Exam 2

What are the general characterisitics of headwaters?

Highest slopes, fastest current, highest sediment erosion rates as it moves downhill and accumulates surface and groundwater. Starting point is mountain spring, lake, wetland, etc.

What is the thread of a channel?

How many channels are in the main channel (single or multiple)

What is a type 1 hydrograph?

-Baseflow controls the response -High infiltration and/or low rainfall intensity

What is manning's n dependent on?

-Bed material -surface irregularities -variation in the shape and size of the channel cross section -vegetation/obstruction -meandering

What is a type 3 hydrograph?

-Both baseflow and overland flow control the response -Combo of type 1 and 2

Describe a steep catchment.

-Few depressions -Thin soils -High water velocity

Compare and contrast a floodplain and a wetland.

-Floodplains are areas of land adjacent to a stream that experiences periodic flooding. -Wetlands occur along coasts, low-lying areas, and floodplains. -Both act as a transitional area between water and upland areas and provide ecosystem services.

Describe open channel flow.

-Flow in streams, ditches, channels, rills, gullies, etc. -The surface of the slow is open to the atmosphere as opposed to a pipe or groundwater flow.

Describe weathering.

-Forms soils which can vary across watershed -Provide dissolved particulate material. -This process is physical, chemical, and biological

Describe the isotopic composition of precipitation.

-Heavier elements prefer to condense while lighter ones prefer to evaporation. -There is a removal of heavy isotopes by condensation as air masses migrate to the poles. -Evaporation of water at higher latitudes occurs at lower temperatures so we'll see a higher concentration of ligher isostopes in the atmosphere.

What is the purpose of Reynold's Number?

-Helps predict flow patterns in different fluid flow situations. -It's the ration of interial forces to viscous forces (i.e., how fast the fluid is moving relative to how viscous it is.). -Re=vR(density of fluid/molecular viscosity) -True laminar flow: Re<500 (viscous forces dominate, smooth and constant fluid motion). -Well-defined turbulence: Re> 2,000 (inertial forces dominate, chaotic and unstable conditions).

Describe how topography affects a watershed.

-It defines the watershed boundaries -Affects the flow velocity -Affects what vegetation is present.

Describe the energy balance in an ecosystem.

-It's how much energy is provided to a basin ecosystem. -Ultimate source is sunlight which can vary by latitude. -Energy inputs to water, plants, animals, etc.

What is the hydraulic radius?

-It's the measure of flow efficiency. -R=A/P(wetted perimeter) -Flow speed depends on friction -Large R=higher channel efficiency

Describe erosion.

-Movement of sediments (weathered material) to/in streams. -Assessment of material carried into streams include turbidity, TSS, and Suspended Sediment Concentration (SSC).

What is a type 0 hydrograph?

-No response -Dry soils and/or low rainfall intensity. -All rainfall absorbed

What wetland ecosystem services are offered by wetlands?

-Nutrient cycling -Maintain water quality -Attenuate floodwaters -Replenish groundwater -Reduce erosion -Provide recreation, aesthetic value, and education

Where would turbulent flow occur?

-Occurs at meander bends -Rapid changes in gradient -Around obstructions -Can cause flow up stream in some locations.

What is a weir?

-Overflow dam used to alter the flow characteristics of a stream. -Used to make streams navigable, control flooding, or measure discharge. -They have a known cross sectional area.

What is a type 2 hydrograph?

-Overland flow controls response -Low infiltration and/or high rainfall intensity.

Describe laminar flow.

-Particles of the water move in straight paths. -No disruption of neighboring particles. -Resistance from intermolecular viscosity. -Resistance is proportional to velocity.

What does the shape of the watershed determine?

-Path length for water -Storm path -Differences in slope angles/direction (rain amount, ET rates).

Describe temperature-dependent stable isotope fractionation.

-Temp differences cause fractionation -Differences in vibrational energies are most pronounced at low temperatures. -At higher temperatures, greater vibrational energy for both heavy and light isotopes. These differences become smaller and produce less fractionation.

Describe turbulent flow.

