Urbanization can be significantly affected the hydrologic cycle by increasing flood discharge and heat flux. In order to mitigate these modifications in urban areas, Low Impact Development (LID) technique has been designed and applied in Korea. In order to estimate runoff reduction rate using SWMM LID model, the characteristics of five LID techniques was firstly analyzed for water balance. Vegetated swale and green roof were not reduce flood discharge nor infiltration amount. On the other hand, porous pavement and infiltration trench were captured by infiltration function. The flood reduction rate with LID is substantially affected by their structures and properties, e.g., the percentage of the area installed with LID components and the percentage of the drainage area of the LID components.

Phosphorus and nitrogen loadings from the main tributaries into the Nakdong River were estimated by measuring phosphorus and nitrogen concentration in the main tributaries, Nakdong River(Kangjung), Kumho River, Heichun, Hwang River, Nam River, Milyang River, and Yangsanchun from May 1994 to October. Total phosphorus concentration of Kumho River was vary high, average 1.0 ㎎P/ℓ. The other rivers were the range 0.05∼0.15 ㎎P/ℓ. Total nitrogen concentration of Kumho River was vary high, average 6.27 ㎎N/ℓ. The other rivers were the range 1.5∼3.0 ㎎N/ℓ. The phosphorus loading from Kumho River, Nakdong River(Kangjung), Nam River, Milyang River, Hwang River, Yangsanchun, and Heichun were calculated to be 1,108, 603, 198, 57, 34, 23, and 21 tP/yr, respectively. Therefore, the loading from Kumho River accounted for 45 % of total loading, 2,042 tP/yr. The nitrogen loading from Nakdong River (Kangjung), Kumho River, Nam River, Milyang River, Hwang River, Heichun, and Yangsanchun were calculated to be 12,636, 7,411, 2,611, 1,523, 779, 608, and 391 tN/yr, respectively. Therefore, the loading from Nakdong River(Kangjung) and Kumho River accounted for 50 % and 30% of total loading, 25,959 tN/yr, respectively.