Inflow to Lake Titicaca

Abstract

Lake Titicaca forms part of the great system of internal drainage of the Altiplano of Peru and Bolivia between the Cordillera Oriental and the Cordillera Occidental. The lake has an area of about 8300 sq km (3300 sq mi) and it is about 3800 meters (12,500 ft) above sea level. The adjacent ranges are about 2000 meters (6500 ft) higher. Lake Titicaca normally fluctuates about 60 cm (2 ft) each year and there have been cyclic fluctuations aggregating 4.6 meters (15 ft). Such fluctuations, of which there is a record since 1914, are indicative of variations in inflow but do not reflect the true magnitude of such variations because the rate of outflow is a function of the lake level. There are no records of inflow to Lake Titicaca and few of the outflow from it. Hence, estimates of inflow and outflow had to be based on solutions of the equation of hydrologic balance, including allowance for precipitation on and evaporation from the lake surface. Trial solutions of these equations were made by months until a reasonably consistent set of values was determined. It was concluded from the study that the minimum annual inflow to Lake Titicaca was 37 per cent of the average inflow and that not more than two-thirds of the average runoff of streams on the Altiplano can be counted upon during any decade, even though sufficient storage is provided to carry over that long a period.