-Water moves in multiple directions. -Interaction between flow zones; shear stress transmitted -Inertial forces dominate -Eddy viscosity -Turbulence generated at channel boundaries -Resistance proportional to square of velocity.

What does the size of the watershed determine?

-Water volume -The response (Larger the watershed, the slower the response). -The runoff efficiency increases with decreasing size of the catchment. -Larger catchment= longer travel time.

How to calculate flood recurrence?

1. Gather list of peak annual discharges. 2. Sort from 1 to m where m=magnitude rank and n=years of record. 3. Use T= (n+1)/m 4. Plot 5. Probability in a given year: 1/T

What is the effect of implementing impervious surface such as urban development?

1. Increased sediment load with construction 2. Reduced sediment load following construction 3. Increased magnitude of discharge, effective discharge in particular 4. Increased frequency of higher discharge

How do streams adjust to change?

1. Stream channel starts in quasi-equilibrium (constantly shifting equilibrium). 2. A disturbance occurs. 3. The channel deepens, causing bank instability that leads to bank failure. 4. The stream channel widens due to that bank failure. 5. The flatter and wider stream channel is now unable to transport the increased sediment load and deposition occurs. 6. A new quasi-equilibrium is achieved.

What is an oxbow lake?

A cutoff meander that forms a lake.

What is a natural levee?

A high ridge formed from deposits left by floods.

What is a chute?

A relatively straight part of the channel where a meander is cutoff.

What is the reach of a channel?

A segment of the stream

Describe basin memory in stream evolution.

A stream channel adjusts to perturbations (flood, landuse change, etc.). Here we will see channel margins erode and gravel/sand bars move. The stream takes time to re-equilibriate to the average discharge.

Define stream stability.

A stream not undergoing rapid changes.

What is a backswamp?

A type of wetland that is left behind when flood waters recede.

What is a terrace?

An old floodplain that is higher than the main floodplain and rarely sees floods.

What is a flume?

Artificial water channel/chute

Define ecosystem services.

Benefits to humans from the natural environment.

What are the general characteristics of the depositional (mouth) zone?

Empties out into another water body, we see the lowest slope, slowest current, widest bank to bank area, and highest sediment deposition rates. This is where we see large volumes of slow moving water.

The hydrograph separation line that separates old baseflow water from new stormsurge water is always correct, true or false?

False

Define backwater flooding.

Flooding upstream due to conditions happening downstream such as high flow and channel restriction.

What is the significance of flow in a stream?

Flow conditions rremove, transport, or deposit dissolved species and sediments. Flooding increases the interactions between the land and the stream.

What is a splay?

Formed when a levee breaks, releasing flood water behind it.

What is hydraulic jump?

Forms when a liquid at high velocity discharges into a zone of lower velocity. It's the abrupt rise over the liquid's surface. Can also occur when rapid flow encounters a submerged obstruction if it is large enough.

Where do sediments tend to settle?

In places where water velocity is low or where settling depth is small.

What are isotopes and how are they helpful in hydrology?

Isotopes are atoms with the same number of protons but a different number of neutrons. They can be used to trace the natural processes and determining the ages of different materials. Ex. carbon dating or tracking water through the water cycle knowing that heavier elements (higher isotopic number) will precipitate first but evaporate last.

How does changes in landuse/landcover affect a stream system.

It can affect stream flow. For example, if we increased construction, farming, and urban development, we would see an increase in impervious surfaces. So in a storm event, we would see a much higher spike in discharge because surface water can not infiltrate into the ground.

What is Rayleigh fractionation?

It describes fractionation that takes place in unidirectional reactions. -With evaporation and condensation, the reservoir is constantly becoming smaller. -Rates of both are faster than the equilibrium process.

What is a 100 year flood?

It is not a flood that happens every year. Instead, it is more of a 100-year recurrence interval in that there is a 1 in 100 chance the flood will happen in a given year.

What is the problem with levees being built too high?

It makes it so that there is less space for flood water to flow and so water level rises higher and greater amounts of water are forced downstreaming putting more stress on downstream levees.

What is the purpose of Froude Number?

