In order to acquire a better understanding of the hydrological dynamics of the Upper Kapuas Basin in West Kalimantan, a field study at sub-catchment scale was performed. By collecting and analyzing rainfall, evapotranspiration, interception, soil moisture, groundwater levels and discharge data, a good impression of the hydrological behavior of the Bika catchment was obtained.
Hydrological dynamics of a tropical sub-catchment of the Kapuas River, West Kalimantan, Indonesia.
Supervisors: Ryan Teuling (WUR), Gusti Anshari (UNTAN)
In West Kalimantan, Indonesia, only few studies have been conducted on the hydrological properties of the largest river in the world located on an island, namely the Kapuas River. Stretching over more than 1100 km, this river is of key importance for the livelihood conditions for habitants of West Kalimantan. A study at a sub-catchment scale was performed to acquire a better understanding of the hydrological behavior of the Upper Kapuas basin. In the period between October 2013 and December 2013, three field campaigns were held in order to assess the hydrological dynamics of the Bika catchment by collecting: rainfall, evapotranspiration, interception, soil moisture, groundwater levels and discharge data.
The months October until April can be characterized as the wet season and May until September can be characterized as the dry season. It can be concluded that precipitation occurs mainly during convective storms with high intensity. The actual evapotranspiration for the Bika catchments is estimated at 1240 mm/year with an error margin of 200 mm. It was calculated that the average interception percentage for thirteen precipitation events was 24.6 %. As the Bika catchment is still covered for 80 % with secondary forest the buffering influence for the catchment by interception is substantial and interception likely plays a significant role in reducing the fraction of rain that eventually ends up in the river. By analyzing the temporal dynamics of soil moisture it was found that even in the dry season the mean volumetric soil moisture is high, leaving not much room for buffering of precipitation events. An increase over time of the mean volumetric soil moisture was measured with an average of 45.3% in the first field campaign, 53.9% in the second field campaign and 87.5% in the third field campaign. The water level fluctuations were remarkably high in the Bika catchment with an increase in water levels of up to 8 meters. Combining the results of all the measured hydrological factors, the catchment can be categorized as a simple dynamic fast responding system as water level fluctuations reacted almost immediately to the presence or absence of precipitation.
Although the area is a fast responding system, from an event analysis it can be seen that there are still some buffering characteristics that result in a more gradual behavior of the water levels. In terms of hydrological dynamics the secondary forest is not only important for intercepting rainfall and therefore reducing the direct rainfall runoff ratio, but is also very important as open water storage reservoir. If this area would be drained flood risks would probably increase drastically for inhabited areas downstream.