To develop a watershed management plan for protection of the lake water quality, the
linkages among land use activities, stream water quality, and lake water quality must be
understood. This study conducted to develop a Decision Support System(DSS) for the reservoir
water quality managers and a comprehensive watershed management plan. This DSS has three
main components; database, interactive decision model, and data delivery interface system.
Graphic User Interface(GUI) was developed as the interface medium to deliver the data and
modeling results to the end users. Water quality management scenarios in Yongdam reservoir
consist of two parts. One is the watershed management, and the other is water quality
management in the reservoir. The watershed management scenarios that were evaluated
include as follows : a removal of point sources, control of waste water treatment plant,
reductions in nonpoint sources, and the management of developed land. Water quality
management scenarios in the reservoir include to install a curtain wall and to operate an algae
removal system. The results from the scenario analysis indicate that the strategy of the reservoir
water quality management can promise the best effectiveness to conserve the quality of
reservoir water. It is expected that many local agencies can use this DSS to analyze the impact of
landuse changes and activities on the reservoir watershed and can benefit from making
watershed management decisions.