4. Conclusions
In this study, SS estimation equation and RPI package were
embedded into the WASP model to assist the river water quality
simulation of the Kaoping River. A direct linkage between the RPI
calculation and the WASP model was developed to obtain an
immediate water quality evaluation. The major findings of this
study include the following:
(1) Water quality monitoring results indicate that SS played an
important role in RPI calculation and SS was a critical factor
during the RPI calculation especially for the upper catchment
in wet seasons. This was due to the fact that the soil
erosion caused the increase in the SS concentrations after
storms.
(2) In the wet seasons, higher river flow rates caused the discharges
of NPS pollutants (NH3–N and SS) into the upper
sections of the river. Higher river flow rates also caused
the turbulence of the flow and increase in DO concentrations
in the upper section of the river. Thus, NH3–N and DO
affected the RPI value in the upper sections of the river.
(3) SS concentrations were highly correlated with the flow rates
of the Kaoping River. The obtained SS and flow rate equations
were as follows: Y = 0.028X 0.37 for low flow rate
(flow rate: 0–50 m3/s), Y = 0.13X 21.36 for high flow rate
(flow rate: 50–650 m3/s) (Y = flow rate, m3/s; X = SS concentration,
mg/L). The equations were embedded in the integrated
WASP modeling for SS simulation to obtain more
representative SS data and RPI values
(4) During the evaluation, water quality outputs from the WASP
modeling were used for RPI calculation. Thus, an integral
decision-making system combining SS estimation equation,
RPI package, and water quality model for river water quality
evaluation was developed.
(5) This study demonstrates that the introduction of SS estimation
equation and RPI package into WASP simulation has
been shown to be a significant advance in estimating water
quality in Kaoping River. The developed decision-making
modeling concept could be easily adopted to other similar
rivers. Thus, WASP modeling assisted RPI estimation provides
a good tool to effectively simulate the impacts of pollution
on river water quality. The integrated system will be
useful in developing appropriate water quality management
strategies for the improvement of river water quality, and
this makes it easier for decision-makers to evaluate alternative
water quality management plans.