Chapter 16: The Fluvial ProcessesI. The Impact of Fluvial Processes on the EnvironmentA. external land-shaping agents that work by erosion and deposition:1. running water a. most important external agentb. contributes more to shaping landforms than all other external agents combinedc. occurs everywhere except Antarctica2. wind3. coastal waters4. subsurface waters5. moving iceB. fluvial processes: processes that involve running water1. overland flow: unchanneled downslope movement of surface water2. streamflow: channeled movement of water along a valley bottomC. landscape-sculpting effects of fluvial processes:1. smooth irregularities:a. wear down hills by erosionb. fill up valleys by deposition2. often create deep canyons and steep slopes as preliminary stageII. Some Fundamental ConceptsA. Valleys and Interfluves1. all continental surfaces consist of these 2 topographic elements2. valley: that portion of the terrain in which a drainage system is clearlyestablisheda. includes valley bottom and valley sides3. interfluve: higher land above the valley sides that separate adjacent valleysa. ridgetops, mountain crest, or broad, flattish divides between drainage systemsB. Drainage Basins1. drainage basin/watershed: all the area that contributes overland flow and groundwater to a particular stream2. drainage divide: line of separation between runoff that descends in the direction of one drainage basin and runoff that flows toward an adjacent basin3. the drainage basin of a principal river encompasses the smaller drainage basins of all its tributariesIII. Stream SystemsA. Stream Orders1. stream order: concept that describes the hierarchy of a drainage neta. small streams come together to form successively larger onesb. first-order stream: a stream without tributariesc. second-order stream: formed from confluence of 2 first-order streamsChapter 16: The Fluvial Processes – p. 1 of 10d. third order stream: formed from confluence of 2 second-order streamse. joining of a lower order stream with a higher order stream does not increase the order below the confluence: i.e. the confluence ofa first-order and second-order stream does not produce a third-order stream2. in a well-developed drainage system, one can expect the following:a. first-order streams and valleys are more numerous than all others combinedb. first-order streams are the shortest; average stream length increases regularly with increasing orderc. first-order streams have the smallest drainage areas; average watershed area increases regularly with increasing orderd. average stream gradient decreases with increasing orderB. Erosion and Deposition1. introa. all external forces remove fragments of bedrock, regolith, and soil from their original positions (erosion), transport them to another location, and set them down (deposition)b. landforms of erosion differ from landforms of deposition2. Erosion by Overland Flowa. splash erosion: erosion caused by the collision of raindrops with the groundb. sheet erosion: erosion caused by water moving downslope as a thin sheet, transporting material loosed by splash erosionc. rill erosion: erosion caused by the break up of the sheet flow into multitudinous tiny parallel channels, called rillsd. gully erosion: caused as rills coalesce into fewer and larger channels3. Erosion by Streamflowa. once surface flow is channeled, its ability to erode is greatly increased by the increased volume of waterb. mechanisms for stream erosion:1) hydraulic action: direct power of moving water; can excavate and transport material at the bottom and sides of the stream2) abrasion: chipping and grinding effect of rock fragments as they are swirled or bounced or rolled downstream by moving water3) chemical actionc. variables in the erosive effectiveness of streamflow:1) speed of the flowa) steeper the gradient (slope angle of the streambed), faster the flowb) greater the water volume, faster the flow2) turbulence of the flowa) faster the stream flow, greater the turbulenceChapter 16: The Fluvial Processes – p. 2 of 10b) more irregular the channel surface (channel roughness), greater the turbulence3) resistance of the bedrock4. Transportationa. stream load: solid material carried by a stream1) stream load is sorted 2) finer, lighter material moves more rapidly than coarser, heavier materialb. 3 categories of stream load:1) dissolved load: material, mainly salts, that are dissolved in water and carried in solution2) suspended load: very fine particles of clay and silt that are carried in suspensiona) very slow settling speeds, even in still waterb) fine clay may require 1 year to sink 100 feet3) bedload: sand, gravel, and larger rock fragments moving in a stream by saltation and tractiona) saltation: small particles are moved along in a series of jumps or bounces (applies to water and wind)b) traction: rolling or sliding along the streambed4) generally, most material in a stream is transported by suspended load, least by bedload c. competence: measure of the particle size a stream can transport1) expressed by the diameter of the largest particles it can move2) depends mainly on flow speed3) size of largest particle can move varies with the sixth power of the water speed  even small streams can transport very large boulders when in flood stage d. capacity: measure of the amount of solid material a stream has the potential to transport1) expressed as volume of material passing a given point in the stream channel during a given time interval2) can vary tremendously over time depending on:a) flow volumeb) flow speedc) load characteristics3) stream capacity is greatly expanded during flooding 5. Depositiona. erosion is inevitably followed by depositionb. ultimate destination: ocean, lake, or interior drainage basinc. deposition occurs as either flow speed or water volume decreases1) locations of stream deposits:a) mouths of canyonsb) on floodplainsc) at riverbendsChapter 16: The Fluvial Processes – p. 3 of 102) most waterborne debris is deposited by moving water (stream or river) into quiet water (ocean or lake)d. alluvium: any stream-deposited debris1) alluvium is sorted by size – smaller particles are carried farther by running water than are larger particles2) alluvial material is typically smoothed and rounded C. Time and the River1. uniformitarianism accounts for tiny streams in extensive valleys:a. extraordinary length of geologic timeb. the epic work of streams is primarily accomplished by flood flows 1)