Using satellite altimetry data to augment flow estimation techniques on the Mekong River

Satellite altimetry is routinely used to provide levels for oceans or large inland water bodies from space. By utilizing retracking schemes specially designed for inland waters, meaningful river stages can also be recovered when standard techniques fail. Utilizing retracked waveforms from ERS-2 and ENVISAT along the Mekong, comparisons against observed stage measurements show that the altimetric measurements have a root mean square error (RMSE) of 0.44-0.65 m for ENVISAT and 0.46-0.76 m for ERS-2. For many applications, however, stage is insufficient because discharge is the primary requirement. Investigations were therefore undertaken to estimate discharges at a downstream site (Nakhon Phanom (NP)) assuming that in situ data are available at a site 400 km upstream (Vientiane). Two hypothetical, but realistic scenarios were considered. Firstly, that NP was the site of a de-commissioned gauge and secondly, that the site has never been gauged. Using both scenarios, predictions were made for the daily discharge using methods with and without altimetric stage data. In the first scenario using a linear regression approach the altimetry data improved the Nash-Sutcliffe r(2) value from 0.884 to 0.935. The second scenario used known river cross-sections while lateral inflows were inferred from a hydrological model: this scenario gave an increase in the r(2) value from 0.823 to 0.893. The use of altimetric stage data is shown to improve estimated discharges and further applications are discussed. Copyright (C) 2010 John Wiley & Sons, Ltd.