Application of Margin of Safety Considering Regional Characteristics for the Management of Total Maximum Daily Loads

Abstract

The allocation of margin of safety (MOS) at a uniform rate to all areas of the unit watershed makes it very difficult to keep the load allotment stable in the area for lack of reduction measures like forest land. This study developed an equation to calculate margin of safety differentially according to the regional characteristics. The equation was formulated on the basis of the regional characteristic factors such as a load contribution factor for land use type and a site conversion factor for the unit watershed. The load contribution factor represents a contribution of loads from a particular land use. The site conversion factor was derived from the site conversion ratio of a unit watershed. Margin of safety for the non-point pollution load in the land use sector decreased by 20~25% in three river basins. The margin of safety in the unit watersheds with low site occupation ratios decreased in high rate, while in the unit watersheds with large urban area decreased in low rate. With the application of the differential margin of safety considering regional characteristics, not only the reduction of pollution loads can become lighter but also it can be easier to develop plans for Total Maximum Daily Loads (TMDLs) even where the reduction measures are not available.

Development of Daily Flow Expansion Regression and Web GIS-Based Pollutant Load Evaluation System

“…Advantages Limitations [14] Insufficient data updated using the daily data at a nearby, hydrologically similar gauging station Insufficient evaluation of hydrologically similar observation points [12,15] Flow data estimated using TANK model with respect to sampling frequency Estimated data affected by various artifacts (e.g., a dam) located near the study area [10,16] Extended daily flow data from 8-day interval flow data using SWAT model High-flow regime faces high uncertainty due to scarce high-flow measurements [17][18][19][20][21][22] Emphasizes the advantages of daily discharge data for constructing FDCs and the importance of daily timestep hydrological information for water resource management However, due to the construction of various artifacts, such as weirs, reservoirs, and agricultural waterways, the hydrological modeling is facing difficulties that result in uncertainties. Thus, a study on the development of the daily flow expansion regression equations employing the 8-day interval measurement data in the monitoring networks has been implemented to evaluate the annual pollutant load characteristics for flow conditions [7]. However, the regression equations of the daily flow expansion developed through previous studies have disadvantages due to the fact that these equations do not accurately reflect the continuously changing streamflow characteristics.…”

“…To evaluate the achievement of the target water quality in TMDLs, the water quality data measured at an average of 8-day intervals for a certain period are averaged and compared with the target water quality. Also, the flow duration curve (FDC) and the load duration curve (LDC) have been used to evaluate the achievement, which was developed in the US Environmental Protection Agency (EPA) to establish a total pollution management plan [4,6,7]. Recently, in a total water pollution management system at a tributary, the LDC tool has been widely used for managing the total pollutant load in watersheds.…”