A reconnaissance study was set up and data on precipitation, pan-evaporation, ground water levels and river water levels were collected to study the flow characteristics and storage of the Bika catchment, a small subcatchment of the Kapuas river on West-Kalimantan, Indonesia. This research contributes to the understanding of the hydrological interactions between wetlands, peat areas and rivers.
Hydro(geo)logical flow characteristics of the Bika catchment, a subcatchment of the Kapuas river, Indonesia A reconnaissance study
Supervisors: Roel Dijksma (WUR), Henny van Lanen (WUR), Gusti Anshari (UNTAN)
In the Bika catchment, a small subcatchment of the Kapuas river in Indonesia, the hydro(geo)logical flow characteristics and water balance have been studied. The Kapuas river stretches over 1100 km and is the world's longest river on an island. Very few studies have focussed on the hydrology of peatland forests and even fewer on the peatlands in the Kapuas basin. A field reconnaissance took place to select an accessible, forested, peatland area as a small catchment, representative for the Kapuas basin. This research contributes to the understanding of the hydrological interactions between wetlands, peat areas and rivers. Based on the criteria, the Bika catchment was selected as the most representative subcatchment. From September 16th until December 16th 2013 a field campaign was set up to collect data on precipitation, pan-evaporation, ground water levels and river water levels. Spatial distribution of precipitation was measured by 10 rain gauges and interpolated by IDW. Actual evapotranspiration is calculated from pan-evaporation, whereas ground water levels were monitored by piezometers. The discharge of the river is derived by measuring the streambed profile at several locations, water level and velocity measurements. The Q-h relation showed a hysteresis loop, with both high and low discharges for high water levels, due to the backwater influence of the Kapuas on the Bika. From these data the water balance was calculated, with a precipitation amount of 823 mm, actual evapotranspiration of 239 mm and a total discharge of 776 mm, resulting in a storage change of -192 mm over the period from October 19th until December 14th 2013. The spatial variability in precipitation was high, ranging from 8.8 mm to 109.9 mm for December 9th – 11th, resulting in a possible deviation in the total precipitation amount. Also actual evapotranspiration and total discharge were overestimated due to the spatial variability in the area. Ground water levels, as well as upstream river water levels and visual observations, showed that the area was storing water instead of the negative storage change calculated with the water balance. Storage not only occurred in the soil, but also large areas of forest flooded during high river water levels, with water levels up to 1 m and more in the forest. The areas along the Bika formed large inundation areas to store the water in the Bika catchment.