Transcript Slide 1
Watersheds • Reading: – Discussion: issues facing Arizona’s rivers • Lecture: – How you identify a watershed – Why are they important • Activity: – Using tributaries to find a watershed boundary HWR203 The University of Arizona Washburne What separates watersheds? How do you identify watershed boundaries? River Networks Contour Lines Drainage Divides Reynolds and Johnson boto.ocean.washington.edu/gifs/purus.gif HWR203 The University of Arizona Washburne Drainage Divide Drainage Basin • A region or area bounded by a drainage divide and occupied by a drainage system; • specifically, the tract of country that gathers water originating as precipitation and contributes it to a particular stream channel or system of channels, or to a lake, reservoir or other body of water. • The original meaning of the term signifies a “water parting” or the line, ridge, or summit of high ground separating two drainage basins. Source: Glossary of Geology, 3rd Ed.,1987, AGI HWR203 http://www.alpinezone.com/hiking/01images/older/KNIFEDGE.jpg The University of Arizona Washburne Watershed Definitions • A region draining into a river or lake (American Heritage Dictionary) • The area that produces runoff to a downstream point (Handbook of Hydrology) • The area contained within a drainage divide above a specified point on a stream (Dictionary Of Geologic Terms) • The upstream area that can contribute runoff to a point below. • A drainage basin that divides the landscape into hydrologically defined areas. (Environment Canada) HWR203 The University of Arizona Washburne The Continental Divide is a line separating waters that flow into the Atlantic Ocean or Gulf of Mexico from those that flow into the Pacific Ocean. It runs north-south along the crest of the Rocky Mountains (in Mexico and Canada too) and is sometimes called the Great Divide. This map layer was compiled by the U.S. Geological Survey by extracting the appropriate lines from the Hydrologic Unit Boundaries layer of the National Atlas. http://www.nationalatlas.gov/Images/condivm.gif HWR203 The University of Arizona Washburne www.nationalatlas.gov/ condivm.html Watershed - Importance 1. Understand what a watershed is both literally and conceptually (including the mapped representation of a watershed and the issue of scale). 2. Understand the components and processes of a watershed including runoff, soil, geology, geography, permeability, storage, land cover, land use, vegetation, precipitation, stream flow, flooding, drought (climate), fire, drainage patterns, erosion, deposition and population. 3. Understand a watershed as a system (e.g. a change in one area will affect the dynamics of the entire system) and how that system functions. 4. Understand that watershed management is complex because of culture, economics, politics, social constructs, scientific studies and aesthetics. Some water users include urban, rural, agricultural, business & industry, energy, recreation, fish and wildlife and earth systems. 5. Understand that watersheds change over time both naturally (e.g. flooding, fire) and due to anthropogenic causes (e.g. damming a river, water rights, water withdrawals). 6. Know some of the issues facing the watershed managers of the Colorado River Watershed as well as other Southwestern Watersheds. HWR203 The University of Arizona Washburne The drainage pattern allows you to understand the watershed boundaries and directions of stream flow even without topography The University of Arizona Washburne … although a shaded DEM helps! The University of Arizona Washburne Seeing Watersheds Activity 1: trace the main channel of the river from its mouth to the headwaters. 2: trace the major tributaries (start at the coast/Gulf). 3a: Find the drainage divides by marking a dot above the top of each river, midway to the adjacent watershed. 3b: Connect the dots (start at the mouth) to form the watershed boundary. 4:Identify sub-watersheds of major tributaries HWR203 The University of Arizona Washburne Synonyms: Basin Catchment Catchment Area Catchment Basin Drainage Area Drainage Basin Feeding Ground Gathering Ground Hydrographic Basin Watershed Source: Glossary of Geology, 3rd Ed.,1987, American Geophysical Institute HWR203 The University of Arizona Washburne Watershed – Sub-watershed HUC: 14-15 HWR203 HUC: 1401-1508 The University of Arizona Washburne Colorado – “source” of 4 WS’s = 8,131,000 af HWR203 The University of Arizona Washburne Major Western Rivers Strahler: 4-7 HWR203 The University of Arizona Washburne Major Western Rivers ag.arizona.edu/watershed/ Columbia Klamath Yellowstone Snake Sacramento Platte San Joaquin Gila HWR203 Rio Grande The University of Arizona Washburne Contributing Area Upper Basin • CO • WY • NM • UT Lower Basin • AZ • NV • CA HWR203 The University of Arizona Washburne CRB Analysis HWR203 The University of Arizona Washburne