Saudi drainage basins and their outlets: 2,359 basins and 354,737 km of wadis, with where each basin drains

2,359 drainage basins with their area inside the country, the elevation of their lowest point, and an explicit class for where the water goes: to the sea, across the border, or into a closed depression where it ends.

With the full wadi network (40,056 segments, 354,737 km) carrying a Strahler order, and a collection point per basin. 82.5% of basin area drains to closed depressions and 14.3% to the sea.

Who it is for

Water and dam authorities, flood and stormwater studies, physical geography departments, engineering consultancies and postgraduate students.

Method: what we add to the raw data

• The source is an open global elevation model at 15 m; its bare-earth terrain was prepared for the whole Kingdom at 90 m, the cell size hydrology tools can carry over this area.
• Depressions were filled only partially, up to twenty metres, not completely: a full fill removes the real closed depressions and makes everything drain to the sea, and those depressions are among the Kingdom's defining features.
• Flow direction was computed with the eight-neighbour method, then flow accumulation per cell, then wadis extracted where 25 km2 or more drains into a cell, each segment carrying its Strahler order.
• Basins were derived from flow direction, each basin being what drains to a single outlet.
• Each basin outlet was classified by the position of its lowest point: within 15 km of the sea it drains to the sea, within the same distance of the national border it crosses the border, otherwise it is a closed depression where the water ends.
• A basin is a natural unit that may cross the border, so its outlet is determined from its full extent (otherwise a false outlet appears at the border), while the published area is what falls inside the Kingdom, with a column for the full area and the share inside.

Product details

Spatial layers

• basins — polygons, 2,359: Basins with area and outlet
• collection_points — points, 2,359: The water collection point of each basin (its lowest point)
• wadis — lines, 40,056: Wadi network with Strahler order

Tables

• D119_basins.csv — 2,359 rows: Basins table
• D119_wadis.csv — 40,056 rows: Wadi segments table
• D119_by_governorate.csv — 101 rows: Basins per governorate

Limitations

• At 90 m cells, small channels inside cities and narrow ravines are not represented; this is a basin-scale product, not a street-scale one.
• Wadis are derived from surface form, not from observed flow: a channel here is a path water would take if it ran, not a permanent river, and most Saudi wadis run only after rain.
• The channel threshold is 25 km2; anything smaller does not appear. It was chosen to suit the Kingdom's aridity, and changing it changes the network density.
• A closed depression here is a hydrological verdict from surface form; some may drain into the ground rather than pond and evaporate.
• The partial fill to twenty metres is a methodological choice: a deeper depression stays closed and a shallower one is filled, so very small basins are sensitive to this limit.
• The elevation model derives from imagery acquired up to 2024, so later earthworks are not represented.
• The area measured from the boundary used here is 1,925,091 km2, less than the commonly cited official figure of about 2,150,000 km2; the difference is between a declared figure and an area measured from a digital boundary.

FAQ

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