Mekong River Modelling
The contributers would like to thank the Mekong Commision for their generous assistance in providing in-situ measurements for this work.
Team: S. J. Birkinshaw, G. M. O’Donnell, P. Moore, C. G. Kilsby, H. J. Fowler, P. A. M. Berry
Research in the use of altimetry in hydrological modelling is a new and exciting area opening up the eventual potential of monitoring ungauged catchments. As a contribution to the ESA Rivers and Lakes project Newcastle University is investigating the potential of altimetric stage heights and in particular the conversion to discharge.

It is noted that:

• Over much of the Earth in situ gauge data of stage and discharge has declined over the past decades.
• In contrast satellite altimetry is adding to the time series of measurements of inland water (stage) heights
• In hydrology discharge is of more interest than stage

The Mekong river has been selected as a test-bed. Gauge data has been supplied by the Mekong River Commission (http://www.mrcmekong.org/). Figure 1 shows the available observed stage and altimetry data. The altimetry data are obtained every 35 days, with the day of pass indicated. A comparison has been made of the ERS-2 and ENVISAT altimetric measurements and observed stage heights at Vientiane. The upper plot of Figure 2 shows this comparison relative to an arbitrary datum while the lower plot gives the differences.

As a preliminary to monitoring ungauged catchments ongoing research aims to first determine to what extent can the discharge downstream of a gauged site (e.g.Vientiane) be predicted from the altimetric stage measurement at the downstream site. In practice, this reflects this scenario that major rivers are still gauged but that the number of gauges has declined over the past decades.