the bed elevation file has not been specified, then the regional MIKE SHE surface topography is also used in flood areas. As described above, the specified .dfs2 file will often be a retrieved and modified surface topography from a previous set-up with the 'Use cross sections' option.
Bed leakage¶
As described in the technical documentation of MIKE SHE, the infiltration/seepage of MIKE SHE is calculated as ordinary exchange from the overland domain to the saturated or unsaturated zone, either using full contact or reduced contact with a specified leakage coefficient.
The bed leakage option tells whether the overland-groundwater exchange option and leakage coefficient specified in MIKE SHE's user interface should also be used in the actual flood area, or substituted by the corresponding river-aquifer conductance type and Leakage coefficient specified for the coupling reach.
The options are:
- Use grid data:
- The overland-groundwater exchange option and leakage coefficient specified in MIKE SHE's user interface is used. Both can be single value or distributed (from a .dfs2 file).
- Use river data:
- The MIKE SHE overland-groundwater exchange option and leakage coefficient in flood areas are substituted with the corresponding river-aquifer conductance type and leakage coefficient specified for the coupling reach. Please note that the two reduced contact options (‘River bed only’ and ‘Aquifer + Bed’ mentioned in MIKE SHE User Guide) lead to the same overland-groundwater exchange option.
The substitution is made in all cells from the flood area of the coupling reach.