Watersheds • Reading: – Table groups: discussion questions about issues facing Arizona’s rivers Watersheds • Lecture: – HidtifthdHow you identify a watershed – Why are they important “A river is the report card for its – Simple unit conversions watershed.” — Alan Levere • Activity: – Using tributaries to find a watershed boundary – Estimating volume Arizona Water Issues © 2010 The University of Arizona – HWR203 1 Arizona Water Issues © 2010 The University of Arizona – HWR203 2 Drainage Divide What separates watersheds? Drainage Basin How do you identify watershed boundaries? • 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 particu lar s tream c hanne l 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 River Networks line, ridge, or summit of high Contour Lines ground separating two drainage Drainage Divides Reynolds and Johnson basins. boto.ocean.washington.edu/gifs/purus.gif Source: Glossary of Geology, 3rd Ed.,1987, ©AGI 2010 The Universityhttp://www.alpinezone.com/hiking/01images/older/KNIFEDGE.jpg of Arizona – HWR203 Arizona Water Issues © 2010 The University of Arizona – HWR203 3 Arizona Water Issues 4 The Continental Divide is a line separating waters that flow into Watershed Definitions 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 • A region draining into a river or Mountains (in Mexico and Canada too) and is sometimes called the Great Divide. lake (American Heritage Dictionary) This map layer was compiled by the U.S. Geological Survey by extracting the • The area that produces runoff appropriate lines from the Hydrologic Unit Boundaries layer of the National Atlas. 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 http://www.nationalatlas.gov/Images/condivm.gif hydrologically defined areas. (Environment Canada) Arizona Water Issues © 2010 The University of Arizona – HWR203 5 Arizona Water Issues © 2010 The University of Arizona – HWR203 6 www.nationalatlas.gov/ condivm.html 1 The drainage pattern allows you to understand the watershed Watershed - Importance boundaries and directions of stream flow even without topography 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 difthtit)dhthttftidynamics 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. Arizona Water Issues © 2010 The University of Arizona – HWR203 7 Arizona Water Issues © 2010 The University of Arizona – HWR203 8 … although a shaded DEM helps! 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 byyg 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 Arizona Water Issues © 2010 The University of Arizona – HWR203 9 Arizona Water Issues © 2010 The University of Arizona – HWR203 10 Synonyms: Watershed – Sub-watershed Basin Catchment Catchment Area Catchment Basin Drainage Area Drainage Basin Feeding Ground Gathering Ground Hydrographic Basin Watershed HUC: HUC: 14-15 1401-1508 Source: Glossary of Geology, 3rd Ed.,1987, American Geophysical Institute Arizona Water Issues © 2010 The University of Arizona – HWR203 11 Arizona Water Issues © 2010 The University of Arizona – HWR203 12 2 Colorado – “source” of 4 WS’s Major Western Rivers Strahler: = 8,131,000 af 4-7 © 2010 The University of Arizona – HWR203 Arizona Water Issues 13 Arizona Water Issues © 2010 The University of Arizona – HWR203 14 Colorado River Watershed before 1921 Major Western Rivers ag.arizona.edu/watershed/ Green River Columbia Yellowstone Snake Grand River Klamath Sacramento Platte San Joaquin Colorado River Rio Gila Grande Musser, 2005. Arizona Water Issues © 2010 The University of Arizona – HWR203 15 Arizona Water Issues © 2010 The University of Arizona – HWR203 16 Colorado River Watershed after 1921 How to determine Green River headwaters? •Hydrology –larger drainage area GrandColorado River River •Green River drains larger area •Politics –who Colorado River wants it more •CO Legislature wanted river to begin in CO Musser, 2005. Arizona Water Issues © 2010 The University of Arizona – HWR203 17 3.