East Kalimantan Programme; MAHAKAM

WP5: Discharge regimes, morphometry and tides in the Mahakam delta channel network

Research group
Project leaders:
Dr. A.J.F. Hoitink
Dr. Gadis Sri Haryani

Researcher:
Mr. M. Sassi, MSc

Other participants:
Prof. Dr. Peter A. Troch
Dr. Dirk H. Hoekman
Mr. Paul J.J.F. Torfs, MSc
Dr. Safwan Hadi
Dr. P. Molnár
Mr. M. Schroevers, MSc

3. Summary of the project
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 L-band 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.

4. Detailed description of the project
a. Scientific Background
Hydraulic geometry of a river network
The hydraulic geometry (HG) of a river network can be defined as the relation between discharge and channel morphometric properties such as water surface width, mean depth, cross-sectional area and surface slope. The HG of alluvial rivers has been studied for decades (Leopold and Maddock, 1953), focussing on relationships for different discharges at an individual cross section, or for different downstream locations related through some characteristic discharge of constant frequency of exceedance. The former relations are termed at-site HG, of which the stage-discharge relations have gained widest application (cf. Kuczera, 1999). The latter relations are referred to as downstream HG (cf. Molnár and Ramínez, 2002), and regard for instance the spatial relations between water surface width and bankfull discharge or mean annual discharge. Research into HG relations in river networks has developed into the recent trend to try and find general hydraulic geometry relations on the catchment-scale (Dodov and Foufoula-Georgiou, 2004), and at a subsequent stage to explain the general hydraulic geometry on the basis of physical properties such as channel planform characteristics (e.g. sinuosity, meander wavelength, vegetation characteristics) and channel cross-sectional shape (Dodov and Foufoula-Georgiou, 2004).

Tidal rivers
Tidal rivers are intrinsically more complex than alluvial rivers, as the tidal propagation is influenced by the river discharge and vice versa (e.g. Horrevoets et al., 2004). Whereas stage-discharge relations in alluvial rivers are often useful despite the occurring hysteresis loops as a result of backwater effects, the bidirectional tidal flow superimposed on the river discharge in a tidal river impedes any direct relation between water level and discharge. Since the interaction between river discharge and the tidal motion is nonlinear, complete separation of tidal and river discharges or water levels is infeasible. Variation of water level or mean velocity at tidal frequencies is primarily caused by the tidal motion, but the associated variation of turbulence level and surface slope alternately enhances and counteracts river discharges, leading to river discharge variation at tidal frequencies. In turn, low-frequency variation of water levels and tidal-mean velocity is primarily caused by the river discharge, but may contain a considerable tidal component. In particular, the tidal-mean momentum flux directed upstream is balanced by an upstream mean water level increase, which features a spring-neap cycle as the tidal mean momentum flux covaries with the tidal range. Accordingly, an alluvial discharge wave may be admitted to a delta region preferentially during neap tide.
Contemporary methods for forecasting of water levels in tidal rivers employ neural networks that are trained with time-series of discharge, tidal-mean water level and tidal range (Supharatid, 2003). However, the underlying physics are locked up in a set of optimal weights and threshold values, and are generally not revealed to the user. Alternatively, hydrodynamical models can be employed to analyse the physics governing tidal propagation and discharge distributions, provided that a digital terrain model, boundary conditions and comprehensive dataset on hydraulic roughness are available. Only recently, these models have reached a level of development in which they can simulate inundation events (Stelling, 2002; Hesselink et al., 2003). Information about stage-dependent hydraulic roughness, prerequisite for a hydrodynamic model, can be derived from the at-site HG relation between surface level slope, hydraulic radius and cross-section averaged velocity.

