8 Water Quality and Ecosystem Modelling …
177
pumps dewatering surrounding areas and the meteorology (temperature, wind speed,
and gust, relative humidity, pressure and cloud cover). The 100 m resolution model
includes additionally a water quality module (CAEDYM) which was used to simulate
nutrients, oxygen and silica cycle, two fractions of inorganic sediments, four groups
of phytoplankton, three groups of zooplankton and three groups of fish. The model
has been validated based on hourly observed water temperature in a water profile
(9 intervals) and based on hourly measurements of the chlorophyll a. Validation of
the calculated water temperature resulted in the coefficient of determination (R
2 )
0.96 and the Nash Sutcliffe Efficiency (NSE) coefficient 0.95. For the chlorophyll,
these coefficients were lower but still satisfactory (R
2
= 0.52 and NSE = 0.51). An
example of model outputs prepared for the online presentation is shown in Fig. 8.1.
The model of higher spatial resolution was used among others for the analysis
of impacts of dredging the reservoir near to the inflow of the Vistula River. The
dredging was planned in order to restore the original geometry of the Vistula River
channel which was blocked by sediments transported with surface waters. The sediment deposition impeded water flow to the east (central part of the reservoir) and
hindered the navigation. The analysis included three scenarios: 0) current status, (1)
dredging the Vistula channel to the elevation of 253.1 m amsl. (length of the dredged
channel: 700 m; maximum depth: 1.5 m; average depth: 0.46 m). Moreover, (2)
dredging the Vistula channel to the elevation of 252.0 m amsl (length of the dredged
channel: 1470 m; maximum depth: 3.4 m; average depth: 0.87 m). In both cases, the
restored channel bottom was 40 m wide with 20 m wide slopes (Fig. 8.2). The goal
of the analysis was to assess if the planned dredging will result in increased concentrations of mineral particles and dissolved pollutants in the north-eastern part of the
reservoir, where the water intake is located, and if it results in a shorter pollutants
travel time. Such risk was considered by the operator of the reservoir, as a consequence of facilitated water flow in the direction of the water intake. Simulations
included the transport of two fractions of sediments (0.45 and 1 µm) and a virtual
tracer representing dissolved, conservative pollution. Model outputs indicated that
after the dredging, the pollutants travel time to the intake will not decrease and,
what is more, the calculated concentration of sediments in the location of intake
will be reduced (Fig. 8.3). The projected, positive effect of the dredging results from
the increased water flow velocity and water mixing rate after the restoration of the
Vistula River channel.
8.2.2 Rogo´ znik I Reservoir
The Rogo´ znik I is a relatively small, dammed reservoir (12.6 ha) located in the
municipality of Bobrowniki, in southern Poland. Maximum and average depths of
the reservoir are 2.4 and 1.28 m, respectively. Its catchment (15 km
2 ) is covered
primarily by agricultural areas and includes two other reservoirs connected in a series.
Outflow from these reservoirs represents nearly 100% of the total surface inflow to the
Rogo´ znik I. To exploit the recreational potential of the reservoir and its surroundings,
177
pumps dewatering surrounding areas and the meteorology (temperature, wind speed,
and gust, relative humidity, pressure and cloud cover). The 100 m resolution model
includes additionally a water quality module (CAEDYM) which was used to simulate
nutrients, oxygen and silica cycle, two fractions of inorganic sediments, four groups
of phytoplankton, three groups of zooplankton and three groups of fish. The model
has been validated based on hourly observed water temperature in a water profile
(9 intervals) and based on hourly measurements of the chlorophyll a. Validation of
the calculated water temperature resulted in the coefficient of determination (R
2 )
0.96 and the Nash Sutcliffe Efficiency (NSE) coefficient 0.95. For the chlorophyll,
these coefficients were lower but still satisfactory (R
2
= 0.52 and NSE = 0.51). An
example of model outputs prepared for the online presentation is shown in Fig. 8.1.
The model of higher spatial resolution was used among others for the analysis
of impacts of dredging the reservoir near to the inflow of the Vistula River. The
dredging was planned in order to restore the original geometry of the Vistula River
channel which was blocked by sediments transported with surface waters. The sediment deposition impeded water flow to the east (central part of the reservoir) and
hindered the navigation. The analysis included three scenarios: 0) current status, (1)
dredging the Vistula channel to the elevation of 253.1 m amsl. (length of the dredged
channel: 700 m; maximum depth: 1.5 m; average depth: 0.46 m). Moreover, (2)
dredging the Vistula channel to the elevation of 252.0 m amsl (length of the dredged
channel: 1470 m; maximum depth: 3.4 m; average depth: 0.87 m). In both cases, the
restored channel bottom was 40 m wide with 20 m wide slopes (Fig. 8.2). The goal
of the analysis was to assess if the planned dredging will result in increased concentrations of mineral particles and dissolved pollutants in the north-eastern part of the
reservoir, where the water intake is located, and if it results in a shorter pollutants
travel time. Such risk was considered by the operator of the reservoir, as a consequence of facilitated water flow in the direction of the water intake. Simulations
included the transport of two fractions of sediments (0.45 and 1 µm) and a virtual
tracer representing dissolved, conservative pollution. Model outputs indicated that
after the dredging, the pollutants travel time to the intake will not decrease and,
what is more, the calculated concentration of sediments in the location of intake
will be reduced (Fig. 8.3). The projected, positive effect of the dredging results from
the increased water flow velocity and water mixing rate after the restoration of the
Vistula River channel.
8.2.2 Rogo´ znik I Reservoir
The Rogo´ znik I is a relatively small, dammed reservoir (12.6 ha) located in the
municipality of Bobrowniki, in southern Poland. Maximum and average depths of
the reservoir are 2.4 and 1.28 m, respectively. Its catchment (15 km
2 ) is covered
primarily by agricultural areas and includes two other reservoirs connected in a series.
Outflow from these reservoirs represents nearly 100% of the total surface inflow to the
Rogo´ znik I. To exploit the recreational potential of the reservoir and its surroundings,