Sado river, Portugal Location The Sado River is located in the southwest of Portugal and it is the largest river that entirely flows in the Portuguese territory. The river originates at the south of the basin, in the Vigia mountain. The river flows initially from south to north (which is very unusual in Portugal) and subsequently turns west, towards the Atlantic Ocean. There are two major cities in the basin: Setúbal, located in the estuary, about 35 km south of Lisbon (the capital of Portugal), and Alcácer do Sal, about 40 km south of Setúbal (approx. 64,000 and 15,000 inhabitants, respectively). The tidal limit is ca. 20 km upstream Alcácer do Sal. Lisbon Atlantic Ocean Setúbal Alcácer do Sal Sado River Spain Catchment description The economic sectors in the basin are distributed roughly as follows: 15 % primary, 30 % secondary, and 55 % tertiary. The main use of the land is non-irrigated agricultural. Atlantic Ocean The maximum altitude of the basin is 230 m. The length of the river, its average slope and the basin area are 180 km, 1,5º/ 00 and 7 640 km 2. The basin is essentially a sedimentary cenozoic basin. There are numerous areas of conservation value and the endogenous ichthyofauna is mainly Rutilus alburnoides, and the introduced Anguilla anguilla. The Sado River estuary is also known for its important population of dauphins. Around 2001, the river basin plans for the major Portuguese rivers, including the Sado River, were accomplished, providing a very comprehensive and integrated characterization of the basins regarding all the water related issues, such as the physical systems and the ecosystems, and the economic and the legal systems. Key descriptors Basin area at the monitoring section 2713 km 2 Start of the rainfall and flow measurements 1933/1934 Mean annual rainfall 650 mm Mean annual runoff 91 mm Modulus of flow 7.8 m 3 s -1 Highest instantaneous peak flow and date 2008 m 3 s -1, Dec 1949 Lowest daily mean flow 0.0 m 3 s -1 (in dry years)
Hydrological summary Hydrological Observatory description According to the characterization carried out in the Sado River basin plan, the mean annual rainfall in the Sado River basin for the period between 1941/42 and 1990/91 was estimated at 621 mm, from which only 175 mm is surface runoff (mean annual flow volume of ca. 1350 hm³). Figure. Sado River basin. Mean annual rainfall (mm). Figure. Sado River basin. Mean annual flow (mm).
Within the years and among years, the flow regime is very irregular being characterized by several months with very low flows or even without any flow. The number of months without flow in some small river basins may reach up to 3 months. There are several dams located in the basin (mainly in tributaries of Sado River) which provide storage capacities for urban supply and for irrigation purposes. The most important dams are the following ones (between brackets, the name of the stream, the watershed area, if available, and the year in which the exploitation started): - Alvito (Odivelas water stream, 212 km 2, 1977); - Odivelas (Odivelas water stream, 1972); - Campilhas (Campilhas water stream, 109 km 2, 1954); - Fonte Serne (Benatelar water stream, 30 km 2, 1976); - Monte da Rocha (Sado River, 1972); - Pego do Altar (Santa Catarina water stream, 743 km 2, 1949); - Roxo (Roxo water stream, 351 km 2, 1967); - Vale do Gaio (Xarrama water stream, 509 km 2, 1949) The storage capacity created by the previous dams is approximately 220 hm³/year, that is to say, only about 16 % of the available water resources. Due the locations of the dams and to their relatively small storage capacities the flows in the basin can be considered as approximately representing the natural regime. However, effluent returns from waste water treatment facilities are significant in some river reaches.
Figure. Sado River basin. Main dams. Data availability Most of the rainfall and flow data are in the public domain and available in the internet. Supporting data e.g. describing geology, soils, elevation, and land use, are also available, namely in the Sado River basin plan. Facilities The Instituto da Água, IA (which is the water authority in Portugal), undertakes flow monitoring at a large number of sites within Sado River basin, with the longest series of records starting in the early 1930s. According to the IA there are 39 stream gage stations in Sado River basin, from which a significant number is presently inactive. Only 14 stations have flow records, most of them during very short recording periods. From those 14 stations, 3 are located in the Sado River, one of them presently deactivated. The IA also maintains a network of water quality monitoring stations within the catchment. Other meteorological data, besides rainfall, are collected by the IA and also by Portuguese Meteorological Institute.
Figure. Sado River basin. Flow monitoring network: quantity (left side) and quality (right side).
Table. Sado River basin. Annual flow records at the stream gauging stations. Taking into account that Moinho da Gamitinha stream gauging station dominates a significant portion of the upstream basin of Sado River, also receiving water from São Domingos, Campilhas,
and the Roxo rivers, and that it has a considerable long recording period it could become part of an observatory system. Figure. Schematic location of Moinho da Gamitinha stream gauging station. Value to network The Sado Observatory provides data for hydrological conditions that are common in its region but which are quite different from those monitored by many other observatories in the network. Some important distinguishing features of the Sado catchment in the European context are: The large size of the basin, long time series, the low area specific runoff, and the long periods without flow in certain subbasins. Contact for further information Joao Hipolito, CEHIDRO/IST, jh@civil.ist.utl.pt Manuela Portela, CEHIDRO/IST, mps@civil.ist.utl.pt Links for the download of Sado River basin plan: http://www.ccdr-a.gov.pt/app/pbhsado/