Decision Support System for Biebrza National Park - Efficient Decision Support Systems: Practice and Challenges from Current to Future - page 447

particular stretches of the Biebrza Valley. Results of selected modeling approaches were
included in the DSS and applied in habitat contiguity and evolution analysis.
6.1 Soligenic mires models structure
To quantify groundwater discharge as a crucial factor for the functioning of groundwater
fed mires, the MODFLOW model (McDonald & Harbaugh, 1988) was applied in two
separate set-ups: in the Upper Basin (Batelaan & Kuntohadi, 2002; Van Loon et al. , 2010) and
in the Middle Basin (Okruszko, 2005; Grygoruk et al. , 2011). Results of the modeling were
analyzed due to habitat contiguity in conditions of various hydrological flow processes and
fluxes in the peat soils. Both approaches pay significant attention to groundwater discharge
mapping, the crucial factor for the functioning of throughflow mires and their evolution.
Groundwater models compute continuous groundwater levels. Applied packages
(especially the MODFLOW Drain and Seepage Packages) allowed also to interpret
groundwater discharge spatial distribution patterns.
6.2 Fluviogenic wetlands models structure
The state of fluviogenic (riparian) ecosystems is dependent mostly on the conditions of their
hydrological alimentation by flooding waters. The most important hydrological
characteristics, conditioning of the growth and the development of swamp vegetation, are:
inundation surface, mean inundation depth, the frequency and the duration of inundation.
A hydrodynamic model coupled with GIS techniques makes it possible to obtain necessary
data for the determination of the above-mentioned hydrological characteristics. It is also a
tool which facilitates the estimation of the influence of different river valley management
methods on hydraulic conditions of water flow. It can even be used as a research tool for
executing effective policy of natural values protection within the Biebrza National Park.
Unsteady flow in natural rivers is usually treated as a one-dimensional flow in practice and
is based on St Venant equations. In order to simulate flood flow in the lower Biebrza Basin,
the one-dimensional unsteady model flow RIVER-SV was applied (Swiatek, 2007). The basic
form of the non-linear St Venant equations combined with retention effects of the vegetated
areas on flood wave conveyance were used in the model.
The model uses the Darcy-Weisbach relationship for the description of flow rules. It also
enables introduction of water mass and momentum exchange processes between the main
channel and floodplains, and it has the flexibility to account for parts of a cross section
covered with vegetation and those with no vegetation. Thus, the developed model enables
accounting for unsteady flow and flow resistance resulting from both vegetation covering a
cross section and momentum exchange between the main channel and floodplains.
In the topological discretization scheme of the flow, the Lower Biebrza Basin and its
floodplain are represented as a one - dimensional channel from Osowiec gauge to Burzyn
gauge. The Wissa River (a tributary) is treated as a point lateral inflow and described by the
flow hydrograph at the Czachy gauge. Geometry of the river channel and floodplain is
described by 47 river cross sections. The cross sections were measured by manual sounding
for the main channel part and the topography of the floodplain was calculated from the
Digital Elevation Model. Field monitoring in the Lower Biebrza Basin proves that during
flood periods, the river valley consists of parts which mainly act as storage for flood water
and of active flow areas (Chormanski and Miroslaw-Swiatek 2006). The 1D model is capable
of describing flood conditions using the appropriate geometry of cross-sections, which are
limited to the active flow zones. In the developed model, the particular areas for each cross-