HOI-AN project: study of erosion processes and protection measures for Hoi-An beaches
Collaborators: Nguyen Kim Dan (coordinator), Nguyen Thong (HCMUT/CARE), Nguyen Nguyet Minh (USTH/CARE), Nguyen Trung Viet (WRU), Rafael Almar (LEGOS)
Hoi An, located in central Viet Nam, around 25 kilometres south of Danang (Figure 1), is one of the most beautiful cities of Vietnam. The old town of Hoi An is listed as a UNESCO World Heritage site. Since October 2004, this well-known tourist site is under threat by severe erosion. Cua Dai Beach, north of the Thu Bon river mouth, has retreated by almost 200 m and the river channel itself has shifted south by 250 m. Several construction sites at tourist resorts were swallowed by waves, bringing work to a complete standstill. The erosion process becomes increasingly threatening, possibly for the old town itself. Current solutions for coastal erosion are temporary and would not achieve sustainable outcomes, and might in fact do the opposite.
From Tanaka et al. (2016)
A few studies (Ponsioen, 2015; Tanaka et al., 2016) have been conducted by Vietnamese, European and Japanese researchers, who proposed the following possible erosion processes at work:
There are eight hydropower plants in the upstream, starting from Ngoc Linh Mount in Quang Nam Province's Nam Tra My District. Hydropower reservoirs obstructs a huge volume of sand and mud, and thus decreases the sediment fluxes that go seaward. In addition, there is sand extraction at 15 sites along the Thu-Bon River operating at full capacity to supply materials to the building construction in the region. They largely modify the river morphology and decreases sand resources. As a consequence, sediment balance is lost in the coastal zone and the sediment flux deficit is suspected to be the primary cause of erosion of Cua-Dai Beach.
The sediment balance in the coastal zone is also relying on high-energy tides and waves, particularly during winter monsoon surges and typhoon periods. According to Huynh Cong Hoai and Le Duc Vinh (2015) the presence of the Cu-Lao Cham Island has a complex effect on the wave field and wave-induced circulation and transports in the coastal zone. What exactly is the effect of this complex and variable wave field is unknown.
- The sea level rise due to climate changes is estimated about 30 cm at the Cua-Dai Mouth; This is not believed a primary cause of the present erosion but needs to be evaluated.
However, these studies generally remain qualitative, based on aerial and satellite images of the site. Quantitative assessments and in-situ observations using numerical models are lacking, although they are needed in order to firmly endorse any of the proposed assumptions. This is what the present project is proposing. My contribution (with Nguyen Nguyet Ming as postdoc) will be to model the large scale forcing environment of the study site (waves, tides, wind-driven currents using ROMS/CROCO and WW3). Then with Thong Nguyen, circulation and sediment-transport model configurations for the nearshore zone and estuary will be setup (TELEMAC2D, ROMS/CROCO. These models will be used to expose the processes at work and test the sediment balance changes associated with changes in upstream sediment sources.