Tidal impact on the division of river discharge over distributary channels in the Mahakam Delta
- 782 Downloads
Bifurcations in tidally influenced deltas distribute river discharge over downstream channels, asserting a strong control over terrestrial runoff to the coastal ocean. Whereas the mechanics of river bifurcations is well-understood, junctions in tidal channels have received comparatively little attention in the literature. This paper aims to quantify the tidal impact on subtidal discharge distribution at the bifurcations in the Mahakam Delta, East Kalimantan, Indonesia. The Mahakam Delta is a regular fan-shaped delta, composed of a quasi-symmetric network of rectilinear distributaries and sinuous tidal channels. A depth-averaged version of the unstructured-mesh, finite-element model second-generation Louvain-la-Neuve Ice-ocean Model has been used to simulate the hydrodynamics driven by river discharge and tides in the delta channel network. The model was forced with tides at open sea boundaries and with measured and modeled river discharge at upstream locations. Calibration was performed with water level time series and flow measurements, both spanning a simulation period. Validation was performed by comparing the model results with discharge measurements at the two principal bifurcations in the delta. Results indicate that within 10 to 15 km from the delta apex, the tides alter the river discharge division by about 10% in all bifurcations. The tidal impact increases seaward, with a maximum value of the order of 30%. In general, the effect of tides is to hamper the discharge division that would occur in the case without tides.
KeywordsSubtidal dynamics Finite elements River-tide interaction Hydrodynamic model Deltas Mahakam River discharge Differential water level setup
This study is part of East Kalimantan Programme, supported by grant number WT76-268 from WOTRO Science for Global Development, a subdivision of the Netherlands Organisation for Scientific Research (NWO). E. Deleersnijder is a Research Associate with the Belgian Fund For Scientific Research (F.R.S. - FNRS). His contribution to the present study, as well as that of B. de Brye, was achieved in the Framework of ARC 10/15 - 028 (Communauté Française de Belgique). Fajar Setiawan and Unggul Handoko (Indonesian Institute of Sciences) are acknowledged for their contribution to the field campaigns. We thank Pieter Hazenberg and Johan Romelingh (Wageningen University) for the technical support. The first author thanks Frans Buschman for the constructive criticism on the draft of this manuscript. The Associate Editor and an anonymous reviewer have helped improve the draft of this paper with constructive criticism.
- Allen GP, Chambers JLC (1998) Sedimentation in the modern and Miocene Mahakam delta. Indonesian Petroleum Association, Jakarta, p 236Google Scholar
- Bertoldi W, Tubino M (2007) River bifurcations: experimental observations on equilibrium configurations. Water Resour Res 43(10). doi: 10.1029/2007WR005907
- de Brye B, Schellen S, Sassi M, Vermeulen B, Kärnä T, Deleersnijder E, Hoitink T (2011) Preliminary results of a finite-element, multi-scale model of the mahakam delta (Indonesia). Ocean Dyn 1–14 (in press). doi: 10.1007/s10236-011-0410-y
- Buschman FA, Hoitink AJF, Van Der Vegt M, Hoekstra P (2009) Subtidal water level variation controlled by river flow and tides. Water Resour Res 45(10). doi: 10.1029/2009WR008167
- Buschman FA, Hoitink AJF, Van Der Vegt M, Hoekstra P (2010) Subtidal flow division at a shallow tidal junction. Water Resour Res 46(12). doi: 10.1029/2010WR009266
- Dinehart R, Burau J (2005a) Averaged indicators of secondary flow in repeated Acoustic Doppler Current Profiler crossings of bends. Water Resour Res 41. doi: 10.1029/2005WR004050
- Lutz G, Hubbell D, Stevens HJ (1975) Discharge and flow distribution, Columbia River estuary. Tech. rep., Geological Survey Professional Paper No., p 433Google Scholar
- Rennie C, Millar R, Church M (2002) Measurement of bed load velocity using an Acoustic Doppler Current Profiler. J Hydraul Eng 128:5:473–483Google Scholar
- Sassi M, Hoitink A, Vermeulen B, Hidayat (2011) Discharge estimation from H-ADCP measurements in a tidal river subject to sidewall effects and a mobile bed. Water Resour Res 47(W06504). doi: 10.1029/2010WR009972
- Simpson M (2001) Discharge measurements using a broad-band Acoustic Doppler Current Profiler. Tech. rep., United States Geological SurveyGoogle Scholar