Exam 2 Flashcards
- List three common stream zones and describe their characteristics.
a. Headwaters – high potential energy, steep slope, narrow/shallow channel, high bedload, V-shaped valleys
b. Transfer zone – potential and kinetic energy nearly equal, resulting in more stable stream beds, medium slope, wider / deeper channel, suspended sediment
c. Depositional zone – potential energy is the lowest, sediment is deposited
- Diagram using different profiles of a stream the following features: riffles, runs, pools, glides, thalweg,
riffles- shallow w/ steep water surface
runs – deeper w/ less turbulent surface
pools – forms on outside bend, along banks, behind boulders. Water moves slower, deposition
glides – transition from pool to riffle
thalweg – Deepest part of the river. Created by focused erosion from increased velocity
- How does pool-riffle sequences and the meandering of the stream channel influence the energy of the stream? (answered over multiple slides)
a. it helps to dissipate kinetic energy
- How frequent do rivers reach their bankful width and how does this correlate with the flood plain?
a. about every 1-2 years. Once the bankful width is exceeded, the water inundates the flood plain
PFC of riparian floodplains exists when adequate vegetation, landform, or large debris is present to ________.
a. reduce erosion
b. trap sediment
c. build/enlarge the floodplain
- Describe separately using Lane’s Balance what a river will do as a result of sediment amount, water amount, channel slope, and sediment size
Overgrazing, Dewatering, Mud slide into stream
a. Overgrazing in a watershed – increased water and therefore erosion initially, to correct the river would increase in sinuosity decreasing the slope and restoring Lane’s balance
b. Dewatering of a stream from a diversion – Initial loss of water will cause increased deposition, until the steepness of the channel slope increases to correct
c. Mud slide into a stream – initial increase in sediment causes the balance to switch to deposition. Corrects by increasing channel slope by reducing meandoring
The units for stream discharge are 〖ft〗^3⁄sec . Describe how those units are achieved.
- You take a section of the river and multiply width (ft) x height (ft) = ft^2
- multiply ft^2 by velocity (ft/s), and you have cubic feet / second
- You can find the depth and flow of each subsection, and fine the average to get a measure of discharge
- Describe seven different ways for measuring stream flow.
- With a current meter – use the method described above
- float method – time the distance it takes for an object to flow a known difference
- dilution gauge – often applied to turbulent streams. Tracer (a salt) added to stream, and a reader detects the change in electro-conductivity
- stream gauge station – measures height of a stream and estimates flow from a rating curve. Height determined by a pressure gauge
- Bucket and stopwatch method – temporarily dam water so it goes through a pipe, place a container of known volume under pipe, using a stopwatch, time how long it takes to fill the container, repeat 3x to obtain an average
- flume – channels all the water through. Using the height and the known dimensions, you can determine stream flow
- Weirs – a weir will backup the water like a dam. Otherwise identical to the flume method
- Contrast the hydrographs of a snow-dominated system compared to a rain-dominated system.
- Snow dominated has a rising limb in April/May
- rain dominated has several peaks that may be continuous over more of the year
- What is the difference between a perennial, intermittent, and ephemeral stream? As part of your answer define their relationship with ground water.
perennial – maintains flow during dry and wet seasons, flows at least most of the year. Connected with water table
Intermittent – only flows during wet season. Close to water table when table is high
Ephemeral – rarely flows (regardless of season). Almost always above water table
- Write the calculation for stream: entrenchment ratio, sinuosity
c. Entrenchment ratio – Flood prone width / Bankfull width. Ratio of 1.0 means the floodprone width = bankful width
f. Sinuosity – channel length / valley length. A ratio that tells us how curvy a river is
- What is the Wolman Pebble Count used for?
- Helps you determine the main substrate material in your stream
Briefly describe after reading the notes section in the presentation what an Aa+, A, B, C, D, DA, E, F, and G streams are.
Aa+ - Occurs on very steep gradients. Naturally entrenched. Narrow and deep with little meandering.
A – Occurs on 4-10% slopes. Multiple step/pools. Low sediment storage capacity, high sediment transport capacity.
B – Occur on moderately steep to gently sloped terrain. Moderately entrenched. Wider and shallower than A type. Rapids dominated bed morphology
C – Slightly entrenched with well developed floodplain. Relatively sinuous with a channel slope of 2% or less. Point bars are common.
D – Multi-channel stream where stream channels are highly unstable and shift frequently. Very wide and shallow.
DA – Multi-channel stream where stream channels are relatively stable, stabilized by vegetation. Extremely gentle channel slopes, commonly at or less than .0001
E – Highest sinuosity. Developmental “end-poiint” of channel stability. Often develops from the “F” stream types. Narrow and deep (low width/depth ratio).
F – Entrenched and meandering, working towards re-establishment of a functional floodplain within the confines of a channel that is consistently increasing its width within the valley. High width/depth ratio.
G – G or „Gully“ stream type. Entrenched, narrow and deep step/pool channel with a moderate to low sinuosity. High bank erosion rates and high sediment supply.
- What does PFC stand for
Proper Functioning Condition
- Define these terms – riparian, wetland, lentic, lotic
a. Riparian – an area of land directly influenced by permanent water. Visible in vegetative and physical characteristics reflective of permanent water influence.
b. Wetland – Areas with “hydric” soils that are permanently or seasonally saturated by water
c. Lentic – aquatic system with standing water
d. Lotic – aquatic system with moving water
