Natural Vilcabamba: Natural Foundations of Vilcabamba's Environment: Rivers and Hydrology

RIVERS AND HYDROLOGY

Vilcabamba’s rivers are by turns life-giving and destructive, and a source of both pleasure and frustration for local residents and tourists alike. The rivers are the source for piped water, and support more than a dozen irrigation projects covering hundreds of hectares of land. Many residents bathe and do laundry in the rivers, picnic on their shores, and swim and float on inner-tubes in the deeper sections. But the rivers are also associated with erratic, sudden and sometimes dangerous torrents, flooding and course changes. The extremes in character are linked to both the nature of the rivers, and to climate.

The Rivers of Vilcabamba (see map)

From the southeastern end of the valley flow the Rio Yambala (which supplies piped water to Vilcabamba and the surrounding barrios) and the Rio Capamaco. These two rivers join just southeast of town, to form the north-flowing Rio Chamba. The Rio Colanuma and Rio Banderilla flow from the northeastern end of the valley, and join to form the Rio Uchima.

The Uchima and Chamba rivers join at the bridge on the road to Loja, at the north end of town, to form the Rio Vilcabamba. This feeds into the Catamayo-Chira river system, draining to Peru and the Pacific Ocean.

Sourcewaters

Near the continental divide in Podocarpus Park, at around 3200 m (10,500 ft), are a series of small lakes. (The continental divide, which runs north/south in the Park, is the height of land down which one side the rivers run to the Pacific Ocean, and down the other, to the Amazon River in the Oriente.) These lakes, whose bowl-like basins (cirques) were carved by glaciers, are the headwaters of Vilcabamba’s rivers. As the rivers cascade rapidly down into the valley, they pick up water from many springs and streams.

Torrents, Floods and Course Changes

River surges and flash floods are a fact of life in Vilcabamba. Heavy, concentrated rainfall in the watersheds that feed the valley’s rivers can turn these normally small, contained watercourses into raging torrents that carry large trees and boulders and careen over their banks. One obvious example of the damage, pictured in the photo at right, is the “funhouse” angle of the footbridge over the Rio Chamba, to the northeast of the town. This is one of the more obvious signs remaining from the flash flood that occurred in the Rio Chamba in February 1999. The volume and velocity of the water also forced changes in river-course that continue to play out, in turn affecting the location and stability of shorelines.

Sediment build-up is a major factor influencing the course of Vilcabamba’s rivers. Levels of erosion in the valley are naturally high, but have been increased by human activity. The intensity of water surges may also be greater due to deforestation and burning. But it would be wrong to imply that surges, floods and course changes can be blamed solely on human activity in the valley. Over 60 years ago, when much of the watershed of the Chamba River was still in its natural state, the human population was concentrated along the shores of this river, east of the current town. A shift to the current location of the town was partly inspired by a destructive flood that caused significant loss of livestock and property. (Also, on an ongoing basis, high wet-season water tables made a mess of the earthen floors of homes close to the river.)

RIVER SHAPERS

Slope

During their descent down the steep slopes of mountains, the river channels tend to be relatively straight and deep because of the sheer velocity of the water.
As the rivers descend into the valley, their flow slows and they become more meandering.

The Andes are young mountains, so levels of erosion are naturally high.
When forests are cut and ground cover removed, the soil is exposed; and so it is more easily “loosened” and carried down slopes by the rain. Also, exposed slopes are less stable, so more prone to slide when saturated.
Soils and other materials from gradual erosion and from slides are washed into watercourses.
These sediments settle out in the river channel where the water slows down; that is, in areas of least slope, and on the inside of bends.
Sediment build-up in turn results in a shallower and wider bed, more prone to “meander”. (See photo this page.) “Braiding” (where the river divides into more than one channel) typically occurs where there is a lot of gravel and cobbles in the riverbed.

Natural periods of high rainfall result in high volumes and velocity of water. Deforestation, heavy grazing and burning have also reduced the water-retaining ability of the soils. Faster run-off means more dramatic surges.
Where the watercourse is shallow, water surges cause the river to flood into new areas and to cut new channels.
With higher volume and velocity, the river cuts into its banks at the outside of curves, resulting in shoreline erosion. Strong banks can contain a river and keep it straight. Shoreline deforestation makes riverbanks more susceptible to erosion.

Waters of Longevity?

The quality of Vilcabamba’s water has been identified as one possible reason for the health and reputed longevity of the local population. As the rain that feeds the headwaters of Vilcabamba’s rivers filters through the thick mat of vegetation in the paramo (see The Regional Context in Section 2), it picks up minerals, including manganese, magnesium, selenium and zinc. Among other benefits, the manganese in the water is a chelating agent. It chemically binds with metals, including toxic heavy metals such as lead and mercury, so that they are neutralized and are more easily flushed from the body. This may account for the apparently very low concentration of these toxic metals in Vilcabamba’s older people. A healthy ratio of calcium to magnesium in the valley’s elders has also been attributed to the water, and is associated, among other things, with reduced risk of osteoporosis. The Agua de Hierro water is said to have additional medicinal benefits. (See the paragraph about the iron-rich cliffs above the Agua de Hierro spring, under the Geology and Soils heading in Section 1.)

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