Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the...
-
date post
21-Dec-2015 -
Category
Documents
-
view
219 -
download
0
Transcript of Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the...
![Page 1: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/1.jpg)
Streams and floods
![Page 2: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/2.jpg)
GoalTo understand how surface-water-drainage
systems (streams) work and the patterns and hazards of flooding.
![Page 3: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/3.jpg)
Hydrologic cycleEvaporation—Precipitation—Storage—Infiltration—
Runoff... also subduction and volcanism
![Page 4: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/4.jpg)
StreamsStream: Any surface water flow confined to a channel
—Everything from little creek in arboretum to Mississippi River
![Page 5: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/5.jpg)
Streams1.Flow from ground water—generally very steady,
called base flow
2.Flow from surface runoff
![Page 6: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/6.jpg)
StreamsDrainage basin (watershed): Total area from which
overland flow reaches a stream
Tributary: Smaller stream that feeds a larger stream
Messalonskee Stream is a tributary of Kennebec River: Its drainage basin is part of Kennebec River drainage basin
Amazon Basin
![Page 7: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/7.jpg)
StreamsDrainage divide: Line
that divides one drainage from another—generally topographic high
Drainage divide in Colorado
![Page 8: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/8.jpg)
StreamsGradient: Slope of stream—vertical drop over
horizontal distance• Meters per kilometer or feet per mile
![Page 9: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/9.jpg)
StreamsStream velocity: Speed of the current• Increases with increasing gradient• Increases towards outsides of bends in channel and
towards channel bottom
![Page 10: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/10.jpg)
StreamsStream discharge: Total volume of water that passes
through a stream channel per unit time• Cross-sectional area (ft2 or m2) x average velocity
(ft/s of m/s) = discharge (ft3/s or m3/s)• Little creek in arboretum discharge = 10’s ft3/s;
Mississippi River discharge = 600,000 ft3/s
![Page 11: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/11.jpg)
Streams shaping Earth’s surfaceStreams are very efficient agents of erosion and
sediment transport• Will rapidly cut down to level at which they can no
longer erode their channels, or their base levels
Stream trying to reach its base level
![Page 12: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/12.jpg)
Stream valleysStream erosion typically creates v-shaped valleys• Stream cuts downwards and sides of valley slide or
wash into main channel until slopes are stable
V-shaped valleys in the Klamath Mountains
V-shaped valley in New Zealand
![Page 13: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/13.jpg)
Drainage patternsDendritic drainages: Contain branching tributaries, like
branches of a tree• Form over relatively uniform substrates
![Page 14: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/14.jpg)
Drainage patternsTrellis drainages: Form in areas where rocks of very
different hardness have been folded or faulted• Streams follow less resistant rock in valleys
Trellis drainages in Virginia
![Page 15: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/15.jpg)
Drainage patternsSuperposed drainage: Drainage pattern that cuts
across surrounding topography. Indicates stream has cut down from a flat surface
Superposed drainage in Wyoming
![Page 16: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/16.jpg)
Stream channel patternsFlood plain: Low flat area adjacent to main channel
subject to periodic flooding
Flood plain of the Kanawha River, West Virginia
![Page 17: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/17.jpg)
Stream channel patternsBraided streams: Channels form anastomosing
(converging and diverging) strands separated by mid-channel bars
• Develop where sediment supply exceeds normal ability for stream to transport it
![Page 18: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/18.jpg)
Stream channel patternsMeandering streams: Stream that winds and loops its
way through the flood plain in a random pattern• Develop in response to current-speed differences
around stream bends
Owens R. in California
Tributary of the Amazon R.
![Page 19: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/19.jpg)
Oxbow Lakes
![Page 20: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/20.jpg)
Pattern left by meanders along Owens River, California
![Page 21: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/21.jpg)
Meandering streamsCut banks: form on the outside of meanders where
fast current is actively eroding channel bank
Point bars: form on the inside of meanders where sediment drops out of slow current
![Page 22: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/22.jpg)
Meandering streamsOnce a meander gets too pronounced, it may be cut
off and bypassed to leave an oxbow lake
![Page 23: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/23.jpg)
Meandering streamsIncised meanders: Meanders trapped in place when
stream cuts down rapidly after tectonic uplift
![Page 24: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/24.jpg)
Stream channel patternsWaterfalls and rapids: Form where stream bed locally
more resistant to erosion or where faulting, landslides, or debris from a tributary have interrupted stream gradient
![Page 25: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/25.jpg)
Stream sedimentSediment load: material moved by stream—we call
stream sediment alluvium
![Page 26: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/26.jpg)
Stream sedimentSuspended load: sediment carried along in water
column by turbulence of current
Bed load: Larger particles that bounce and/or roll along the bottom
Yellow River in China is ~50% sediment by volume
![Page 27: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/27.jpg)
How Streams Move Sediment
![Page 28: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/28.jpg)
Stream sediment deposition• Mid-channel bars and point bars• Levees: ridges of relatively coarse sediment
deposited alongside main stream channel
![Page 29: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/29.jpg)
Stream sediment deposition• Alluvial fans: From when stream leaves a narrow
canyon and enters large, flat valley—Gradient decreases, so current slows and drops most of the sediment load
![Page 30: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/30.jpg)
Stream sediment depositionDeltas: Sediment piles formed when stream enters
standing body of water (like the ocean)• Build outward from the coastline
Mississippi delta
![Page 31: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/31.jpg)
Mississippi River DeltaNew Orleans sits on
Mississippi River delta that formed less than 1000 years ago
![Page 32: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/32.jpg)
City is subsiding ~5mm/yr because sediment supply cut off by man-made levees (we’re keeping the floods out)
• Combined with global 1–4mm/yr global sea level rise
Red = below sea level
![Page 33: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/33.jpg)
FloodsFloods occur when local precipitation runoff exceeds
normal capacity of the stream channel
Factors that influence runoff• Topography• Soil and bedrock• Land use
![Page 34: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/34.jpg)
Flood prediction• Based on past record of yearly peak discharges• Extrapolations made from incomplete data sets
generally underestimate flood size and frequency
Peak discharge is plotted against recurrence interval
![Page 35: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/35.jpg)
Flood prediction100-year flood: according to best available data, 1-in-
100 chance it could happen any given year
Like shuffling a deck of cards and trying to draw the ace of spades 1-in-52 chance every time
![Page 36: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/36.jpg)
Flood control—Can’t preventFlood walls and levees: (man-made) keep water in
main channel. Must completely surrounded inhabited area
• Expensive• Must completely encircle area
![Page 37: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/37.jpg)
Flood control—Can’t preventFlood control dams: store water in reservoirs and
release it gradually• Can impound main stream or lots of small tributaries
• Expensive• Flood large areas• Block fish migrations
![Page 38: Streams and floods. Goal To understand how surface-water-drainage systems (streams) work and the patterns and hazards of flooding.](https://reader035.fdocuments.us/reader035/viewer/2022062407/56649d6a5503460f94a48d88/html5/thumbnails/38.jpg)
Flood control—Can’t preventFlood zoning: Most municipalities don’t allow new
construction inside of areas that will be inundated by discharge predicted for a 100-year flood
• Homeowners insurance doesn’t cover flooding• Must purchase separate flood insurance