Minho River basin covers a total area of 17 080 km2, which of them – 900 km2 – in Portugal (about 5%). The basin is north and west limited by the Spanish basins of Ulla, Tambre, Mandeo, Eume, Masma, Eo, Navia and Narcea Rivers, at East and South by basins of Douro, Lima and Âncora Rivers.
Minho River rises in Spain, in Meira Moutain and has an extension of 300 km– from which about 70 km are located in Portugal - until reaching the estuary. The limit of tide penetration may reach 35 km ahead Valença do Minho (Vila et al., 1984). The river has a considerable annual average flow rate of 242 m3/s and a pronounced seasonal variability.
Minho estuary - located 41º 55’ 08’’ North and 8º 46’ 26’’ West - has a total area of 3.4 km2, including Coura estuary. Minho estuary, represented in Figure 1 , has a maximum width of 3 km and is narrower at its mouth close to Santa Tegra mount. The estuary maximum depth is about 4m near the mouth. At the mouth, Insua Island splits the flow into two channels. Secondary effluents into Minho Estuary are Coura River and Tamuxe River. Tamuxe River extends over 14 km, to reach Minho estuary – about 3km from the estuary mouth. This river has a flow rate of 10 m3/s during the wet season. Coura River extends over 10 km, reaching the estuary 2 km before the estuary mouth and has an annual average flow rate of 12 m3/s.
Figure 1 - River Minho Estuary.