Tomebamba (Ecuador)

Basin Overview

The Tomebamba basin is located in the tropical Andes (aprox. 3 degrees South) and ranges from 2500 to 4400 m a.s.l. At its outlet lies the city of Cuenca, the 3rd largest city of Ecuador, both in size and economic importance.  The Tomebamba basin is arguably the main water source for Cuenca’s drinking water system.  From top to bottom the main basin ecosystems are the páramo (grasslands with few partches of native forests), high Andean forests, and close to the city the natural ecosystem has been transformed into an agro-ecosystem with croplands and aquaculture activities. There are no human-made dams in the basin.

The Cajas National Park covers part of the upper Tomebamba, mainly in the páramo ecosystem where a lake system is present. Indeed, the Cajas has more than a thousand water bodies.  Here, rainfall is delivered year-round, with no marked seasonality. Precipitation happens as rainfall and drizzle, and despite the high elevations there is no snow deposition. This contrasts with the rainfall regime at the outlet where a clear bimodal regime exists, with rainfall present mainly in April-May and October, and with dry seasons in July-September and December-January. Historically, December to February is the period hit with the most severe droughts.

Facts and Figures

Country:  Ecuador
State/Region: Azuay
Major Population Centers (people in 2017): Cuenca (500,000)

River Length: 45 km
Watershed Area: 300 km2
Köppen Climate Classification: Subtropical highland climate with uniform rainfall

Source: —
Mean annual precipitation: 1200 mm (3900 m a.s.l.)

Mouth: —
Mean annual precipitation: 850 mm (2600 m a.s.l.)
Mean annual discharge at mouth: 6.5 m3/s

People and Land Use

The only major population is the city of Cuenca. In the lower part of the basin there is a rapid urbanization process. Particularly houses, sport-fishing sites, and restaurants are being built next to the Cuenca-Guayaquil road (that runs parallel to the main river). Sport fishing (and aquaculture in general) is a growing economic activity that is changing the natural landscape next to the river and it is a cause of concern for the drinking water utility, particularly from a water quality perspective.

In the past (70s – 90s), parts of the basin were part of national reforestation plans. Then, native grasslands were transformed to exotic pine plantations. However, given the low growing rates of the trees, this is no longer seen as an attractive economic activity.

Finally, in some parts of the basin natural grasslands and forests and being converted to grasslands for cattle grazing. And intensive grazing, with no management, is producing fast soil degradation and erosion; all of this happening upstream of the drinking water intake.

Major Issues

Water quality will be reduced due to alterations in the basin such as point pollution from households, sport-fishing sites, and restaurants; and non-point pollution from intensive grazing activities.  There is also another concern from non-conventional contaminants such as pharmaceuticals coming from cattle and households.

Water use conflicts will arise from a reduced discharge during droughts, which are becoming from frequent and more intense as well. This will be exacerbated if temperatures continue growing up; thus, the likelihood of hydrological droughts will increase as well. So, the natural regulation capacity of the basin might no longer sustain the needs of the users downstream. And if water demand is not addressed (drinking water demand is around 200 l/hab/day), water use conflicts might be the main issue in the near future.