Discharge regimes, morphometry and tides in the Mahakam delta channel network
10 / 2007 - 12 / 2012
Relations between river discharge and channel characteristics such as mean depth, surface width and surface slope are known as the hydraulic geometry (HG). The so-called at-site HG concerns channel properties at an individual location, whereas the downstream HG relates channel properties from different downstream locations through some characteristic discharge of constant frequency of exceedance (e.g. bankfull discharge). Tidal rivers are intrinsically more complex than alluvial rivers, since the river discharge interacts nonlinearly with the tide. The present proposal is to formulate new HG relations that can be applied to the freshwater part of a tidal river network. In specific, the objective is to establish and explain at-site and downstream HG relations between discharge, tidal and morphometric variables in the Mahakam delta distributary system, which can be regarded as a lowland tidal river network. The proposed methods include field measurements, remote sensing for observation of water surface width and height, and hydrodynamic modelling. The field campaign encompasses bathymetric surveys, installation of water level gauges, ADCP discharge measurements, sediment sampling and characterisation of riparian vegetation. Discharges obtained from ADCP surveying are expected to be function of mean depth and longitudinal surface slope from level gauging. A hydrodynamic model will be used after calibration to establish downstream HG relations, and to investigate the physical mechanisms that result in the HG relations found. The relations between sediment and freshwater discharges, tides and morphometry in the Mahakam delta will allow to evaluate and anticipate effects of sealevel rise, climate change and ongoing human interference. Issues relevation for society include the risk of flooding and navigability of channel sections. Appropriate scenarios will be setup in collaboration with the other research groups in the cluster. Understanding the hydraulics of the delta is important to each of the other research groups within the cluster, as the alluvial flows in the tributaries under the influence of tides are the principal agents of sediment dispersal. The remote sensing component in this proposal is based on PALSAR Lband radar aboard the ALOS satellite, which covers peninsular Southeast Asia. The use of radar water surface measurements in hydraulic research broadens the application domain of ALOS satellite.