Three methods for determining the area–depth relationship of Lake Poopó, a large shallow lake in Bolivia
Lake Poopó in Bolivia is a large, extremely shallow lake. The lake surface area is ≈3000 km2 at its spill-over level, although it could dry out at times. The lake water level varies with the regional rains and with the water inflow from the Desaguadero River. This study focuses on using and comparing three different approaches to determine the hypsographic curve for the lake. As the lake is extremely shallow, depth measurements must be conducted from a slowly moving boat using a rod. The accuracy using echo-sounding of the lake is poor. The second approach, which can be applied because the lake water level can vary considerably, and because the lake sometimes is almost dry, is to relate the lake surface area determined from satellite images to elevations determined from benchmarks on an island in the lake. The third method is an indirect one, in which the change in lake water volume over the period between two satellite images is determined from water balance computations and subsequently related to changes in the water surface area, as determined from the satellite images. Determination of the shoreline for different water levels in the lake is affected by errors related to the tilting of the water surface, and because wind forces the water to move several hundred metres towards the windward shore of the lake during a measurement survey.