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Geo-hydrological simulation of river basin
Hydrogeios is an integrated simulation scheme, implementing a conjunctive (i.e. surface and groundwater) hydrological model that represents the soil and aquifer processes, combined with a system-oriented management scheme, which estimates the flows along the physical (i.e. hydrographic) and artificial (i.e. conveyance works) network and the actual abstractions through the hydrosystem, accounting for the properties and constraints of the hydraulic structures for the exploitation of the water resources.
The spatial scale of process representation is based on a semi-distributed schematization, to estimate the water balance at characteristic sites (i.e. nodes) of the river basin. The nodes are located along the river network (stream confluences or other control locations) and in sites where surface and groundwater abstractions are made. The description of groundwater flow field is based on a multicell delineation, thus constructing a conceptual network of interconnected tanks, whose level corresponds to the average stage of the related part of the aquifer. Finally, the water resource management system (hydrosystem) comprises a conceptual illustration of the water supply and demand locations, the major hydraulic works for the exploitation of the water resources of the basin (aqueducts, diversion projects, wells and borehole groups), and the water uses. To formulate the spatial data of the model we use the geographical information system MapWindow.
Regarding the temporal scale, the model supports monthly or daily simulation step, which is selected on the basis of the target of the study as well as the availability of hydrological inputs. The monthly step is suggested for water management studies, whereas the daily one is also suitable for the representation of flood phenomena in large basins, when the spatial rainfall data at fine temporal scales are insufficient. In the second case, to faithfully represent the propagation of flood runoff, we implement an empirical scheme for the disaggregation of the mean daily discharge through each sub-basin to finely (i.e. hourly) resolved hydrographs, which in turn are routed along the river network, by employing models of one (i.e. kinematic wave) or two (Muskingum method) parameters.
With respect to the modeling of hydrological processes at the surface, the unsaturated and the saturated soil zone, we adopt a physically-based approach, which is although as much as possible parsimonious against the number of parameters involved. The parameters are assigned to spatial units of the basin (hydrological response units) and the aquifer (zones) with similar geomorphological and hydrological characteristics; this allows disconnecting parameterization from the spatial detail of schematization. Parameters are estimated through calibration, namely by fitting the model to the observed conditions of the past. In this context, the software incorporates automatic procedures, which are based on multiple performance criteria (statistical and empirical) and advanced techniques for global and multiobjective optimization.