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3 Watershed Basics This chapter provides an overview of the main natural and social science disciplines and the main types of issues that come up during a watershed assessment. It discusses the watershed as a whole, as well as its component parts. Just as watersheds are naturally integrated, watershed assessments are interdisciplinary in nature. This means that components analyzed separately need to come together through integration and synthesis, as described in a later chapter. Chapter Outline 3.1 Geography 3.2 Hydrology 3.3 Climate 3.4 Flooding and Stormwater 3.5 Geology, Soils, and Sediment in Watersheds 3.6 Water Quality 3.7 Aquatic Ecosystems 3.8 Terrestrial Landscape and Habitats 3.9 Human Land Uses 3.10 Water Management and Uses 3.11 Social and Economic Setting 3.12 Historic Context and Analysis 3.13 References ___________________________________ 3.1 Geography Geography—the distribution of plant, animal, and human communities across a watershed—is integral to landscape and watershed assessment. Geography also encompasses the relationships among a landscape’s processes (e.g., fire and human development) and features (e.g., vegetation types and dams). Underlying processes involving geological formations, hydrologic flows, and ecological transformation result in the presence of particular features, such as soil and plant types. Changes in the processes result in changes in the distributions of these features. Geographic investigations show that people tend to aggregate around certain features of their environment. For example, many towns have grown up around the intersections of roads, year-round waterways, coastal bays, and fertile agricultural areas. At these locations, people engage in various types of social and economic interactions that may be dependent on or independent of their surroundings. These interactions are the subject of human geography. A common tool in geography is a geographic information system (GIS), which can be available as