The Pasak Jolasid Dam Project, which is the project initiated by His Majesty the King, has a major role in mitigating floods and droughts in both the Pasak and the Lower Chao Phraya river basins. To enable the Project to operate in such a way to obtain optimum efficiency and effectiveness, “the Assessment of Pask Jolasid Dam Project” was initiated with the objectives to monitor the actual operation in accordance with various objectives, to identify difficulties and impacts as well as to compile information necessary for the improvement of the Project’s operation. This Research Project which covers the areas in the Pasak and the lower Chao Phraya, from the periods at the starting of the dam construction up to the present and forecast into the future for the next 20 years, and with the following objectives: 1. To evaluate the effectiveness and the operation and management of the Project in accordance with all objectives as stated in the Project Feasibility Report; 2. To evaluate the impact(s) upon groundwater due to the development of the Project; and 3. To provide suggestions on ways and means to improve the Project’s water management in accordance with the Project’s objectives. The compilations and the analyses comprise of the following topics: 1. Surface water, flood mitigation, tele-metering system 2. Irrigation, water allocation and reservoir operation/management 3. Groundwater resources 4. Water utilization and water demand. The Study which analyzed and considered various alternatives for improvement of water management under existing/current situation and further elaboration on studies and researches to develop the analytical tools and to incorporate the outputs for water allocation. The conclusion and suggestions for improving the project’s management comprise of the followings: 1. The system development of the water demand assessment 2. The improvement of inflow into the reservoir forecasting technique 3. The operation rule curves of the reservoir 4. The conjunctive uses among surface and subsurface water 5. The prioritization and water allocation guideline 6. Suggestion on the improvement of agriculture in the irrigation areas 7. Innovative(s) in the future water management.