"This report is the Geomorphic and Sediment Transport Baseline Assessment Report (Chapter 3) for the Strategic Environmental Assessment (SEA) of the Hydropower Sector in Myanmar. Subsequent reports will provide an environmental vulnerability and hydropower sustainability assessment of the Business as Usual (BAU) hydropower development scenario, and recommendations and mitigation options related to sustainable hydropower development in Myanmar. This Baseline report defines the extent of the study, provides an overview of the geology and geomorphic characteristics of rivers in Myanmar, discusses how geomorphic processes can be altered by hydropower development, provides an overview of the status of fluvial (river related) geomorphic processes and a trend analysis identifying potential future changes in the absence of hydropower development. The review draws on the available literature and includes an analysis of limited flow and sediment transport data. Major findings of the review include: • Myanmar has a highly complex geologic and tectonic setting that combined with the hydrology of the region controls the ‘natural’ geomorphic processes. The distribution of older ‘hard’ mountain ranges in the north and east of the country, and younger ‘softer’ active mountain belts in the west result in sediment loads with differing characteristics being derived from the different areas of the country. Hard, resistant sands are derived from the weathering of the ‘harder’ strata, while fine-grained silts and clays are predominantly derived from the ‘soft’ strata; • Large alluvial basins are located between the mountain ranges that temporarily store sediment. These areas can provide large ‘pulses’ of sediment in response to short-duration high intensity rainfall events; • Sediment storage also occurs within the Ayeyarwady - Sittaung delta complex and along the western and eastern coastal areas where the rivers of the Rakhine and Tanintharyi, respectively, deliver sediment from the mountainous coastal areas. The stability of these areas is dependent on the continued supply of sediment from the mountains to the coastline; • The flood pulse hydrology of the rivers in Myanmar governs the movement of water and sediment through the river systems. The hydrology of some sub-basins has been altered through the development of hydropower and irrigation, and seasonal water and sediment flows at the sub-basin level have likely occurred associated with these developments and other land use changes. More detailed monitoring and analysis is required to identify potential impacts at the basin scale; The key themes related to hydropower development are the alteration of water and sediment flows associated with river regulation. The potential interaction between these changes and land use changes (mining), other water uses (irrigation), floodplain developments and aggregate extraction from rivers also need to be considered and understood for the implementation of ‘sustainable’ hydropower. Substantial data gaps have been identified during this review. These include: • A need for systematic geomorphic descriptions of the rivers at a scale that can be used to assess potential changes to rivers in response to hydropower or other water resource developments; • More detailed suspended and bedload sediment transport information is needed from subbasins and mainstem rivers to provide the required information to underpin sustainable hydropower development. This information is also required for effective management of sand and gravel mining, as well as understanding the dynamics of the river; • Detailed flow information from sub-catchments and mainstream rivers is required at a higher resolution than provided by the present network of flow gauges. This information may be able to be provided through the development of catchment hydrologic models; • Information about the characteristics of sediment moving through the system, including grainsize and mineralogy. Grain-size will allow a better understanding of what flows are required to transport sediment and mineralogy will provide information about the source of the material; vi • More information is required about how individual hydropower projects will alter flow regimes at the sub-basin level, how sediments will be managed and what mitigation strategies are to be included in the project design. A sound understanding of the project is required to understand how it will affect the upstream and downstream environments; • More information is required about other planned water resource developments that have the potential to alter flow and sediment regimes. A sub-basin and basin management approach to water resource development is required to minimize impacts and maximize outcomes; • An increased understanding of how climate change may affect the river systems is needed for long-term sustainable planning of hydropower and other water resource developments. The review has found that even in the absence of additional hydropower development there are substantial pressures on the river systems of Myanmar, related to existing hydropower projects (both in Myanmar and upstream of the border), land use changes such as mining, deforestation, sand and gravel mining, irrigation extractions, and floodplain and river modifications. Catchment management at the sub-basin scale is required to control and manage these activities, and the implementation of stringent Government policies to minimize impacts from these activities is warranted. Sustainable hydropower can only be developed within a catchment that is being sustainable managed with respect to other land use and water resource activities..."