In Korea, Total Water Load Management System have been planning and implementing to meet water quality target with the specific flow conditions.
The purpose of this study is to find the appropriate approach for the estimation of the allocations of the pollutant loads along the entire flow conditions by using watershed model(HSPF) and Load Duration Curves(LDC).
Model simulation and analysis of excess loads over the water quality target at each flow conditions were performed by the data sets of 2007 and 2010 year. Additionally, the data of 2010 was utilized to analyze the scenarios and various parameters.
First of all, the rate of excess loads from water quality target was estimated by using simulated flow from HSPF model and LDC. In case that TP was 50% probability of non-exceedance from water quality target along the entire flow rate, the loads were estimated by the delivery ratio and the application of flow fluctuation condition.
Finally, the allocation of loads was designed by the different flow conditions with the consideration of the Margin of Safety loads(MOS).
The LDC approach depends on the flow, and that maximum allowable loading would be various with flow conditions.

The results of this study were as follows.

1. As the results of calibration and validation of flow and water quality(Water temperature, DO, BOD, T-N, T-P, Chl-a) in HSPF model, the simulated values were appropriately matched with the observed values in each stream watersheds.

2. The excess rates over the water quality target were analyzed by the simulated value excluding the actual observations to ensure water quality variation according to watershed characteristics under 5 flow conditions. The excess rate of BOD was 3.0~6.0%, and T-P was exceeded by 61.2~71.2% at Naesung stream watershed. In case of the Guemho stream watershed, the excess rates presented 3.0~6.0% of BOD, 61.2~71.2% of T-P, respectively.

3. The allowable discharge loadings were calculated with 5 flow conditions that used point and non-pont delivery loadings to meet the target and the delivery ratio in baseline year.

4. To define the MOS using the LDC, the two methods are proposed. The first method was based on the difference between the loading capacity as calculated at the mid-point of each of the five flow zones, and the loading capacity calculated at the minimum flow in each zone. The second method is converted into a percentage between the loading capacity as calculated at the mid-point of each of the five flow zones and the MOS loading calculated by the first method. Because the allocations are a direct function of flow, accounting for potential flow variability is an appropriate way to address the MOS. As a result, the uncertainties in different hydrologic conditions should be established according to watershed characteristics.

5. The allocaitons was considered with different flow conditions as the allowable discharge loadings minus the MOS calculated. As a result of calculations in the mid-range conditions, the Naesung stream watershed is 1,217.75 ㎏/day, 1,018.94 ㎏/day, 1,111.64 ㎏/day, the Guemho stream watershed is 1,519.97 ㎏/day, 1,335.90 ㎏/day, 1,413.39 ㎏/day respectively.

6. This study is attempted to develop method of the Total Water Load Management System using watershed model and Load Duration Curves(LDC) considering entire flow conditions and evaluated possibility of application on calculated allowable discharge loadings, allocations and MOS loadings as applying on Naesung, Geumho stream watersheds.