# Quantitative Assessment of the Environmental Impacts of Dredging and Dumping Activities at Sea
## 1 Introduction  
Dredging is a crucial activity, regularly carried out to maintain safe passage for boats and ships at ports and harbors [1; 2; 3; 4; 5; 6]. In another sense, dredging is important for maintaining harbor operations, i.e., importing and exporting goods. However, the disposal of dredged spoil at sea can potentially affect the marine environment and its ecosystems [7; 8]. The dredging and dumping of spoils at sea inevitably increase the turbidity levels and settlement of fine sediment over an extended area [9; 10]. This can propagate to a large area around the dumped location [11; 12; 13; 14; 15; 16; 17; 18]. The dumping of spoils can lead to the smothering of the seabed environment, coral reefs, egg-laying nests of fish and can disturb their navigations [19; 20; 21]. Finally, dredging and dumping change the topography of the seabed at both the dredging and dumping locations and therefore, can change local flow patterns [22]. As a result, dredging and its related activities should be monitored, controlled and their impacts on the marine environments should be evaluated [23].  
The Qui Nhon Port is one of the largest international ports in Central Viet Nam, with a capability to berth ships up to 30,000 tons at the regular operating frequency [24]. The port serves for the exchange of goods between Binh Dinh Province and the Central and Central Highland Viet Nam, as well as forCambodia, Laos, and Thailand. To maintain navigation, dredging is usually carried out twice per year. Existing considerations are the method of dredging and location of suitable locations to dump the spoils without adversely affecting the surrounding environment. Diggers are used to dredge the port area. The dredged spoils are transported in hopper barges that open at the bottom. The barges have specialized designs and are typically used for transporting and disposing of dredged materials, in order to ensure environmental protection in a cost-effective manner. In particular, this method can minimize the diffusion of dredged materials and limit the increased turbidity in seawater. In this manner, it can minimize the impacts on the surrounding ecological environment.  
To evaluate the effect of dredging and dumping activities on the marine environment, previous studies have mostly used two- and three-dimensional models [25; 26; 27; 28; 29; 30; 31; 32] based on field data, calibration and validation for realistic assessment of the physical process and simulation of the sediment dispersion of the bed load movement of the dredged materials near the port [33; 34; 35; 36; 37; 38; 39; 40; 41]. This study combines the two-dimensional (2D) numerical approach (using MIKE 21) with numerical weather predictions (Global Forecast System (GFS) model) and is a new modeling approach for the assessment of dredging and dumping activities in Viet Nam. The study develops a two-dimensional hydrodynamic advection-diffusion model to simulate the propagation of contaminants in dredged materials to the sea with the assumption that the total volume of dredged materials from Quy Nhon port is transported by barges to the dumping location. The principal objective was to assess the impacts of dredging and dumping using a hybrid modeling approach (numerical weather prediction and hydrodynamics). The aims of this study were (1) the simulation of wind-wave propagation from offshore to the study area using wind data from the GFS global model in a 2D model, (2) the validation and calibration of wave height in a 2D model, (3) the validation and calibration of the hydraulics using the 2D model, (4) the simulation of the sediment transport process in a 2D mud transport (MT) model, and (5) the simulation of the diffusion of materials at the dumping location in a 2D particle tracking (PT) model.