b. Specific Objective(s)
The objective of the present proposal is to establish at-site and downstream HG relations between discharge, tidal and morphometric variables in the freshwater part of the Mahakam delta channel network, and to explain the physical mechanisms behind these relations using hydrodynamic models.For that purpose, new functional relations between hydraulic and morphometric channel variables have to be formulated to apply HG concepts to the case of a river network with tides, which has never been done before. Variables pertaining specifically to tidal rivers include tidal velocity amplitude, tidal average stream depth and tidal range. Downstream HG relations will give empirical information about the river discharge distribution at bifurcations as a function of the tide. Using additional turbidity measurements, this will elucidate how alluvial suspended sediment is being distributed over the delta, which is important to studies in the cluster focussing on mangroves and on the geological evolution of the delta. Knowledge about the HG of the Mahakam tidal river network will provide navigation characteristics of channel sections and insights into the risk of flooding of the delta. From an instrumentation point of view, the proposed analysis will yield the information to monitor discharges using low-cost measurements such as level gauging or remote sensing.
Establishing downstream HG relations requires the definition of consistent recurrence interval events, such as the mean annual discharge. This is related to the finite propagation speed of compound discharge waves that develop under varying rainfall conditions within a river network, causing spatial differences in relative river stage. The mean annual discharge, or any other recurrence interval event, therefore does not occur everywhere in the river network at the same time. Zooming in on a tidal river network such as the Mahakam delta, phase differences in relative river stage can be neglected due to the limited extent of the delta, when compared to the length of a discharge wave. This permits to consider the river discharge at the upstream border of the delta as being normative for the entire delta. Downstream HG relations within the delta will be determined primarily by the interaction between tides and discharge distribution at bifurcations.

Mahakam delta tidal river network
The Mahakam delta has prograded about 60 km over the past 5000 years, resulting in a quasi-symmetric network of tidal and distributary channels. The subaerial delta nowadays covers some 1800 km², consisting of mangrove areas near the shore, Nypa swamps in the central areas, and lowland forest near the apex, corresponding to the fist bifurcation. At the apex, the Mahakam River drains about 75.000 km². From available rainfall data and the size of the drainage basin, the annual mean discharge was estimated by Allen and Chambers (1998) to be in the order of 3000 m³ sec^-1. Floods of up to 5000 m³ sec^-1 may occur in the upper and middle reaches of the catchment, which is separated from the river mouth of the drainage basin by a subsiding area characterized by a low relief alluvial plain and several large lakes, located some 150 km upstream of the delta plain (Roberts and Sydow, 2003). The lakes create a buffer capacity causing the dampening of the flood surges (Allen and Chambers, 1998) and effectively level off Mahakam river floods, resulting in a relatively constant discharge in the lower reaches of the Mahakam river, and in the delta. The absence of peaks in river discharge has resulted in a delta plain that neither features natural levees nor crevasse splays, and avulsions of distributary channels have never taken place. As the delta prograded, bifurcations of the fluvial distributaries occurred about every 10 km. The channels in the Mahakam have variable depths generally ranging in between 3 to 12 m.
There are three reasons that render the Mahakam delta suitable to study HG relations in a tidal network. First, morphodynamic changes in the distributaries are small. Morphology changes influence the at-site as well as downstream HG relations and morphological activity therefore limits the time span over which HG relations are valid. The distributary channels in the Mahakam delta are straight and contain a meandering thalweg. Analysis of aerial photographs dating back some 50 years has confirmed that channel locations are virtually fixed (Allen et al. 1976). Secondly, the absence of floodplains and the geometrical structure of the Mahakam delta justifies the view of the delta as a channel network. Understanding of detailed flow characteristics, e.g. at the location of a bifurcation, requires a two-dimensional approach that accounts for three-dimensional effects (cf. Blanckaert and De Vriend, 2003).

