Aveneu Park, Starling, Australia

2.1 steady state model that can be applied when

2.1 QUAL2Kw

QUAL2Kw is a modelling framework
with an aim to delineate a modernized version of U.S Environmental Protection
Agency’s standard river water quality model: QUAL2E (Brown and Barnwell, 1987;
Pelletier et al., 2006). QUAL2E was followed by QUAL2EU that had several
limitations. In 2002, QUAL2K was developed identifying the various limitations
in QUAL2E and QUAL2EU that included the expansion of computational structure
and addition of new constituent interactions, such as algal BOD,
denitrification, and DO change caused by fixed plant (Park and Lee, 2002).

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This was followed by
QUAL2Kw, which was developed by Greg Pelletier and Steve Chapra to simulate
water quality in streams and rivers, with certain modifications to QUAL2K
(Vieira et al., 2013). It is a one dimensional steady state model that can be
applied when the flow and pollution load into the river remains approximately
constant (Oliveira et al., 2012). The model can simulate a number of
constituents including temperature, pH, carbonaceous biochemical demand,
sediment oxygen demand, dissolved oxygen, organic nitrogen, ammonia nitrogen,
nitrite and nitrate nitrogen, organic and inorganic phosphorous, total
nitrogen, total phosphorous, phytoplankton and bottom algae. Based on the flow
condition, the user can choose between permanent or dynamic flow conditions
(Camargo et al., 2010). Other than this, major input data included are
geometric properties of river like slope, channel width, side slope and
Manning’s roughness co-efficient, flow rate, pollutant loads and meteorological
parameters (Pelletier and Chapra,2008; Oliveira et al 2012). The river can be
simulated as collection of reaches (equal or unequal lengths) and tributaries
considered as point sources (Sharma and Kansal, 2013).

A general mass balance
(excluding hyporheic exchange) for a constituent concentration (Ci)
in the water column of a reach can be expressed as:

Where Qi = flow at reach (m3/d),
Qab,I = abstraction flow
at reach i (m/d), Vi =
volume of reach i (m3), Wi
= the external loading of the constituent to reach i (mg/day), Si = sources and sinks of the
constituent due to reactions and mass transfer mechanisms (mg/m3/day),
E’I = bulk
dispersion co-efficient between reaches i and i+1 (m3/day),

E’i-1 is the bulk dispersion
coefficients between reaches i-1 and I (m/day). Figure 1 represents the
simplified diagram of interacting water quality state variables.

 

Figure 1: Mass balance
for constituents in a reach segment “I”

 

The model has two
distinguishable features. First, internal simulation of sediment-water fluxes
of dissolved oxygen and nutrients. Here, the oxygen and nutrient fluxes are
computed as a function of settling particulate organic matter, reactions
occurring within sediments, and the soluble form concentration on overlying
waters. Second, the hyporheic zone is modelled. This is the area below the
stream bed where water percolates through spaces between the rocks and cobbles.
This is another important factor to be considered while simulating shallow
streams (Pelletier et al., 2006).

QUAL series have been
widely used in river water quality monitoring on various rivers. Application of
automated QUAL2Kw for simulating various water quality management strategies
during critical period to maintain the targeted water quality criteria was
analysed for Bagmati River, Nepal (Kannel et al., 2007).  QUAL2Kw was also applied to predict the
impact of flow conditions, discharges and tributaries on the water quality of
Lis River, Portugal (Vieira et al.,2013). It has been used in water quality
simulation of Certima River, Portugal (Oliveria et al., 2012) Brazil’s Fidalgo
watershed (Camargo et al., 2010) and River Karanja, India (Kori et al., 2013).
The QUAL series was applied for river water quality monitoring on Nakdong
River, Korea (Park and Lee, 2002) Kali River, India (Ghosh et al., 1996) and
Yamuna River, India (Paliwal et al., 2007). 

