Monitoring and analysis of lowland river discharge

In single-thread channels with a sloping bed and quasi-steady con- ditions, river discharge can often directly be inferred from the water level using a rating curve. Challenges occur when the bed slope becomes negligibly small, or when the discharge becomes highly dynamic such as in the case of tides. This paper discusses recent work on monitoring and analysis of river discharge dynamics under such complicating circumstances. In lowland rivers, backwater has an effect on water levels that extends over a large region for smaller bed slopes. Results from a rainfall-runoff model and discharge measurements in the Mahakam catchment show that when a rating curve is developed in a backwater effected river, it essentially filters the backwater effects out of the discharge series. In coastal lowland plains, marine impacts cannot be ignored. Tidal waves may propagate hundreds of kilometers inland and interact with the river discharge. Acoustic Doppler current profilers are increasingly being employed for discharge monitoring in lowland rivers. A recently developed error model shows that the acoustic range needs to extend beyond the distance from the river bank where the depth mean flow velocity exceeds the cross-section averaged velocity.