Figure 1 Mahakam delta channel network

A final aspect that facilitates HG analysis in the Mahakam tidal channel network is that baroclinic influences in the distributary channels are limited, which was established during the pilot phase of the project. During the dry season, salinity intrusion typical of estuaries was established to be confined to the first 20 km upstream of the river mouth of the southernmost distributary. The distributary channel subjected to study is the deepest channel of the Mahakam delta, which is maintained at depth to keep the city of Samarinda accessible. The other distributaries are shallower, and therefore are expected to experience a weaker salinity influence. During the wet season, high discharges further push back the saline wedges. Our proposed analysis will be focussed on the distributary reaches free of substantial density differences, which also cause water slope differences and effect HG relations.

c. Workplan
Field campaigns are planned in the wet season of 2006/2007 and in the dry season of 2007, consisting of:

detailed bathymetry mapping on the basis of echo soundings
surface elevation measurements with arrays of self-contained pressure sensors
discharge / turbidity measurements with an Acoustic Doppler Current Profiler (ADCP)
turbidity monitoring with a self-cleaning Optical Backscatter (OBS) sensor.
sediment sampling and characterization of riparian vegetation

Discharges will be measured at the center of rectilinear transects that do not branch off over a length of about 10 km. The ADCP measurements will be taken using a speedboat with limited draft. Site-specific measurement protocols will be developed to ascertain the accuracy of the acoustic discharge measurements (cf. Muste et al., 2004a; 2004b). Pressure sensors will be installed at the beginning and at the end of the specific transect under investigation, to establish the local longitudinal surface level slope. Calculations have shown that the tides in the Mahakam delta channels generate a surface level difference in the order of 40 cm over 10 km at springtide. At the center of a transect under investigation, where the ADCP surveys take place, the OBS sensor will be installed, which will be calibrated in situ. The OBS data combined with ADCP backscatter can be used to establish the cross-channel variation in suspended sediment concentration (Hoitink and Hoekstra, 2005). The investigated transects will be characterized in terms of bottom sediment composition and vegetation at the riverbanks.
Remote sensing images will be employed to obtain a delineation of the Mahakam tidal channel network at stages of the tide coinciding with the passovers of the ALOS satellite, which is planned to be launched in December 2005 and covers peninsular SE Asia (see also point 8 about integration). The PALSAR L-band radar aboard the ALOS is delivers a series of 8 observations (45 days interval) during the first year at 100 m resolution, and additional coverages at 50 m resolution during the whole mission period. Special products with 10 m resolution will be requested, which are expected to yield surface width information. In addition to channel network delineation, the ALOS data will be used to build images of centimeter-scale spatial variation in surface level at the time of the passovers, using multipass interferometry (cf. Alsdorf et al., 2000). It will be investigated if synoptic views of the tidal wave in the delta network can be constructed.
The hydrodynamic modeling part of the project will consist of the setup, calibration and analysis of

a one-dimensional network model to capture the interactions between tides and river discharges at the scale of the delta and
a quasi three-dimensional (Q3D) model of the bifurcation area at the delta apex, to understand the details of the discharge distribution at the main freshwater divide.

Existing models developed at WL|Delft Hydraulics will be used together with WP10, viz. the SOBEK network model and DELFT 3D. A central element in the development of both the network model and the Q3D model will be the stage dependent hydraulic roughness, related to bottom sediment, bed forms and vegetation at the riverbanks. Over the past decade, a major effort has been undertaken in The Netherlands to improve model performance during river surges. The resulting state-of-the-art model components will be validated in a tropical context.

d. Scientific Relevance
See point 4a.

5. Participation in a graduate School ('onderzoeksschool')
The PhD candidate will participate in the SENSE Research School for Socio-Economic and Natural Sciences of the Environment.

