Human Impacts to Rivers Sediment Water Wood Confinement Valley slope Channel morphology Flow obstructions Bank material Riparian vegetation Human Impacts on Rivers dams channelization loss of woody debris riparian forests More than 80 000 dams affect 90 of the nation s 5 8 million km of rivers QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Dams trap a higher proportion of runoff in drier regions U S Dam construction leveled of in 1980s at almost a billion acre feet Timing of Dam construction varied regionally but was fastest between 1940 and 1980 Hoover Dam QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Timber crib dam in Michigan QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Reservoirs often trap 40 to 80 of the sediment carried by large rivers reducing the sediment delivered to coastal environments despite increased soil erosion in upland environments QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Impact of Humans on the Flux of Terrestrial Sediment to the Global Coastal Ocean James P M Syvitski Charles J V r smarty Albert J Kettner Pamela Green Science v 308 p 376 380 Human s increased annual sediment delivery to rivers by 2 3 billion tons from about 6 5 billion tons to almost 9 billion tons QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Human s decreased annual sediment delivery to oceans by 1 4 billion tons from about 6 5 billion tons to about 5 billion tons QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Less sediment reaches the coast in Asia and parts of the Americas due to dam construction QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Humans have simultaneously increased the sediment transport by global rivers through soil erosion by 2 3 0 6 billion metric tons per year yet reduced the flux of sediment reaching the world s coasts by 1 4 0 3 billion metric tons per year because of retention within reservoirs Splash dams Human Impacts on Rivers dams channelization loss of woody debris riparian forests Los Angeles River at Vernon QuickTime and a TIFF Uncompressed decompressor are needed to see this picture QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Los Angeles River at Canoga Ave California QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Missouri QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Connecticut Illinois QuickTime and a TIFF Uncompressed decompressor are needed to see this picture QuickTime and a TIFF Uncompressed decompressor are needed to see this picture Port of Seattle circa 1870 Lower Duwamish River and estuary Lower Duwamish River today Human Impacts on Rivers dams sediment input channelization loss of woody debris riparian forests Extent of global forests Forests have covered about one third of the Earth s land surface during the Holocene But the extent of forest cover has changed substantially Oregon Amazon Cameroon Few of the worlds forests retain frontier conditions Log jams were significant obstacles to navigation and land development in the western U S Army Corps of Engineers aggressively desnagged American Rivers Snags Year Thousands of snags were removed from Puget Sound rivers between 1880 and the mid 20th Century 10000 Rivers Harbors Skagit River All Rivers 8000 6000 4000 2000 0 1880 1900 1920 1940 1960 LWD can control the formation of pools and bars and thereby channel reach morphology For channels we ve surveyed in Alaska and Washington a plane bed morphology occurs only at low LWD loading 20 pool spacing channel widths pool Greater wood loading leads to more pools plane bed pool riffle SE Alaska NW Washington 15 10 5 0 0 0 0 5 1 0 LWD frequency pieces m 1 5 A Log jams trap copious amounts of sediment and aggrade entire reaches of channel 100 m How big does a log have to be in order to influence a river The key member logs that anchor log jams tend to have a diameter half the channel depth and a length half the channel width NISQ Jams Other SNOH STILL Pieces Kilometer Valley jam Position in Channel Network Queets River Washington Log steps Meander jam Bankfull bench Effects of Wood in Rivers 1000 Valley Bottom 100 Years 10 1 In Channel Pools Cover Bank Complexity 1 Reach Channel Switching Islands Sloughs 100 Water Sediment Wood Routing 10 000 Spatial scale meters Environmental History of Puget Sound Rivers Two dominant types of river valleys Pleistocene glacial and Holocene fluvial Pleistocene glacial valleys were incised by meltwater beneath the Puget Lobe glacier Holocene fluvial valleys were incised by rivers into the Puget Lowland after deglaciation Pleistocene glacial valley Snoqualmie River 16 Lidar DEM 1870 Landscape 2606001 14 12 10 8 6 0 1 000 2 000 3 000 Horizontal distance m Snoqualmie river channel 2606021 16 14 12 10 8 0 400 800 1 200 1 600 Horizontal distance m Channel pattern Meandering Habitats Oxbows and large depressional wetlands Cross valley profile Convex Holocene fluvial valley Nisqually River 1999 aerial 2000 field 18 8 16 14 12 10 8 0 400 800 Horizontal distance m main channel 23 11 21 19 17 15 13 0 400 800 Horizontal distance m Channel pattern Anastomosing Habitats Multiple channels floodplain sloughs Cross valley profile Corrugated from channels islands Examples of cross valley topography Pleistocene valleys Holocene valleys Green River in Tukwila Cedar River near Elliott 12 36 27 xs 89 34 8 32 6 30 4 28 10 2 26 0 1 000 2 000 3 000 Horizontal Distance m 0 500 Horizontal distance m regraded areas e g Southcenter Mall River perched above floodplain River at low point of floodplain Comparative river dynamics Avulsion type Floodplain occupation rate Migration avulsion zone Meander cutoff Slow Narrow Channel switching Rapid Wide Metric Prediction Pleistocene Holocene MORPHOLOGY 1 Channel gradient Low High 2 Stable forested islands Few Many surrogate for branching pattern 3 Sinuosity 4 Cross valley topography Meandering Convex Strait Corrugated HABITATS 5 Wetland area High Low 6 Oxbow ponds Many Few Variable High 7 Total length of floodplain sloughs DYNAMICS 8 Dominant avulsion type 9 Channel migration zone Meander cutoff Narrow Slow rate Channel switching Wide Rapid rate Nooksack River Nooksack River Glacial valley Fluvial valley Change to wetland area in four North Sound estuaries deltas Wetland area hectares mid
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