2.2 MIKE 11

MIKE 11 is a
user-friendly, fully dynamic, one-dimensional modelling tool for the detailed
analysis, design, management and operations of both simple and complex river
and channel systems, developed by Danish Hydraulic Institute (DHI) (DHI,2003).
It is a software package used for flow simulation, water quality assessment and
sediment transport in irrigation systems, rivers, estuaries, channels and other water bodies (Gu et al., 2015). The model
is intended to perform detailed modelling of rivers, including special
treatment of floodplains, road overtopping, gate openings, culverts and weirs
(Kamel, 2008). MIKE11 comprised of several modules namely rainfall-runoff (RR),
hydrodynamic (HD), advection-dispersion (AD) which can be used in combination
or as stand-alone simulators. MIKE 11-NAM is a rainfall-runoff model that is
part of the MIKE 11- RR module (Doulgeris et al., 2011). The hydrodynamic
module (HD) forms the core of MIKE 11 modelling system and is the basis for
most modules including Flood Forecasting, AD, water quality and sediment
transport modules (Gu et al.,2016). The MIKE 11- HD is a module used for
computing unsteady flow, discharge and water level in rivers and channels that
are based on Saint- Venant equations and is as follows:

(2)

(3)

Where Q
and A are the discharge (m3/s)
and the cross-sectional flow area (m2) respectively, q is the lateral inflow (m3/s),
h is the water level above a
reference datum (m), x is downstream
direction (m), t is time (s), n is the Manning resistance co-efficient
(m-1/3.s), R is the
hydraulic or resistance radius (m), g
is the acceleration due to gravity (m2/s) and ? is the momentum distribution co-efficient introduced to account
for the non-uniform vertical distribution of velocity in a given section .The
solutions to the above equations are based on the following assumptions (Kamel,
2008):

·        
The water is
incompressible and homogeneous (i.e. negligible variation in density).

·        
The bottom slope is
small, thus the cosine of the angle it makes with the horizontal may be taken
as 1.

·        
The wavelengths are
large compared to the water depth, assuming that the flow everywhere can be
assumed to flow parallel to the bottom (i.e. vertical accelerations can be
ignored, and a hydrostatic pressure variation in the vertical direction can be
assumed).

·        
The flow is
sub-critical (a super-critical flow is modelled in MIKE 11, however, more
restrictive conditions are applied).

MIKE 11 has been widely
used by researchers for the water quality assessment of rivers and lakes. MIKE
11 model was used to evaluate water quality management plans on river basin of
Beijing, China; for which Lao Hewen river was considered. Along with MIKE 11-
HD and MIKE-11 AD, ECOlab was used. ECOlab is a dimensionless ecological process
toolbox that forms the basis of the water quality simulation which requires HD
and AD inputs. It is an extended version of transport-dispersion module, used
to simulate the reaction processes of multi-compound systems, modelling of
variety of biochemical interaction processes including BOD and DO computations
and simulation of nutrients, macrophytes and plankton. It has been majorly used
in water quality simulation (Liang et al., 2015). Gu et al. used integrated
MIKE 11 water quality model to understand the water environment of the ten
primary rivers crossing the Qinhuangdao coastal water. Model was first
calibrated with the field measured chemical oxygen demand (COD) concentrations.
It was concluded that MIKE 11 constituting MIKE 11- HD and MIKE 11-AD successfully
calibrated and was applied to manage and understand the water environment of
rivers into the Qinhuangdao coastal water. Along with this, positions of long
term river pollutant monitoring stations for ten rivers were suggested. (Gu et
al., 2016). MIKE 11-HD was applied on the Euphrates River in Iraq to study the
unsteady flow simulations along the stream channel reach for a stream length of
1.6km. A particular reach wherein, a particular cross- section was considered,
and MIKE 11 was compared with Uday model for their observed and estimated stage
hydrographs. Results showed that, with limited available data, MIKE 11 provided
better results (Kamel, 2008). MIKE 11 modelling system was used for surface
water simulation of Strymonas River catchment. MIKE 11-NAM was used for
rainfall-runoff simulation and MIKE 11-HD for unsteady flow simulation of River
Strymonas and Lake Kerkini (Doulgeris et al., 2011). MIKE-11 NAM along with
MIKE SHE and WATBAL was applied on three catchments on Zimbabwe, for model validation
and comparison. It was observed that all models gave good results for at-least
one year’s data for calibration (Refsgaard and Knudsen, 1996). MIKE 21-HD was
applied for coastal water quality monitoring and modelling of Adyar, Cooum Rivers
and Ennore creek and ports nearby, off Chennai city. Sampling locations being
30, the water samples were collected on monthly basis and monitored for a
number of parameters. The model simulated the water level and current flow
pattern (Mishra et al., 2015). The limitations of MIKE 11 model is 1) requires
large amount of data, causing difficulty in simulating some parameters with
simple descriptions 2) cross-sections of channels at reach boundaries is needed
which makes the calibration and evaluation of results a complicated task for
user (Cox, 2003).

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