6. Scientific performance of members of the research group(s)

Hoitink, A.J.F., Hoekstra, P., and Van Maren, D.S.(in press). Comment on "On the role of diurnal tides in contributing to asymmetries in tidal probability distribution functions in areas of predominantly semi-diurnal tide" by P.L. Woodworth, D.L. Blackman, D.T. Pugh and J.M. Vassie. To appear in Estuarine, Coastal and Shelf Science.
Storms, J.E.A., R.M. Hoogendoorn, M.A.C. Dam, A.J.F. Hoitink and S.B. Kroonenberg (2005) Late-Holocene evolution of the Mahakam delta, East Kalimantan, Indonesia. Sedimentary Geology 180(3-4) 149-166
Hoitink, A.J.F., & Hoekstra, P. (2005). Observations of suspended sediment from ADCP and OBS measurements in a mud-dominated environment. Coastal Engineering, 52(2), 103-118.
Maren, D.S. van, Hoekstra, P., & Hoitink, A.J.F. (2004). Tidal flow asymmetry in the diurnal regime: bed load transport and morphologic changes around the Red River Delta. Ocean dynamics, 54(3), 424-434.
Hoitink, A.J.F. (2004). Tidally-induced clouds of suspended sediment connected to shallow-water coral reefs. Marine Geology, 208(1), 13-31.
Hoitink, A.J.F., Hoekstra, P., & Maren, D.S. van (2003). Flow asymmetry associated with astronomical tides: Implications for the residual transport of sediment. Journal of Geophysical Research, 108(C10), 3315-3315.
Hoitink, A.J.F., & Hoekstra, P. (2003). Hydrodynamic control of the supply of reworked terrigenous sediment to coral reefs in the Bay of Banten (NW Java, Indonesia). Estuarine, Coastal & Shelf Science, 58(4), 743-755.
Gadis Sri Haryani and PE Hehanusa . 1997. Preliminary Ecotone Studies of two Lakes in Sulawesi Island its relevance to Lake Management Planning. Proceedings Workshop on ecosystem Approach to lake and reservoir Management, International Hydrology Programme, Bali 22-25 July. Page 87-194
P.E. Hehanussa and Gadis Sri Haryani. 2000. The Changing Perspective of water resources management policy in Indonesia, Fresh Perspectives, New Zealand Hydrological Society, Meteorological Society of New Zealand, New Zealand Limnological Society.
P.E. Hehanussa and Gadis Sri Haryani. 2001. Neglected water resources potentials of Indonesian Lakes, An Ecohydrology Approach. Proceedings Asia-Pacific Workshop on Ecohydrology, Cibinong- Bogor, Indonesia. P. 111-120.
Gadis Sri Haryani.2001. The Role of Poso Estuary Ecosystem in Elver Eels (Anguilla spp) Anadromous Migration. Proceedings Asia-Pacific Workshop on Ecohydrology, Cibinong-Bogor, Indonesia. P. 119-224
P.E. Hehanussa and Gadis Sri Haryani. 2001. The Evolution and Indonesian Water Law: Problem, Obstacles, and Expectations. Proceedings of Symposium on Innovative Approaches for Hydrology and water Resources Management in the Monsoon Asia. The University of Tokyo, Japan.P.93-97.
Gadis Sri Haryani. Changes in ecohydrology of Lake Poso catchment and its effects to the life cycle of eel Anguilla marmorata. Advanced Study Course in Ecohydrology di Polandia, Hungaria, Austria, Croatia, Italy, 1999
Gadis Sri Haryani. 2001. The role of estuary Ecosystem of Poso River in elver eels (Anguilla spp.) anadromous migration. Asia-Pacific Workshop on Ecohydrology. Cibinong-West Java March, 2001
Gadis Sri Haryani & P.E. Hehanussa. 2001. River basin, Governance Decentralization, and Ecohydrology for WRM in Indonesia. The international Symposium on "Achievements of the IHP-V in Hydrological Research" , November 2001
Gadis Sri Haryani. The future of limnological research in Indonesia. 2nd Asia-Pacific Workshop on Ecohydrology. Cibinong-West Java March, 2003
Gadis Sri Haryani. Role of the research center for Limnology LIPI in Indonesian Aquatic Studies. Indonesian – Italian Round Table Discussion on Ecohydrology: River Load and Eutrophication, 21-22 June 2004, Jakarta
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Lin, D.S.; Wood, E.F.; Mancini, M; Troch, P.; Jackson, T. (1993). Comparisons of Remotely Sensed and Model Simulated Soil Moisture Over a Heterogeneous Watershed, Remote Sensing of Environment, 48, 159-171.
Altese, E.; Bolognani, O.; Mancini, M.; Troch, P.A. (1996). Retrieving Soil Moisture Over Bare Soil From ERS-1 Synthetic Aperture Radar Data: Sensitivity Analysis Based on a Theoretical Surface Scattering Model and Field Data, Water Resources Research, 32(3), 653-661.
