Tropentag, September 19 - 21, 2012 in Göttingen "Resilience of agricultural systems against crises"

Quantification of Water Flows and Sediment Transport in Paddy Cascades in Vietnam and Representation in a Landscape-Scale Model

University of Hohenheim, Inst. of Plant Production and Agroecology in the Tropics and Subtropics, Germany

Abstract

In Vietnam, the second most important rice producer in South East Asia, most of the rice is grown on paddy terraces. These terraces modify water flow and sediment transport in sloping landscapes, holding back sediments originating in uplands fields.
The Land Use Change Impact Assessment tool (LUCIA) is a dynamic and spatially explicit model developed at the Institute for Plant Production in the Tropics and Subtropics, University of Hohenheim. LUCIA simulates consequences of land use change on watershed functions, biomass production, environmental services and soil productivity and fertility at landscape scale in small mountainous catchments. The aim of this work was to develop a module simulating the water flow and sediment transport in paddy cascades and implement it in LUCIA.
To calibrate the model field measurements were conducted 2011 in Yen Chau, Northwest Vietnam. The topography of the cascade was mapped first. Water inflow and outflow into a cascade and flow between the individual paddies were quantified using water clocks and sediment loads of the water were measured using turbidity sensors. After the rice harvest top soil samples were taken on a grid of 10 m² and analysed using Mid-Infrared-Spectroscopy (MIRS) for organic carbon, total nitrogen and texture. For MIRS- validation data from Schmitter (2009) were used.
Inflows into the cascades occur only during the rice season (when inlets are not blocked). Each cascade is seen as one tank with limited outflow through pipes or, during heavy rain events, overflow surpassing the paddy bunds. Inflows into a tank are rainfall and channel flow, while evapotranspiration, infiltration, bund flow and outflow leave the cascade. First standalone runs of the paddy module have been undertaken and the integration into the LUCIA model has been technically accomplished. Further steps include plausibility tests of the combined model.

Keywords: Landscape modelling, paddy hydrology, paddy model

Contact Address: Rebecca Schaufelberger, University of Hohenheim, Inst. of Plant Production and Agroecology in the Tropics and Subtropics, 70593 Stuttgart, Germany, e-mail: r.schaufelbergeruni-hohenheim.de