# Quantitative Assessment of the Environmental Impacts of Dredging and Dumping Activities at Sea
## 2 Materials and Methods  
### Description of Study Site  
The study site is located inside Quy Nhon and the Thi Nai Port, encompassing an area of 95.1 ha (Figure 1). Quy Nhon Port, 68.10 ha in surface area, belongs to the Hai Cang commune. Its eastern boundary is adjacent to vessels operating at the port, Dong Da Port is to the west, boat shelters are located at the Thi Nai lagoon in the south. Quy Nhon Port is one of the ten largest ports in Viet Nam and serves vessels that can load up to 30,000 tons with the regular operating frequency, and the port capacity is 10 million tons per year. The dredging and maintenance requirements of Quy Nhon Port play an important role in the transportation, evaluation, and selection of dredging location and dredging volume. The dredging area is 7.6 km from the port, 4.6 km from Hai Giang seashore, and 8.7 km from the Ghenh Rang tourist attraction (Figure 1). The water depth at the dredging position is approximately \(-\)28 m to \(-\)30 m.  
A dredger boat was used to dredge the bed surrounding the port. The spoils are transported by means of a hopper barge with a bottom discharge. The spoils can be dumped at sea by opening the floor of the barge, minimizing the diffusion of these materials in water and the turbidity of the ocean, thereby reducing the negative effects on the surrounding ecological environment. The impacts of discharge on the surrounding environment were evaluated using a combination of spectral wind-wave and 2D flow model, the mud transport module and the particle tracking module. The momentum equation in the x-direction is as follows:  
\[\frac{\partial p}{\partial t}+\frac{\partial}{\partial x}\Big{(}\frac{p^{2}}{h} \Big{)}+\frac{\partial}{\partial y}\Big{(}\frac{pq}{h}\Big{)}+gh\frac{\partial \bar{c}}{\partial x}+\frac{gp\sqrt{p^{2}+q^{2}}}{C^{2}\cdot h^{2}}-\frac{1}{ \rho_{w}}\Big{[}\frac{\partial}{\partial x}(h\tau_{xx})+\frac{\partial}{ \partial y}\Big{(}h\tau_{yy}\Big{)}\Big{]}-\Omega_{q}-fVV_{x}+\frac{h}{\rho_{w }}\frac{\partial}{\partial x}(p_{a})=0 \tag{3}\]  
The momentum equation in the y-direction is as follows:  
\[\frac{\partial q}{\partial t}+\frac{\partial}{\partial y}\Big{(}\frac{\vec{x }^{2}}{h}\Big{)}+\frac{\partial}{\partial x}\Big{(}\frac{pq}{h}\Big{)}+gh \frac{\partial\bar{c}}{\partial y}+\frac{gp\sqrt{p^{2}+q^{2}}}{C^{2}\cdot h^{2 }}-\frac{1}{\rho_{w}}\Big{[}\frac{\partial}{\partial y}\Big{(}h\tau_{yy} \Big{)}+\frac{\partial}{\partial x}\Big{(}h\tau_{xy}\Big{)}\Big{]}-\Omega_{q} -fVV_{y}+\frac{h}{\rho_{w}}\frac{\partial}{\partial xy}(p_{a})=0 \tag{4}\]  
where \(p\) and \(q\) (m\({}^{3}\)/s/m) are the fluxes in the x- and y-directions, respectively; \(t\) (\(s\)) is the time, \(x\) and \(y\) (m) are the Cartesian coordinates; \(h\) (m) is the water depth; \(d\) is the time-varying water depth (m); \(g\) (9.81 m/s\({}^{2}\)) is the acceleration due to gravity; \(\zeta\) (m) is the sea surface elevation; \(C\) is a Chezy resistance parameter (m\({}^{1/2}\)/s);\(f(V)\) is the wind friction factor; \(V\), \(V_{x}\), and \(V_{y}\) are the wind speed and its components in the x- and y-directions (m/s), respectively; \(\Omega\) is the Coriolis parameter, which is latitude dependent(s\({}^{-1}\)); \(Pa\) is the atmospheric pressure (kg/m/s\({}^{2}\)); \(\rho_{w}\) is the density of water (kg/m\({}^{3}\)); and \(\tau_{xx}\), \(\tau_{xy}\), \(\tau_{yy}\) are the components of effective shear stress. Sediment transport formulations are built into advection-dispersion module, 2D-AD.