Landform transformation on the urban fringe of Bangkok: The need to review land-use planning processes with consideration of the flow of fill materials to developing areas

For large Asian cities situated on deltaic lowlands, landform transformation is essential for both agrarian and urban development. Understanding landform transformation processes and patterns is important for landscape planning in areas of mixed urban–rural land use on the periphery of these cities. We examined landform transformation processes and patterns in Bangkok at three scales: (1) meso-scale quantitative landform analysis on the urban fringe of Bangkok using aerial photograph interpretation and topographic measurements; (2) micro-scale field measurements in sample districts to investigate relationships between building styles and the types of fill material used; (3) macro-scale analysis of the flow of fill material from source areas outside Bangkok to end use on the urban–rural fringe of the city. Our study showed that the type and the cumulative volume of fill material used are related to past agricultural land-use patterns, which in turn are related to the pre-existing natural local environment. We found associations between building styles and types of fill material used: townhouses are built on clay fill foundations, whereas condominiums and roads with heavy traffic loads are built on sand fill. Each type of fill has a different flow from source to end use that is influenced by geologic and economic conditions. The flow of clay fill is limited to the meso-scale urban fringe area, whereas sand fill travels from sand pits on a natural sand levee 100 km upstream from its end use on the urban fringe. The sand output at its source was estimated to be 1.5 × 105 m3 day−1, which, depending on cost, is either trucked or transported by river to the urban fringe development areas. Thus, landform transformation was found to occur at multiple scales in the Bangkok region, and the delta is no longer flat. These findings suggest that deltaic landscape planning should incorporate the means of managing the flow of fill material from source pits to end use in urban fringe development areas.