Abstract
A distributed water quality tank model was developed for the evaluation of the amount of the nitrogen removal by topographic sequence in the A10 basin, where the load from livestock farms is large, within Kitaura basin, the Kasumigaura watershed, Japan. A field investigation was conducted to collect the data for land use, water quality, and runoff. The study area was divided into a 50 m×50 m grid, and elevation, land use, and drainage were set as the grids attributes. A distributed water quality tank model was comprised of grid based water quality tank sub-model. After calibration, although the relative errors were large when there was no rain during the evaluation period, the relative errors were 9% for runoff and 2% for T-N concentration during the simulation period. For the purpose of a nitrogen removal by the appropriate allocation of artificial wetlands, a trial calculation for T-N concentration and nitrogen load removal was conducted given changes in the location of the artificial wetlands. As a result, T-N concentration was decreased by 4% in the case of valley head allocation for wetlands and by 18% when wetlands were allocated where the number of cumulative grids for water to pass was largest.