Troch, P.A.; Su, Z.; De Troch, F.P. (1996). Remote Sensing of Surface Soil Moisture Using EMAC/ESAR Data, Earth Observation Quarterly, ESA, (53), 17-21.
Su, Z.; Troch, P.A.; De Troch, F.P. (1997). Remote Sensing of Soil Moisture Using EMAC/ESAR Data, International Journal of Remote Sensing, 18(10), 2105-2124.
Schoups, G.; Troch, P.A.; Verhoest, N. (1998). Soil Moisture Influences on the Radar Backscattering of Sugar Beet Fields, Remote Sensing of the Environment, 65, 184-194.
Verhoest, N.; Troch, P.A.; Paniconi, C.; De Troch, F.P. (1998). Mapping basin scale variable source areas from multitemporal remotely sensed observations of soil moisture behaviour, Water Resources Research, 34(12), 3235-3244.
Mancini, M.; Hoeben, R.; Troch, P.A. (1999). Multifrequency radar observations of bare surface soil moisture content, a laboratory experiment, Water Resources Research, 35(6), 1827-1838.
Hoeben, R.; Troch, P.A. (2000). Assimilation of active microwave observation data for soil moisture profile estimation, Water Resources Research, 36(10), 2805-2819.
Van Loon, E.E.; Troch, P.A. (2002). Tikhonov regularization as a tool for assimilating soil moisture data in distributed hydrological models, Hydrological Processes, 16, 531-556.
Schuurmans, J.M.; Troch, P.A.; Veldhuizen, A.A.; Bastiaanssen, W.; Bierkens, M. (2003). Assimilating remotely sensed latent heat fluxes in a distributed hydrological model, Advances in Water Resources, 26(2), 151-159.
Troch, P.A.; Paniconi, C.; McLaughlin, D. (2003). Preface: Catchment-scale hydrological modeling and data assimilation, Advances in Water Resources, 26(2), 131-135.
Wojcik, R., P. Torfs and P. Warmerdam (2003) Application of Parzen Densities to probabilistic Rainfall-Runoff Modelling. J Hydrol Hydromech, 51, 175-186
Peters, E., P. Torfs, H. van Lanen en G Bier (2003) Propagation of drought through groundwater - a new approach using linear reservoir theory. Hydrol Processes, 17, 3023-3040
De Lima, J., P. Torfs en V. Singh (2002) A mathematical model vor evaluating the effect of wind on downward-spraying rainfall simulators. Catena 46, 221-241
Torfs, P., R. Wojcik Local Probabilistic Neural Networks in Hydrology, Phys Chem Earth (B), vol 26, no 1 pp 9-114
Torfs, P., E. van Loon, R Wojcik en P Troch (2002) Data assimilation by non-parametric local density estimation. Computational Methods in Water Resources, ed S Hassanizadeh, pp 1355-1362
Wojcik, R., P. Torfs and P. Warmerdam (2003) Application of Parzen Densities to probabilistic Rainfall-Runoff Modelling. J Hydrol Hydromech, 51, 175-186
Quińones, M.J., and D.H. Hoekman, 2004, Exploration of factors limiting biomass estimation by polarimetric radar in tropical forests, IEEE Transactions on Geoscience and Remote Sensing, Vol.42, No.1, January 2004, pp.86-104.
Hoekman, D.H., and M.A.M. Vissers, 2003, A new polarimetric classification approach evaluated for agricultural crops, IEEE Transactions on Geoscience and Remote Sensing, Vol.41, No.12, December 2003, pp.2881-2889.
Varekamp, C., and D.H. Hoekman, 2002, High-resolution InSAR image simulation for forest canopies, 2002, IEEE Transactions on Geoscience and Remote Sensing, Vol.40, No.7, pp.1648-1655, July Issue.
Hoekman, D.H. and C. Varekamp, 2001, Observation of tropical rain forest trees by airborne high resolution interferometric radar, IEEE Transactions on Geoscience and Remote Sensing, Vol.39, No.3, pp.584-594.
Varekamp, C and D.H. Hoekman, 2001, Segmentation of high-resolution InSAR data of tropical forest using Fourier parameterised deformable models, International Journal of Remote Sensing, Vol.22, No.12, pp.2339-2350.
Woodhouse, I.H. and D.H. Hoekman, 2000, Determining land surface parameters from the ERS-windscatterometer, IEEE Transactions on Geoscience and Remote Sensing, Vol.38, pp.126-140.
Hoekman, D.H. and M.J. Quińones, 2000, Land cover type and biomass classification using AirSAR data for evaluation of monitoring scenarios in the Colombian Amazon, IEEE Transactions on Geoscience and Remote Sensing, Vol.38, pp.685-696.

