All of the upper branches of the river Madeira find their way to the falls across the open, almost level Mojos and Beni plains, of which are yearly flooded to an average depth of about for a period of from three to four months. From its source in the confluence of Madre de Dios and Mamoré rivers and downstream to Abuna river the Madeira flows northward forming border between Bolivia and Brazil. Below its confluence with the latter tributary the flow of river changes to north-eastward direction, inland of Rondônia state of Brazil. The section of the river from the border to Porto Velho has notable drop of bed and was not navigable. Before 2012 the falls of Teotônio and of San Antonio existed here, they had higher flow rate and bigger level drop than more famous Boyoma Falls in Africa. Currently these rapids are submerged by the reservoir of Santo Antônio Dam. Below Porto Velho the Madeira meanders north-eastward through the Rondônia and Amazonas states of north west Brazil to its junction with the Amazon. The Rio Madeira Sustainable Development Reserve, created in 2006, extends along the north bank of the river opposite the town of Novo Aripuanã. At its mouth is Ilha Tupinambaranas, an extensive marshy region formed by the Madeira's distributaries. The Madeira river rises more than 15 m (50 ft) during the rainy season, and ocean vessels may ascend it to the Falls of San Antonio, near Porto Velho, Brazil, above its mouth; but in the dry months, from June to November, it is only navigable for the same distance for craft drawing about of water. The Madeira-Mamoré Railroad runs in a loop around the unnavigable section to Guajará-Mirim on the Mamoré River, but is not functional, limiting shipping from the Atlantic at Porto Velho. Today, it is also one of the Amazon Basin's most active waterways, and helps export close to four million tons of grains, which are loaded onto barges in Porto Velho, where both Cargill and Amaggi have loading facilities, and then shipped down the Madeira to the ports of Itacoatiara, near the mouth of the Madeira, just upstream on the left bank of the Amazon, or further down the Amazon, to the port of Santarem, at the mouth of the Tapajos River.