Riparian Ecology (Belonging to or relating to the bank of a river) TERMS – Riparian – Corridor – Watershed – Thalweg – Scarp – Pool – Riffle – Channel Hydrologic Cycle Surface Runoff  Runoff dependent on: – Nature of the Soil – Degree of slope of the surface – Development and type of vegetation – Local climate – Volume and intensity of experience (ppt) RESULTS  Erosion  or  Deposition WATERSHED  Define as: – An area of land that drains water, sediment, and dissolved materials to a common outlet at some point along a stream channel.  Patterns – Topography and underlying geology  Strahler’s system  Shreve’s system  http://ccl.northwestern.edu/netlogo/models/r un.cgi?GrandCanyon.854.674 Continental Divide and Mississippi Drainage Typical Drainage Patterns uniform lithology volcanic or domed uplifts fractured rocks alternating strong vs. weak rocks Moving Water Ecosystem  Relationship to the motion of the system – Rate of Flow:  volume of water passing any given point m3/sec ft3/sec – Stream Velocity:  Speed at which water moves m/sec Stream Discharge Defined Volume of water that flows past a given point per unit time Discharge (cfs) = average stream width (ft) • average depth (ft) • average velocity (ft/sec) Example: Stream dimensions are 100 ft wide and 15 ft deep Flowing at 6 ft/sec (4 mph) has a discharge of 9000 cfs Humid climates discharge typically increases downstream: 1) Water flows into stream from ground 2) Tributaries are added downstream Regions of Maximum Velocity Flow  Types – Turbulence or irregularity of motion of the water particles  Laminar flow – Perfect even  Turbulent flow – Highly irregular – http://highered.mcgrawhill.com/sites/0072402466/student_view0/chapt er10/animations_and_movies.html# Velocity vs. Grain Size Giant Boulders; Moved During Floods Classification-streams  1. Perennial – Surface flow throughout the year, only dry during periods of drought 2. Intermittent Surface flow only at certain times of the year, when it receives water from springs, snowmelt, surface run-off 3. Ephemeral Surface flow only in direct response to ppt Channel Formation Channel Development  Result of: – Geology – Fault zones – Stream flow & sediment load Channel Roughness Smooth, semi-circular channel yields highest velocity Wide, shallow channel increases friction Rough channel also slows river at base Channel Width and Obstructions Width change due to Strength change Channel narrows -> increases stream velocity  Channels – Most of the time appears that large channels are overdesigned for their discharge – Most of the year low half of channel capacity – Therefore overall stream power that they are incapable of eroding and transporting much sediment Stream Valley Development     Downcutting and Base Level The Concept of a Graded Stream Lateral Erosion Headward Erosion and Stream Piracy Stream Base Level Downcutting: Process of deepening a stream valley by erosion of the stream bed. Evolution from narrow slot to wider V-shaped valley. Base Level: Defined as the limit of downcutting for a stream. Changes in base level alter the dynamic equilibrium of the system. Ungraded vs. Graded Streams Graded stream: Balance between transport capacity and sediment load. Maintained by altering the shape of the channel and stream profile. Graded Streams  Dynamic equilibrium: – Balance between sediment load and transport capacity  Increased stream gradient: – Increases velocity, which allows the stream to carry more sediment and larger particles. This causes more erosion lowering the gradient.  Change in sediment load: – Decrease load, can cause erosion, again tending to lower the gradient. Common downstream of dams. Response of system is NOT always predictable! Lateral Erosion by Undercutting Stream Landforms • Stream Terraces • Incised Meanders • Superposed Streams Stream Terraces - Jackson Hole, WY Stream Terrace Model Bankfull Stage  Stage occurs when discharge fills the entire channel cross section without significant inundation of the adjacent floodplain. Bankfull Stage  Stage occurs when discharge fills the entire channel cross section without significant inundation of the adjacent floodplain. example Stream Erosion  Hydraulic Action  Stream Transportation of Sediment – Dissolved Load – Suspended Load – Bed Load  Transportation Mechanisms – Traction – Saltation Hydraulic Action Niagara Falls Hydraulic Action! Stream Sediment Loads Sediment Load Animation Stream Deposition       Bars Braided Streams Meandering Streams and Point Bars Flood Plains Deltas Alluvial Fans Deposition and Erosion of River Bars Normal Flow Flood: Increased discharge and erosion! Post-flood; new bars deposited Braided Streams Gravel Bars Braided Stream - Petrified Forest From: http://geoweb.tamu.edu/RGallery/zion2003/six/6c.htm Placer Deposits Oxbow Lake Development INCREASING TIME Stream Meanders & Oxbow Lakes Point Bar Development Animation Goosenecks of the San Juan River, UT Photo credit: Synaptic Gallery Incised Meanders Superposed Streams Erosion and downcutting through young horizontal units Folded Units Development of water gap Internal Delta Morphology Alluvial Fans Photo credit: National Park Service Badwater Canyon Alluvial Fan Death Valley, CA Flooding     Urban Flooding Flash Floods Controlling Floods The Great Flood of 1993 1997 Flood Floated House Effect of Urbanization on Discharge Levee Break - Cosumnes River Flash Floods in Colorado Flash Flood Effects Big Thompson Canyon, CO - 1976 Flash Flood Effects Spring Creek - 1997 Fort Collins, CO
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