Dong Cao catchment
The peri-urban Dong Cao catchment (49.7 ha) is located within the hills of Tien Xuan in the Thach That district of Hanoi, Hoa Binh province, in Northern Vietnam. The elevation of the catchment ranges between 118-482 m a.s.l. The slopes range from 20 to 60%. The catchment belongs to a larger lake catchment area of 538 ha with slopes changing gradually from 120% (~60°) to virtually 0% (0°).
The coordinates of the Dong Cao catchment are 105°29’10”E, 20°57’40”N.
Climate
The area is subject to a monsoon climate with the main precipitation falling from April to October and the 12-year (1999–2011) mean annual precipitation measured in Dong Cao catchment is 1502 mm, with a minimum of 1262 mm in 2010 and a maximum of 2506 mm in 2001.
Hydrology
The stream flow is permanent. Currently, 2 sub-catchments are monitored (w2 and w4). The catchment is bisected by a small, permanent stream which is connected to a floodplain ending in a downstream reservoir with a water storage volume of 700,000 m3.
Geology
The bedrock consists in volcano-sedimentary schists of Mesozoic age.
Soils
The soils derive from the weathering of the schists and are generally over 1.0 m deep but the range of depths highly fluctuates throughout the catchment. The dominant soil type is Acrisol (W.R.B, 2006), i.e. Ultisol (Soil Survey Staff, 1999). Soils clay content is over 50%. Soils are very porous with an average bulk density of 1.0 g cm-3. They show a homogenous brown color (10YR4/4 to 7.5 YR 4/6), and a weak vertical differentiation. The clay mineralogy is almost exclusively kaolinite with low CEC and low pH (below 5.0), and with a little difference in carbon contents.
Vegetation and land use
Until 2001, the Dong Cao catchment was covered by different crops (cassava, rice, maize, taro and peanut), some fallow and secondary forests, and some planted forest. Due to the proximity of Hanoi city, the overall land use changed progressively to degraded forest with Acacia mangium plantation and old fallow used as feeding stuffs. Nearby village also more and more encroaches on the vegetation.
The lush vegetation in Dong Cao can be watched here (November 2017, 00’54”).