Download A Simplified Model for Long Term Prediction on Vertical Distributions

A Simplified Model for Long Term Prediction on Vertical Distributions of Water
Qualities
in Lake Biwa
Hosoda, T.(1) and Hosomi, T.(2)
(1) Dept. of Civil Engineering, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan;
[email protected]
(2) Technical Official, Osaka Municipal Office, 1-3-20, Nakanoshima, Kita-ku, Osaka,
530-8201, Japan
Abstract
This paper describes a one-dimensional simplified model to predict the vertical
temperature and water quality distributions through a year in Lake Biwa, which is the
largest lake in Japan, using the monthly averaged meteorological data. The temperature
and flow velocity equations the thermodynamic exchange at a water surface were firstly
tested to calculate seasonal variations of temperature distributions in the vertical
direction. It is shown that the typical patterns of temperature distribution with
stratification and de-stratification processes can be reproduced numerically through a
year, if thermal convection during the period of heat radiation is considered in a 1-D
simplified model.
Then the water quality parameters such as Phytoplankton (Chlorophyll a), Zooplankton,
Organic and Inorganic nutrients, DO are combined with the water temperature prediction
model, using a standard modeling of ecological processes. The long term calculations
were carried out for ten years, and the results show the periodic year-by-year changes,
because the inorganic nutrients are supplied due to the release from sediments. The
limitation on Inorganic Phosphorus during a summer can be simulated in a surface layer
in calculated results, and Inorganic nutrients in a epilimnion are supplied from a
hypolimnion by both the thermal convection in an autumn and the large eddy diffusivity
in a winter because of no-stratification. (A part of calculated results are shown in
Figures.)
Since it was shown that the calculated water quality distributions agree with the
observed ones qualitatively, the model was applied to simulate the response of water
quality parameters to the global warming. It was pointed out that when air temperature
increases 3  C, DO concentration will be almost 0 at a bottom layer in the lake.
-----------------------------------Takashi Hosoda,
Dept. of Civil Eng., Kyoto University
e-mail: [email protected]