A case study of flood risk transfer effect caused by land development in flood-prone lowlands

Many researches mention the land development in the watershed increases the peak flow rate and volume of the surface runoff. However, another phenomenon, the land development in the lowlands with filling method probably results in flood risk transfer effect, is rarely mentioned. This study took Heshunliao Farm as study object and used SOBEK model to assess the phenomenon. The terrain of this farm was flat and low, at an elevation of about 1.3-3 m before development. A filling method has been adopted to raise the surficial elevation in the development zone to 3-5 m. The western end of the development zone is still maintained its original elevation. The storm sewer system, detention basin, and pumping stations have been built in the development zone. There are two effects in the development of the low-lying land. One is the increase in the peak outflow rate in the development zone. Under a 10-year return period rainfall, the peak outflow rate after development has increased to 9.94 cm, compared to 2.62 cm when there was no development. Another effect is that the disappearance of the original flood-accumulated space due to land development activities transfers the risk of flooding to the surrounding land. Under a 10-year return period rainfall, the flooded area of the developed area was reduced from 78.4 ha before land development to 0.32 ha after the development, while the flooded area of the western end of the development zone increased from 13.28 ha before development to 27.20 ha after development.