DISTRIBUTION CHARACTERISTICS OF THE ANNUAL NITROGEN LOAD IN YAMATO RIVER BASIN IN 2011

Abstract

Although there was not enough data to calculate the amount of nitrogen load in the Yamato
River basin, some estimation methods were applied for calculation. The estimation of flow rate was made
using a calculation of the cross section and velocity using a new method to estimate velocity from cross
section and water level values based upon the modified Manning equation. The estimation of total nitrogen
concentration was calculated using EC and water level values or flow rate. As a result, the annual total
nitrogen load at Kashiwara, Fujii, Itahigashi, Hota, Shintatsuta, Nukatabetakabashi, and Kamihanda stations
and the Nara sewage treatment plant were estimated to be 1856, 1793, 751, 498, 260, 188, 83 and 481t/year
in 2011. The amounts of total nitrogen load from two sewage treatment plants reached 900t/year, about 45%
of those at the Yamato River basin. The annual total nitrogen load at Kashiwara Station under flood
conditions with over 24m3
/sec of flow rate and excluding flood conditions were calculated to be 835 and
1021t/year in 2011. The annual total nitrogen load at Fujii Station was calculated to be 1013t/year under
flood conditions with over 22m
3
/sec of flow rate and excluding flood conditions to be 780t/year in 2011.