Assessment of factors influencing groundwater-level change using groundwater flow simulation, considering vertical infiltration from rice-planted and crop-rotated paddy fields in Japan

Iwasaki, Yumi; Nakamura, Kimihito; Horino, Haruhiko; Kawashima, Shigeto

Assessment of factors influencing groundwater-level change using groundwater flow simulation, considering vertical infiltration from rice-planted and crop-rotated paddy fields in Japan | Évaluation des facteurs influençant les variations piézométriques en utilisant des simulations des eaux souterraines considérant l’infiltration verticale à partir de rizières associant riz et céréales en rotation au Japon. Evaluación de los factores influyentes en el cambio de nivel de agua subterránea usando simulación del flujo de agua subterránea, considerando la infiltración vertical a partir de arrozales con plantaciones de arroz y cultivos rotados en Japón 考虑日本水稻和农作物轮作的水田垂直入渗,采用地下水流模拟评价影响地下水位变化的因素日本における水稲作付水田と転作田からの鉛直浸透過程を考慮した地下水流動解析による地下水位に影響を与える要因の評価 Avaliação dos fatores que influenciam a alteração do nível freático utilizando a simulação do escoamento subterrâneo, considerando a infiltração vertical em campos de cultivo de arroz e a rotação de arrozais no Japão

2014

Iwasaki, Yumi | Nakamura, Kimihito | Horino, Haruhiko | Kawashima, Shigeto

Assessing factors that influence groundwater levels such as land use and pumping strategy, is essential to adequately manage groundwater resources. A transient numerical model for groundwater flow with infiltration was developed for the Tedori River alluvial fan (140 km²), Japan. The main water input into the groundwater body in this area is irrigation water, which is significantly influenced by land use, namely paddy and upland fields. The proposed model consists of two models, a one-dimensional (1-D) unsaturated-zone water flow model (HYDRUS-1D) for estimating groundwater recharge and a 3-D groundwater flow model (MODFLOW). Numerical simulation of groundwater flow from October 1975 to November 2009 was performed to validate the model. Simulation revealed seasonal groundwater level fluctuations, affected by paddy irrigation management. However, computational accuracy was limited by the spatiotemporal data resolution of the groundwater use. Both annual groundwater levels and recharge during the irrigation periods from 1975 to 2009 showed long-term decreasing trends. With the decline in rice-planted paddy field area, groundwater recharge cumulatively decreased to 61 % of the peak in 1977. A paddy-upland crop-rotation system could decrease groundwater recharge to 73–98 % relative to no crop rotation.

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