4)	 
Sediment	 loading	 processes	 in	 a	 tectonic	 and	 forested	 catchment	 	  	  	  	  	  	  *Md Motaleb Hossain1, Kazuhisa A. Chikita2, Wataru Iwasaka1 and Takuto Miyamoto1	  	  	  	  	  	  	  1. Graduate School of Science, Hokkaido University 2. Faculty of Science, Hokkaido University	  1. Introduction: Exploring fluvial sedimentary processes
on catchment scale is useful for studies on the forest
management, material cycle and ecosystem of short timescale and topographic evolution of long time scale. The
fluvial transportation of sediment is also related tosedimentation, material cycle and ecosystem in coastal
regions. A considerable portion of suspended sediment
discharging into a coastal lagoon, the Oikamanai Lagoon,
Tokachi, Hokkaido, Japan (Fig. 1) annually is contributedby the forested (ca. 90% area) Oikamani River catchmentwith many tectonic faults. It is important to find out thesediment source in such forested catchments. Here, we have
tried to find out how sediment load occurs by rainfall andsnowmelt runoffs in the tectonic and forested catchment.
2. Methodology: Grain size and mineralogy of catchment
soil and stream sediment, survey techniques, andturbidimeters provide the information that allows us tounderstand fluvial sedimentary processes and the sedimentsource and its availability. Here, a semi-distributed model,ArcSWAT2012, is applied to time series of discharge andsediment load, which were obtained in 2011 to 2013. In2013, we set two gauging stations, site R1 and site R3, toget discharge and suspended sediment concentration timeseries (Fig. 1). In ArcSWAT2012, the total basin area
(62.47 km2) was divided into 3 sub-basins, as subbasins
into hydrological response unit (HRU) based on soil type,land use and slope classes that allow a high level of spatial
detail simulation. In this study we have used the data ofdischarge, Q (m3/s), suspended sediment concentration(SSC; C, mg/L) and sediment load, L (kg/s) of April
2011 to November 2013 on non-frozen period of thesethree years, weather data of 2008 to 2013, and soil data.
3. Results and Discussions: The semi-distributed
SWAT model is applied to model discharge andspatiallydistributed
soil
erosion/sedimentation
processes at daily time step. A reasonable agreement isobtained between the model discharges predictions andmeasured discharge at the basin outlet (Fig. 2). The
simulations of sediment load time series indicate thatmost of the sediment input is coming from sub-basin 2(Fig. 3). Most of the time sediment load at R3 greater thanat R1 (Fig. 4) indicates that the sediment is deposited
between R1 and R3. At present, the interpretation of thequantitative results is not yet satisfactory, because of lackof model parameterization at a local scale in the SWAT
model. This results from the fact that the information onhydrological structures of soil and bedrock is not sufficient.
Thus, a comparison with the other modelling is essential tounderstand the sediment loading processes on catchment
scale.

Fig. 1.	  Observation sites in the Oikamanai river basin.	  

Fig. 2. Discharge Simulation.	  

Fig. 3. Sediment load at Subbasins 1, 2 & 3.	  	  Fig. 4. Sediment load at sites R1 and R3.