Hydrology

Geography
Watershed
A topographic region from which a stream or water body receives runoff. Can be described on any scale of size! Nested..?
Drainage Divide or Catchment Area
Dividing lines (ridges) that control into which basin runoff drains (ex: the continental divide).
Global Drainage Divide/Basin
A large scale drainage divide (continental divide divides Pacific from Atlantic).
Internal Drainage
No outlet to the ocean, usually ends in a lake (Great Salt Lake). High water level fluctuations occur in theses, along with evaporation, resulting in high salinity.
External Drainage
Runoff that eventually makes it to an ocean instead of a lake
Rivers
.003% of freshwater- water that’s flowing in a channel. They derive water from surface flow and groundflow
Main Stream
The main channel of a river, the largest
Tributary Stream
Any river or stream going into a main stream
Confluence
Connection between two rivers (main streams)
River System
A network of tributaries. Large rivers- multiple river systems (Mississippi).
River Discharge
Volume of water in a river flow (Q)
Know your damn rivers!
Amazon- largest by discharge! Nile- longest. Lake Baikal- the biggest (also that’s a lake not a river)
River Processes
Rivers carry water and sediment (solid and dissolved).
Fluvial
Stream related processes of erosion, transport and deposition (dumping sediment off).
Alluvium
Material deposited by running water (deposition)
Insolation
Incoming solar radiation, evaporates water
Gravity
That stuff, that like…. makes stuff not fly into space. It makes water flow downhill… WHAT
Perennial
A river that flows year round
Intermittent
Flows seasonally
Ephemeral
Flows after storms
Gaining Stream
Channel bottom lower than groundwater; water moves from ground into channel
Losing Stream
Above the groundwater table; water moves from channel into ground
Stream Order
1st, 2nd and 3rd. When two one’s come together, they create a two. And so on. However, a one coming into a two will not change it. Blah blah.
Drainage Density
Stream length / basin area
High DD
Lots of surface runoff- low infiltration and/or high precipitation
Low DD
Little surface runoff- high infiltration and/or low precipitation
Drainage Patterns
Tell us about bedrock structure, topography and climate (not stream patterns like meandering and braided). This is the BIG picture of a whole system.
Trellis (Drainage Pattern)

One that doesn’t look like the other three (this is the definition I had in my notes…)

 

[image]

Dendritic
[image]Branched out like a tree (like a neuron if you’ve been in psychology)
Rectangular


[image]It’s rectangular like a rectangle, literally.

Radial
[image]Draining outward from center area- like off of a mountain or volcano.
Discharge (Q)
Volume of water flowing past a point on the bank in a unit of time. **Will always be a measurment of length cubed per a unit of time!!! Ex: Q = ft3/sec (cubic feet per second) because Q = velocity x width x depth
Streamflow Measurement Units
Just be able to recognize them, not how they work or what they mean- cubic feet per second; cubic meter per second/ acre-foot per year.
Measuring Discharge
  • Measure the stream width with a tape measure
  • Measure the stream depth with a staff gauge
  • Measure stream velocity with a current meter

Changes in flow change area and velocity. This is a statement. I should make this a question. How often does this happen and what do they use to graph it?
Happens in regular patterns (great definition Nick), and they graph it with a Stage-discharge Rating Curve
Annual Average Q (Don’t need to memorize these, they are just examples)

Amazon- 180,000 m3/sec

Mississippi- 18,200 m3/sec

Cherry Creek- 410 m3/sec

Flowpaths (How precipitation reaches the stream channel)

Overland Flow- the fastest

Groundwater flow

Direct Precipitation

Parts of a Hydrograph
  • Precipitation peak
  • Q peak
  • Rising limb (when Q is rising)
  • Fallling Limb
  • Baseflow

Different Types of Hydrographs
  • Subdued Hydrograph- has a lower peak that occurs later
  • Flashy Hydrograph- high peak that occurs earlier
  • More urbanization increases runoff and decreases infiltration

What affects hydrographs?
  • Wildfire (affects permeability)
  • Sandy soil makes more subdued hydrographs, while clay makes flashier hydrographs.
  • Frozen Soil
  • Deforestation
  • Rainfall Intensity
  • Drainage Density (the number of streams in a watershed)
  • Size and shape of basin (big or small)

Dissolved Load
Find many chemicals in ionic florm (positive or negative)
Suspended Load

Tiny rock particles (clay, silt, fine sand) taht flow aloft with the stream (not dissolved). Held up by turbulence.

