Natural River Flow Sample Clauses

Natural River Flow. River waters have been continuously developed for various uses since the olden days to satisfy water use requirements in river basins. Hence, river flow regimes have historically changed according to water resources developments as well as changes of watershed conditions (land use changes such as deforestation, shifting cultivation for upland farming, etc.). Thus the current river flow regime (observed flow) is different from the past one due to the effects of the existing water uses. Basically, engineering studies for water resources development planning requires the natural river flow regime in the objective river basin as the first planning step. The natural river flow is usually defined as the river flow that is not affected by any water use and water resources development. Along this line, the design natural low flow regime (design low flow) is determined as the basis for evaluating the available surplus quantity of river water for planning. The current (observed) river flow is more or less influenced by the existing water uses such as water storage in reservoirs, water release from reservoirs, and water abstraction from rivers. A simple illustration of the relationship between natural flow and observed flow is given in the figure below. If the water stored in a reservoir is used only for hydropower purpose, then there will be an increase in dry season flows. Several explicit examples on changes in low flow regime in the Mekong River Basin are explained below. Water usage issues in the Lower Mekong Basin are of great importance for the design of the Basin Simulation Modelling Package and Knowledge Base developed by the WUP-A. This modelling package would need to naturalize the measured hydrological flows. It has however been reported that WUP-A was confronted with difficulties and constraints of the serious lack of historic water usage data (mainly relating to irrigation development) and the sparse information available for effective model calibration. In general, it might be difficult to obtain pure natural flow regimes since human activities are extensive. Hence, the historic water use data are very necessary to estimate the natural flow on the basis of the measured flows. The actual current river flow regimes of the Mekong River (observed historical records at the hydrologic stations on the Mekong mainstream) are resulting from accumulated effects of historic basin-wide water uses. Establishing “acceptable flows” based on “the natural flow regime” ...