Earth Science
ademola
Sept23_rivers_watersheds.pptxSurface water and the hydrological cycle
PSC 121 Prince George's Community College
The hydrological cycle recycles our water
Surface Water
Two parts
1) Watersheds/Drainage system all the land that
contributes water to the stream
2) Erosion and deposition along streams/rivers
Where does this fit into the hydrologic cycle?
Answer: ground water infiltrates and eventually fills surface water which
flows to oceans
Along the way, we have both erosion and sediment deposition:
Rock cycle and hydrologic cycles interact!
All the land is part of
this watershed
Part 1: Watersheds (or drainage basin) and Tributaries
Its all the land area where water can flow into a stream. Its not just the stream!!
streams
A map of streams in an area
N
Main Stream
tributary to the main stream
tributary to the main stream
Major streams in watershed
Mouth
Lowest elevation
Headwaters
Highest elevation
main channel
Watershed boundary
Tributary to major stream
mouth
headwaters
N
Drainage divide
high spot or ridge
Major stream in watershed
What is general streamflow direction? DOWNHILL!! Any water flowing north?
N
N
Teachers’ Creek
N
If the stream is Teachers’ Creek, the
watershed is called the Teachers’ Creek
watershed or drainage basin.
Teachers’ Creek watershed
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Drainage basin vs. drainage network
Drainage basin is all the land which contributes to streams
Drainage network is the actual streams
Can look at 22.4 and 22.5 in text- not exact match to this material
Area of collection of precipitation
(rain/snow fall)
N
Watershed
subwatershed
Even smaller subwatershed
“sub-sub-watershed”
N
airshed
Nested
watersheds
Watershed is like a funnel
watershed
Container such as Chesapeake Bay
Why should the public care about watershed analysis?
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Pollution control! Track pollution so we can prevent the Bay from getting more polluted
From the Chesapeake Bay Foundation home page (www.cbf.org)
In North America: Major drainages and Divides
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Where does most of the water in the US end up?
Whats the purple watershed?
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The Mississippi River Watershed!
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Know the two continental divides (Rockies and Appalachians) and roughly where they
are on map. What drainages to these Divides divide (answer shown here
is for Appalachians)
Drainage Divide
Runoff to the east
Runoff to the west
Looking north up ridge
To Mississippi or
Great lakes
Atlantic Ocean
For us: its all about the Bay
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Sub-watersheds of the Chesapeake Bay watershed: What 6 river drainages are shown?
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1
2
3
4
5
6
Answers
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Susequehana River- biggest subwatershed of the Bay
What does that mean?
Potomac River
Patuxent River- smallest for the Bay, important for PG
Rappahanock River
York River
James River
Which river is this?
James
York
Rapahannock
Potomac
Patuxent
Susquehana
Where is the mouth of the Potomac?
M
Where might the headwaters of the
Patuxent be?
Maybe up near Frederick ? ---------
Sources (headwater) and Mouth of the Patuxent River
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H
H
Mouth
Patuxent River
Watershed
Potomac River
Watershed
Drainage Divide in
Prince George’s County
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How does PGCC connect to the Bay- Follow the Water!
Google Earth or Maps (I’ve preferred Maps)
Small stream on corner of campus – down hill from the rest of campus
Feeds the SW Branch of the Western Branch of the Patuxent
Next is the Western Branch
Next is the Patuxent, right near Jug Bay and from there to the
Ch. Bay
Erosion and Deposition -1
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Headwaters. Near the drainage divide,
the source of a stream or creek.
Often steep mountain valleys:
erosion is high here: little or no deposition
Cross section of a Mnt. Stream Valley
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Rapid flow cuts a deep channel: Makes a V-shape
Headwaters of a stream or river
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Erosion and Deposition - 2
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1. Steep mountain valleys:
erosion is high here
2. Downstream out of the mountains
Floodplains: (less steep)
some erosion but deposition
is higher here rivers/streams
will meander
Floodplain and meandering stream– flat bed valley
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Why is this the best farmland and why can it be dangerous?
Rhine River in Europe
How many meandering rivers in the Potomac River Watershed?
Erosion and deposition together
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Erosion on the right side of the photos
Sediment deposition (beaches) on the left side of the photos
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Sligo Creek in Silver Spring MD: Beach and RipRap
Riprap: large rocks installed to prevent erosion. Usually on
opposite side of stream from a beach
Beach
Beach
Deltas: end of line for a river
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land built up by deposits of sand and silt at the mouth of some rivers
Large particles deposited first (why?), smaller further off shore
As new sediment comes downstream- it “makes land”
“fingering”: little channels getting clogged
Two classic Deltas where are they?
Erosion and Deposition- 3
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1. Steep mountain valleys:
erosion is high here
little deposition
2. Floodplains: (less steep)
some erosion but deposition is higher here rivers/streams will meander
3. Deltas or the mouth of the river: Flat, the end of the line
no erosion
everything is deposited
Edges of oceans- if not at a delta
Continental shelf is really the extension of the continent.
Sediment build up (probably when sea level was lower) – river deposition
Exposed when sea level lowered
Legally, often considered part of adjacent country
Mississippi Delta and continental shelf in Gulf of Mexico
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Shelves and Plates
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Which way is this plate moving?
Converging
Practical application of continental shelves…. Oil rigs or….
Off shore wind farms can be built in shallow water but far away from
land so you don’t see them from the beach. The above is near
Rhode Island. A wind farm 8 times the size is planned for 17 miles east
of Ocean City to provide 2-3% of MD electricity.
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Location of the wind farm
Landforms: Oceans “Earth without water”
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Can you see the shelves sticking out from the continents?
Summary to know
1. Rivers/streams (v-shaped valley, flood plains, tributaries, headwaters, mouth, delta,
continental shelf, and streamflow)
2. Watersheds, technical terminology: drainage basin, divides, main stream/branch,
tributaries, subwatershed, headwater, mouth
3. Know local watershed: PG County
4. Regional watersheds: what feeds into the Bay
4. National watersheds: Mississippi, Pacific, Atlantic
| V-shaped Valley | Flood plain | Delta or Continental Shelf | |
| EROSION & STREAMFLOW | HIGHEST FASTEST | LOWER SLOWER | VERY LOW ZERO |
| DEPOSITION | VERY LOW | HIGHER | HIGHEST |