7. Literature references

Allen, G. P. and Chambers, J. L. C. (1998). Sedimentation in the Modern and Miocene Mahakam delta. Jakarta, Indonesian Petroleum Association. 236
Allen, G. P., Laurier, D. and Thouvenin, J. (1976). Sediment distribution patterns in the modern Mahakam delta. Proceedings Indonesian Petroleum Association: 159-178.
Blanckaert, K., and H. J. de Vriend (2003), Nonlinear modeling of mean flow redistribution in curved open channels, Water Resour. Res., 39(12), 1375, doi:10.1029/2003WR002068.
Dodov, B. and E. Foufoula-Georgiou (2004) Generalized hydraulic geometry: Derivation based on a multiscaling formalism. Water Resour. Res. 40(6) doi: 10.1029/2003WR002082
Dodov, B. and E. Foufoula-Georgiou (2004) Generalized hydraulic geometry: Insights based on fluvial instability analysis and a physical model. Water Resour. Res. 40(12), doi: 10.1029/2004WR003196, 2004
Hesselink, A.W., G.S. Stelling, J.C.J. Kwadijk and H. Middelkoop (2003) Inundation of a Dutch river polder, sensitivity analysis of a physically based inundation model using historic data. Water Resour. Res. 39(9), 1234, doi:10.1029/2002WR001334
Hoitink, A.J.F., & Hoekstra, P. (2005). Observations of suspended sediment from ADCP and OBS measurements in a mud-dominated environment. Coastal Engineering, 52(2), 103-118.
Horrevoets, A.C., H.H.G. Savenije, J.N. Schuurman, S. Graas (2004) The influence of river discharge on tidal damping in alluvial estuaries. J. Hydr. 294, pp. 213-228
Kuczera, G. (1999) Comprehensive at-site flood frequency analysis using Monte Carlo Bayesian inference. Water Resour. Res. 35(5) pp 1551-1557
Leopold, L.B. and T. Maddock (1953) The hydraulic geometry of stream channels and some physiographic implications, U. S. Geol. Surv. Prof. Paper, 252, 57 pp.
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Muste, M., K. Yu, T. Pratt and D. Abraham (2004b) Practical aspects of ADCP data use for quantification of mean river flow characteristics; Part II: fixed-vessel measurements. Flow Measurement and Instrumentation 15(1) pp 17-28
Roberts, H. H. and Sydow, J. (1996). The offshore Mahakam delta: stratigraphic response of late Pleistocene-to-modern sea level cycle. Proceedings Indonesian Petroleum Association 25: 147-161.
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