In a linear reservoir model, groundwater discharge, i.e., flux through the outlet(s) is proportional to the water level, and because catchment area is constant, it is also proportional to the storage. Specifically, the coupled differential equations solved are:
(A.1.1)
(A.1.2) 
where the variables related to the geometry (h and L) and time constants k are defined in Fig A.1.1. The dimensions of L and h are [Length].
Fig A.1.1 The geometry of the linear reservoir model
The mathematical solution of the linear reservoir equations in MIKE HYDRO is also valid for situations where the groundwater storage is emptied (when outflows permanently exceed inflows), or when overflow occurs (when inflows permanently exceed outflows). This is also valid when the deep groundwater level reaches the shallow outlet, causing flow back into the shallow reservoir.
