1.   Purpose and objectives

     The tank model is a simple non-linear model that will transform precipitation into discharge for the forecasting of daily discharge or flood discharge. Once the parameters have been determined, use of the model is very easy by hand using tables or by portable desktop computer.

2.   Description

     The tank model is composed of several tanks -- usually four tanks for daily discharge forecasting and two or three for flood forecasting -- laid vertically in series. Each tank has outlets or an outlet on the side and an outlet on the bottom. Outputs through side outlets form the estimated discharge while outputs through bottom outlets simulate infiltration. The estimated discharge is composed of components from each of the tanks that corresponds to surface, intermediate, sub-base and base runoff. Rain water is distributed to each components automatically by this simple model. There 
are two program version, one for trial and error calibration, the other for  automatic calibration.

3.   Input

     (a) For daily discharge analysis :

         Daily precipitation (3 - 5 rain gauges are preferable); daily or 
         monthly mean of potential or actual evaporation; daily discharge;
         in snowy region daily maximum and minimum or daily mean temperature.

     (b) For flood analysis :

         Usually, hourly precipitation and discharge. Appropriate time unit
         Tu (hour) depends on the area of basin A (sq. km.), given
         approximately by Tu = 1/20 A.

4.   Output

     Calculated discharge.

5.   Operational requirements and restrictions

     (a) A few persons are required, who have interest and knowledge of 
         hydrology or water resources and have experience in computing.

     (b) Three months training is preferable, using preferably the data of 
         their own country.

     (c) Automatic calibration program is difficult for small computer, 
         but experiences obtained by trial and error must be much more 
         important for hydrologists.

6.   Form of presentation

     Diskette or CD with software programs. Computer program in FORTRAN IV is also presented as a listing. Program contains many comments for users. 

7.   Operational experience

     The tank model is applied not only to the basins in Japan but also to basins in Asia, Africa, Europe and U.S.A. and gives good results.

8.   Originator and technical support

     National Research Centre for Disaster Prevention
     Dr. M. Sugawara

9.   Availability

     From the HOMS National Reference Centre for Japan.

10.  Conditions on use

     Without any conditions.