© 2007, John Wiley and Sons, Inc. Physical Geography by Alan Arbogast Chapter 16 Fluvial Systems and Landforms Lawrence McGlinn Department of Geography State University of New York - New Paltz

© 2007, John Wiley and Sons, Inc. Fluvial Systems and Landforms Overland Flow & Drainage Basins Hydraulic Geometry & Channel Flow Fluvial Processes & Landforms Human Interactions with Streams

© 2007, John Wiley and Sons, Inc. Overland Flow Perennial Streams – water runs all year Ephemeral Streams – water runs only part of year Sources of stream water: Groundwater Melting Ice Surface Runoff

© 2007, John Wiley and Sons, Inc. Drainage Basins Drainage Basin – area contributing groundwater and runoff to a stream – also called Watershed Drainage Divide – elevated terrain forming rim around a drainage basin Water flows from Tributaries high in basin to Trunk Stream, largest stream in basin core Drainage basins vary tremendously in size Basins are nested, smaller within larger

© 2007, John Wiley and Sons, Inc. Small, Nested Drainage Basins

© 2007, John Wiley and Sons, Inc.

Major US Watersheds Mississippi River Basin in Bold

© 2007, John Wiley and Sons, Inc. Drainage Patterns Dendritic – uniform rock structure Rectangular – jointed & faulted rock Trellis – extreme fold- ing of rock layers Radial – rounded upland like volcano

© 2007, John Wiley and Sons, Inc. Drainage Density Total length of all streams Drainage Density = Area of drainage basin

© 2007, John Wiley and Sons, Inc. Stream Ordering Represents stream size Smallest streams in basin order 1 – order rises when 2 streams of same order come together at confluence The Rhine River

© 2007, John Wiley and Sons, Inc. Hydraulic Geometry Geometric attributes of river channels Variables: w = channel width d = channel depth v = velocity of water s = slope (steepness) also called gradient Q = discharge (amt of water flowing) Q = w x d x v (units m 3 /s or ft 3 /s)

© 2007, John Wiley and Sons, Inc. Hydraulic Variables

© 2007, John Wiley and Sons, Inc. Stream Hydrograph Rappahannock River, VA Graph showing fluctuation in stream discharge over time Lag between storm event and highest discharge Base flow – flow rate sustained by groundwater influx

© 2007, John Wiley and Sons, Inc. Flooding Flood Stage – stream discharge increases so that water spills out of channel onto adjoining ground Return Period – time between events of a given magnitude, e.g. annual flood, 50-year flood, 100- year flood Larger floods occur less frequently

© 2007, John Wiley and Sons, Inc. Flood Frequency Data Skykomish River – Goldbar, WA

© 2007, John Wiley and Sons, Inc. Mississippi River Floods At least 100-year flood, perhaps a 500-year flood Heavy winter rains saturated ground Stationary high pressure in Southeast in summer, blocking midlatitude jet stream over Midwest Cool, dry air collided with warm, moist air along jet stream, creating constant precipitation Precip ran off into stream channels & rivers

© 2007, John Wiley and Sons, Inc. Mississippi River Floods

© 2007, John Wiley and Sons, Inc. Fluvial Processes and Landforms Running water is most important geomorphic (landform shaping) process on Earth’s surface All landforms due to either erosion or deposition Erosional landforms occur when sediment, soil, or rock is stripped away from land Depositional landforms occur where sediment accumulates after being dropped

© 2007, John Wiley and Sons, Inc. Depositional vs. Erosional Landforms

© 2007, John Wiley and Sons, Inc.Hillslopes Most active zones of fluvial erosion due to high relief creating fast-moving, powerful water Rills Gully