MIKE Hydro River network limitations

There are a few features of MIKE Hydro River that do not relate well to MIKE SHE.

Short branches

In MIKE Hydro River there is no restriction on how short your branches are. If you are trying to simulate discontuous lakes or structures on the flood plain, for example. you may have very short branches. However, MIKE SHE does not allow MIKE Hydro River branches to be shorter than the cell size. Gener­ally, though, short branches are a sign that you should probably reconsider your model conceptualization - or switch to MIKE FLOOD, which allows flood plain structures.

Parallel branches

Like short branches, MIKE SHE does not like it when your branches are too close together. If you have parallel branches that are too close together, then the branches may be mapped to the same river link. However, each river link must be mapped to a unique branch. As a rule of thumb, parallel branches should be greater than a cell width apart. However, this is not uniformly true, since the two close parallel branches may map onto opposite sides of a cell, if they are located on either side of a cell mid-point. Thus, you may have unex­pected problems, if you change the cell size in a model that was working and you have branches that are closer together than one cell size.

Long coupling links

MIKE SHE links to MIKE Hydro River branches. However, when two branches are connected, water is passed between the branches directly. The link has not physical length or storage itself. If your links are too long, there will be an error in the timing of the flows between the two branches. So, the links should be kept short. MIKE Hydro River does not have any restrictions on how long the links can be, but MIKE SHE will issue a warning if the links are longer than a cell size. The warning is simply to informing you that there is no possibility for groundwater-surface water exchange in the link.

Long distances between cross sections

MIKE Hydro River controls the distance between the calculation nodes. The properties at the calculation nodes are linearly interpolated from the available cross-sections. This includes geometric properties such as bank and bottom elevations, marker locations, etc. However, linear interpolation can easily result in inconsistencies between elevations in MIKE SHE.and marker eleva­tions in MIKE Hydro River. If the bank elevation is higher than the topography, then overland flow into the river will be restricted. If the downstream river bot­tom elevation is higher than the side branch bottom elevation, then MIKE Hydro River will likely be unstable.

Long distances between calculation nodes

This is not the same as long distances between cross-sections. MIKE Hydro River manages the water at the q-points directly linked to the river links. MIKE SHE and the river link system automatically interpolates the nearest river link. However, if the calculation nodes are very far apart or very close together, then the linear interpolation of water volumes between the calculation points may lead to discrepancies in the available water volumes especially if the river links are being used for irrigation or the river is losing water. In this sense, the distance between the calculation nodes, should be similar to the MIKE SHE grid spacing.