A

review by Alongi (2008) concluded that tsunami wave flow pressure was significantly reduced when the mangrove forest was 100 m wide. The wave energy spectrum and wave power are dissipated within a mangrove forest even over a small distance (Vo-Luong & Massel 2008). The magnitude of the energy absorbed depends strongly on the mangrove structures (e.g. density, stem and root diameter, shore slope) and the spectral characteristics of incident waves (Massel et al. 1999, Alongi 2008). The dissipation of wave energy check details inside mangrove forests is caused mostly by wave-trunk interactions and wave breaking (Vo-Luong & Massel 2006). Mazda et al. (1997a) in their study in the Red River Delta, Vietnam, showed that wave reduction due to drag force on the trees is significant in high density, six-year-old mangrove forests. The hydrodynamics of mangrove swamps changes over a wide range, depending on their species, density and tidal condition (Mazda et al. 1997b).

The high tree density and the overground roots in a mangrove forest present a much higher drag force to incoming waves than the bare sandy surface of a mudflat does. The wave drag force can be expressed as an exponential function (Quartel et al. 2007). The general objective of this paper is to analyse the relationship between wave height and mangrove forest structures, and then to define minimum mangrove forest band width for coastal protection from waves for the coastline of Vietnam. The study was conducted in two coastal mangrove forests of Vietnam. The northern study site is located in the delta (the Linsitinib price second largest in Vietnam) of the Red River, which flows into the Bay of Tonkin (Figure 1). Tides in the Bay of Tonkin are diurnal

with a range of 2.6–3.2 m. Active intertidal mudflats, mangrove swamps and supratidal marshes in estuaries and along open coastlines characterize the coastal areas (Mathers & Zalesiewicz 1999, Quartel et al. 2007). The mangroves in the Red River delta are one of the main remaining large tracts of mangrove forest in Vietnam, which are important sites for breeding/stopover along the East-Asian or Australian flyways. In this northern region, four mangrove locations were selected for the research: Tien Lang, Cat Ba–Hai Coproporphyrinogen III oxidase Phong, Hoang Tan– Quang Ninh and Tien Hai–Thai Binh. In each location, four mangrove forest plots were set up to measure mangrove structure and wave height at different cross-shore distances. The southern study site is the Can Gio mangrove forest. The first Biosphere Reserve in Vietnam, it is located 40 km southeast of Ho Chi Minh City and has a total area of 75 740 ha (Figure 1). Can Gio lies in a recently formed, soft, silty delta with an irregular, semi-diurnal tidal regime (Vo-Luong & Massel 2006). The major habitat types in Can Gio are plantation mangroves, of which there are about 20 000 ha, and naturally regenerating mangroves.