Abastract Understanding fluvial channels in rock record is difficult and modern river study gives a better understanding of channel facies. Interpretation of remote sensing imagery of the meandering Wahau River shows that the river pattern is changing through time, and it is influenced by seasonal changes. Typical of humid-tropical environment, plant remains are abundant in the river system and seasonal change controls the flow pattern. Field study confirms that grain size of point-bar sediments decreases downstream. Introduction Identification of channel patterns, whether braided or meandering, in ancient fluvial system is very difficult. Identification is very difficult. A survey of available literature on fluvial deposits indicates that it can be even difficult to distinguish among ancient river pattern, as most of the so-called distinguishing features in fact overlap each other (e.g. Jackson, 1978, Collinson, 1978). Modern river study is considered as a good approach to understand ancient fluvial system and this study shows how seasonal change controls the river pattern. Wahau River is located in the north of Muara Wahau, East Kalimantan (Fig. 1). The river is a tributary of the Mahakam River, about 250 km upriver from the Mahakam Delta. The climate is humid-tropical, with precipitation ranged from 2500 to 3000 mm/year, and average temperature between 25oC and 35oC. Water discharge of the Wahau River fluctuates from 18 m3/second during the dry season and 877 m3/second or higher during floods. The river water level also fluctuates enormously by 2-5 meters (Schuettrumpf, 1986). The flood plain of the Wahau River ranges from 200 to 3100 m, controlled by fault in the west and east. The study area covers Miocene to Eocene clastic terrain of deltaic system. The provenance of the present day sediments is the Kuching High metamorphic complex. Remote Sensing Interpretation River channel pattern observation were made from aerial photographs and satellite images to describe the seasonal differences in the hydrology of the river. This was followed-up by field examination of features identified on aerial photographs and satellite images. The synthetic aperture radar (SAR) image and aerial photographs of this area show that the river valley is bounded by faults on the west and east (Fig. 2). The fluvial channel system consists of active and inactive channels, point bars, and stable (commonly densely vegetated) lands. Lineation of the meandering pattern is perhaps fault-controlled. The lower part of the meandering belt cuts the soft shale and siltstone facies. The SAR image and aerial photographs show clearly defined scroll bars, swales and oxbow lakes (Fig. 3). Width of point bars ranges from 5 to 50 m and length of 50 to 500 m. During the rainy season when the river is at flood stage, water flows through chutes, incised in the point bars, or is guided by scroll bars, swales, and ox-bow lakes. Directional features of abandoned channels, scroll bars, and swale topography for the entire meander belt were mapped and statistically analyzed. These data were then subjected to a vector analysis, using 250 m x 250 m grid, to determine the vector mean azimuth (Fig. 4). The rose diagram of directional features determine the general trend of the meandering belt valleys, which is N 20oE.   Field Observation Field examination of two point bars examined only the surface of the bars. Meandering rivers are characterized by point bars, which are deposits made on the convex banks and related to flow patterns in curved channels (Fig. 5). Two point bars have been examined in this area. Four facies with different composition and grain size were identified base on examination of the surface of two point bars. All bars examined generally contained all four facies with similar arrangement as shown in Fig. 6. Pebble Facies Pebble facies is dominated by 2-10 cm in pebbles and cobbles with some sand, and generally lacking in plant fragments. The pebbles are subrounded to well rounded, dominated by quartz and hard metasedimentary rocks. These materials were transported from northwestern basement terrain, upstream of the Wahau River. Pebble facies occurs at the upstream of point bars. Dominant directions of point bar growth and migration are clear in this facies, showed by the pebbles lineation (Fig. 7). Scroll bars occur at the lee side of pebble facies. This part is a transition facies from pebble facies to sand facies. Ripple surface is very distinct and captured as scroll bars in the remote sensing images. Medium Sand Facies Pebbles become smaller and fewer downstream on the point bar and sand become more abundant. The sand is medium to fine in size and rounded to subangular. It is mainly quartz and rock fragments with some plant remains mainly wood debris and twigs (Fig. 8). Fine Sand Facies. Fine sand facies consists of fine to very fine-grained sand, moderately to poorly sorted, some is rippled (Fig. 9). Plant fragments are relatively large and locally abundant. Terraces are common in this facies recording post-flood decline in river stage. Plant Remains Facies Deposits composed mostly of leaves and sticks occur at the downstream ends of point bars. The size of plant debris are range from 0.3 mm to 10 cm. River terraces are also found in this part because it is sensitive to the erosion processes (Fig. 10). The relationship between channel pattern and the seasons When precipitation rate is relatively light, river stage is low, and the river flows totally within its channel, and the upper surfaces of point bars are emergent. During heavy rainfall river stage rizes 3-5 meters above normal stage, and point bars and floodplain are totally submerged (Fig. 11). Flow pattern during flood is relatively straight and constrained by the valley walls.  Conclusions Flow patterns at flood stage differ from those of normal stage. During flood stage the flow pattern is straighter compare to the normal stage. Point bars are gravelly upstream, sandy in the middle, and plant debris dominated at the downstream end. Acknowledgment The author would like to thank Michael McLane (PT. Geoservices) for his constructive comment on the earlier version of this paper. References Collinson, J. D., 1978, Vertical sequence and sand body shape in alluvial sequence, in Miall, a. d., ed., Fluvial Sedimentology: Canadian Society of Petroleum Geology, Memori 5. Jackson, R. G., 1978, Preliminary evaluation of lithofacies modesl for meandering alluvial sreams, in in Miall, a. d., ed., Fluvial Sedimentology: Canadian Society of Petroleum Geology, Memori 5. Schuettrumpf, R., 1986, Hydrological monography of the Mahakam River, Technical Cooperation for Area Development Kutai District, East Kalimantan.