STREAM PROCESSES FOR WATERSHED STEWARDS AZ1378g AUGUST 2006 Streams Processes for Watersheds Stewards GEORGE ZAIMES Assistant Professor/Extension Specialist In Riparian Watershed and Rangeland Management ROBERT EMANUEL Senior Program Coordinator Arizona Master Watershed Steward This information has been reviewed by university faculty. cals.arizona.edu/pubs/natresources/az1378g.pdf AZ1378g August 2006 Cooperative Extension College of Agriculture and Life Sciences The University of Arizona Tucson, Arizona 85721 TABLE OF CONTENT PART I: STREAM PROCESSES Introduction........................................................................................................................................... 3 The Hydrologic Cycle .......................................................................................................................... 3 Geomorphology.................................................................................................................................... 4 Fluvial Geomorphology....................................................................................................................... 5 What Happens Before the Stream Forms .......................................................................................... 5 Stream Channel Formation ................................................................................................................. 6 Stream Reaches ..................................................................................................................................... 6 Water in the Stream Channel.............................................................................................................. 8 Dynamic Equilibrium .......................................................................................................................... 8 Human Influences on Channel Dynamics ...................................................................................... 11 The Channel Evolution Model.......................................................................................................... 11 Why is this Model Important? .......................................................................................................... 13 Life & Stream Processes..................................................................................................................... 13 PART II: STREAM CLASSIFICATIONS Introduction......................................................................................................................................... 15 Classification Based on Stream Pattern ........................................................................................... 15 Classification Based on Stream Flow Conditions........................................................................... 16 Classification Based on Stream Order ............................................................................................. 16 Classification by Rosgen.................................................................................................................... 17 Special Stream Types of the Southwestern U.S. ............................................................................. 20 Stream Functional Zones................................................................................................................... 20 The River Continuum Concept......................................................................................................... 20 Some Final Thoughts.......................................................................................................................... 22 Words to Know................................................................................................................................... 24 Sources ................................................................................................................................................. 28 Stream Processes Publication # AZ1378g The University of Arizona Cooperative Extension 2 PART I: STREAM PROCESSES George Zaimes & Robert Emanuel “Water is the eye of a landscape.” –Vincent Lean, Collectanea, 1902 INTRODUCTION In this part you will learn about: Streams are natural linear configurations in the Basic terms related to streams. land surface that transport water and sediment. Basic terms of fluvial geomorphology. They are characterized by water moving under The process of stream formation & evolution. the influence of gravity that flows through defined Stream impacts on aquatic life. channels to progressively lower elevations. Streams are one of the most readily identifiable features of the landscape. Looking down from an These fields explain stream processes and how airplane you may be able to pick them out of the and where water moves before it reaches the landscape as winding, twisting or straight lines stream. that tend to branch off and eventually become smaller and smaller toward the higher elevations THE HYDROLOGIC CYCLE of a watershed. From an aerial view you may also be able to identify their end points in lakes, The hydrologic processes that redistribute water reservoirs, larger rivers or oceans. through the oceans, atmosphere and land can be described by the hydrologic cycle (Figure 1). Before explaining more about streams it is Water in stream channels originates from essential to understand the broader sciences of precipitation, overland flow, subsurface flow, and geomorphology and fluvial geomorphology. groundwater flow. Figure 1. The hydrologic cycle is the movement of water between land, streams, oceans and the atmosphere. This cycle involves many numerous pathways and major storage units such as soils, aquifers, oceans, atmosphere and plants. Water is not created or destroyed (Illustration by D. Cantrell). Stream Processes Publication # AZ1378g The University of Arizona Cooperative Extension 3 Precipitation includes the water that condenses IMPORTANCE OF STREAMS into droplets or ice crystals and falls to the ground. Various forms include: rain, snow, hail, Streams are often the focus of the landscape freezing rain, and fog drip. Evaporation is the and the watershed. While the watershed loss of water as vapor from surfaces such as captures and defines the water movement in streams, lakes, puddles, ponds and soil pores. the landscape, the stream transports water Transpiration is the loss of water as vapor from across the watershed. In addition to water, plant pores. Often evaporation and transpiration the stream also recruits and transports are combined into the term evapotranspiration. sediments. The transportation of water and Sublimination of snow is another way water sediment is the major function of streams. returns to its vapor phase. Finally, the storage of water in the watershed includes various Naturally, wildlife and humans are very locations where the water is retained temporarily attracted to, and in arid regions dependent before it is evaporated, transpired, or moved to upon streams. Many flora also prefer the outlet of the watershed. Water flow in the locations near stream courses. Land areas watershed is delayed by being stored in the soil’s adjacent to streams are called riparian ar- unsaturated and saturated zones. eas. These areas have distinctive vegetative, soil and hydrological characteristics com- In addition, surface soil depressions, vegetation, pared to the watershed uplands or other drier other living organisms, as well as puddles, lakes, sites because of their proximity to higher constructed reservoirs, wetlands or the stream amounts of water. In Arizona, 90% of all ver- channel itself can act as significant sources of tebrates spend some portion of their life in stored water. The amount of precipitation that a riparian areas. In addition, 70% of threatened watershed receives depends on a number of and endangered Arizona vertebrates depend factors, including local climate, longitude and on riparian habitat. latitude, altitude, as well as proximity to the Reduction, alteration or elimination of the ocean. Evaporation is heavily dependent on amount of water in streams has major im- temperature and is influenced by the same pacts on the riparian vegetation and fauna. factors as precipitation. Transpiration depends Finally, most major cities and towns in Ari- on the amount and kind of vegetation and the zona and the rest of the United States are growing season. Lastly, evapotranspiration located near a stream or some significant depends upon the combination of temperature, source of surface water. precipitation and vegetation characteristics or season. GEOMORPHOLOGY If precipitation exceeds evapotranspiration then water will be stored (maybe temporarily) in the Geomorphology is the branch of geology watershed in one of the locations mentioned dealing with the origin, evolution and previously. Infiltration is the process of water configuration of the natural features of the earth's entering the surface of the soil. Infiltration is surface. It originates from the Greek words geo, influenced by vegetation cover, soil surface which means earth, and morphology, which roughness and soil subsurface conditions (soil refers to the scientific study of form and structure. structure, texture, moisture and organic matter Geology is the science of rocks, mountains and content) as well as topographic characteristics. valleys—the basic foundations of watersheds. High rates of infiltration will lead to more water Most geologic development is controlled by entering the soil profile, more