  • Lamminar flow- straight line
  • Turbulent flow- circles, rolling churning and swirling

Bed Load
Bigger sized things, such as gravel, pebbles and boulders. Rolled along the bottom. Saltation– bouncing. Imbricated bed load shows flow direction by how the rocks are stacked up.
Hydrologic Action Erosion
Erosion by turbulence of water; pick things up and lift them
Abrasion Erosion
Erosion by frictioin of suspended sediment and water, like sandpaper.
Sediment Load
Bed load + suspended load; the weight of sediment that a stream can carry
Stream Capacity
The total load that a stream can carry. If stream capacity ; than sediment load –> you get the erosion of sediments becuase it can carry more sediment. If stream capacity is
Stream Competence
The size of particle that a stream can move (depends on velocity). Takes a higher velocity to erode clay because it sticks together.
Aggradation
If sediment load it will deposity alluvium
Stream Channel Forms
There are three forms. They depend on the longitudinal profile (how steep it is). The greater the gradient, the more energy there is and the higher the stream competence.
Straight Channel

In the headwaters…

  • Steep gradient
  • Single Channel
  • V-shaped valley
  • Coarse sediment
  • Small floodplain (where the river would spill out if it left the channel)
  • Nick Point- indentation in the land, waterfalls at these

Braided Channel
  • Reduced Gradient
  • Coarse sediments are deposited, keep suspended sediment
  • Broader floodplain
  • Multiple shallow, stream channels

Meandering
  • Near mouth
  • Low gradient
  • Find sediments
  • Form on large, sinuos, single channel
  • Wide, flat floodplain

Stream Channel Parts
  • Erosion on the outside of bends where water is moving the fastest. This is the thalweg, where velocity is at its highest. Deposition on the inside of bends.

Undercut Bank
The bank of the river where there erosion, where the thalweg is
Point Bar
Bank of river where deposition occurs
Oxbow Lakes
[image]Isolated former stream channel; where the stream has been cut off. Will disappear and dry up after a while.
Bluffs
High ground that bounds floodplain
Terrace
NOT A BLUFF, but bounds the current floodplain. Difference is, it is where the floodplain used to be. Farming is often done on these because it has delicious soil.
Points of dams
  • Flood control
  • Water storage
  • Diversion and Irrigation
  • Hydropower

How do dams alter natural river systems?
  • Drown landscapes (like Lake Powell)
  • Traps sediment behind dam and can starve downstream of sediment.
  • Lower stream temperature below the dam which harms fish
  • Increase evaporation
  • Blocks fish migration

How do dams change river hydrology?
  • Change peak of annual flow and discharge
  • Change in timing of annual discharge

Negative effect of dam- the lack of a spring flood allows invasive species to take hold in floodplain of rivers (salt cedar-lined banks of the Colorado River)
No back side (didn’t know how to turn that into a question/flashcard)
Were controlled dam discharge/floods a success?
Yes! Tried in the Grand Canyon from Glen Canyon Dam. removed vegetation from beachs and rebuilt beaches.
Reasons for Dam Removal
  • Aging Structure
  • Increased Costs (monetary and ecological)
  • Changing Needs

Regional Flooding
Very widespread flooding
Flood
High water level that overflows the natural (or artificial) levees (bankfulls) along any portion of the stream
Floodplain
low-lying area along a strea mchannel, created by and subject to recurrent flooding; alluvial deposits
We tend to have baised views of floods as unpredictable, disastrous events. In reality, they are predictable and necessary occurrences.
This one doesn’t work as a flashcard yo
Flood Benefits
  • Alluvial sediments create fertile soils
  • Provide water resources and recharge groundwater
  • Create important habitat for species such as amphibians or migoratory birds

Flood Frequency and Equations (BIG FLASHCARD)

The probability that a flood of a certain magnitude will happen in any give year. R = (N + 1)/m where N equals total number of events and m is rank.

P = (1/R)*100%

 

Therefore, a ten year flood means that there is a 10% chance of a flood of that size happening every year (1/10). Or a 100 year flood means that there is a 1% chance for that flood.

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