The MIKE Hydro River (HD) hydraulic model uses the precise cross-sections, as defined in the cross-section file, for calculating the river water levels and the river volumes. However, the exchange of water between MIKE Hydro River and MIKE SHE is calculated based the river-link cross-section.
The river-link uses a simplified, triangular cross-section interpolated (distance weighted) from the two nearest MIKE Hydro River cross-sections. The top width is equal to the distance between the cross-section’s left and right bank markers. The elevation of the bottom of the triangle equals the lowest depth of the MIKE Hydro River cross-section (the elevation of Marker 2 in the cross-section). The left and right bank elevations in MIKE Hydro River (cross-section markers 1 and 3 in MIKE Hydro River) are used to define the left and right bank elevations of the river link (See Figure 27.2).
Figure 27.2 A typical simplified MIKE SHE river link cross-section compared to the equivalent MIKE Hydro River cross-section
If the MIKE Hydro River cross-section is wider than the MIKE SHE cell size, then the river-link cross-section is reduced to the cell width.This is a very important limitation, as it embodies the assumption that the river is narrower than the MIKE SHE cell width. If your river is wider than a cell width, and you want to simulate water on the flood plain, then you will need to use either the Flooding from MIKE Hydro River to MIKE SHE using Flood Codes (V1 p. 537) option or the Direct Overbank Spilling to and from MIKE Hydro River (V1 p. 539) option.
If you don’t want to simulate flooding, then the reduction of the river link width to the cell width will not likely cause a problem, as MIKE SHE assumes that the primary exchange between the river and the aquifer takes place through the river banks. For more detail on the river aquifer exchange see Groundwater exchange with MIKE Hydro River (V1 p. 531).
For more detail on flooding and overland exchange with MIKE Hydro River see Overland Flow Exchange with MIKE Hydro River (V1 p. 536)