It's the ratio of intertial and gravitational forces used to describe different flow regimes. -F=v/(dg)^(1/2) -F<1= Subcritical flow, where the channel is not steep (tranquil, lower flow regime) -F=1= critical flow -F>1= supercritical flow, where the channel is steep (rapid, upper flow regime. Inertial force is more influential than gravity. Flow velocity is higher than wave velocity).

What is isotope fractionation?

It's the separation of light and heavy isotopes generally due to mass differences causing different vibrational energies in the light and heavy isotopes. -Mass-dependent fractionation can allow us to look at measurable differences in mass and the difference in covalent bond strength as heavier elements vibrate less and therefore have stronger bonds.

What is a floodplain?

Land near a stream that is prone to flooding. -Artifical levees and channel modifications are used here to protect humans from flooding.

Describe drainage networks across space and time.

Largest area would be the watershed with the longest recovery time but the lowest sensitivity. As we move to smaller areas such as from a watershed to a floodplain, to a reach, to a habitat, and then to a microhabitat, recovery time will decrease but sensitivity will increase.

Describe a meandering channel.

Less steep, lower sediment supply, less variable discharge, less erodible banks

What is the difference between low flow and floods?

Low flow hydrologic conditions slowly modify the river channel and can determine what aquatic species can live in a river. Floods quickly shape the river channel through sediment erosion, transport, and deposition. They connect river and floodplain ecosystems and provide nutrient-rich sediment to adjacent areas.

Why are traditional stable isotopes used more in hydrology than non-traditional stable isotopes?

Non-traditional stable isotopes are heavier or more difficult to measure stable isotopes used in environmental applications.

How would you calculate the delta notation of O18?

O18= [(O18/O16 Sample)/(O18/O16 Standard)]*1,000 Remember, positive value means enriched and negative value means depleted.

What is a yazoo system?

Parallel tributary stream in floodplain that act as natural levees.

What are the point bars and cut banks in a channel?

Point bars are depositional features on the insides of bends while cut banks (scarps) are erosional features on the outside of bends.

How to calculate discharge of a weir?

Q(m3/s)= 1.84 (L-H/5)H^3/2 (Metric where L and H are in m) Q(m3/s)= 3.333 (L-H/5)H^3/2 (Metric where L and H are in ft)

How do you calculate discharge (Q)?

Q=velocity(v)*cross sectional area (A) A=width(w)*depth(d)

With stream system scales, what is the region, landscape, and watershed?

Region-A board, geographical area with similar macroclimate (ex. African Savannah) Landscape- Is smaller than a region and includes areas with patterns of similar component features (ex. Forest, city, etc.). Watershed-Varies in size; controlled by landscape variations. -Provides water, chemicals, and sediments to streams. -Relief and gravity move materials into channels.

How do you calculate stream slope?

S=h*L L=Length h= Change in elevation along a reach

What is anabranching?

Sections of a stream that are diverted from the main channel and rejoin downstream. Anastomosing is the most common type. -Low gradient -Defined by high organic matter content in sediments -Cohesive banks and large, vegetated, stable islands.

Describe sedimentary, igneous, and metamorphic rock.

Sedimentary- Soft, bedding planes. Igneous- Hard, joints Metamorphic- Range

How does channel shape and size affect flow?

Shallow and wide=slow narrow and deep=fast wide and deep=fastest

Describe an anastomosing channel.

Shallowest slopes, low sediment supply, low variability in discharge, low bank erodibility.

Describe the short term and longterm benefits for using a hydrograph.

Short term: -Looking at flood response -Daily changes in volume Long Term: -Seasonal and annual changes -Past trends -Future trends (climate change/land use) -Impacts on aquatic ecology

What are the general characteristics of transitional zone?

Slope begins to decrease and the valley widens. Stream begins to meander, and we see moderate slopes and current, and highest sediment transport rates.

How are meanders developed?

The meander wavelength is related to width, radius of curvature, and discharge. Occurs with localized outside bank erosion, alternating bars dominant and outgrowth of the thalweg in straight channels (sinuosity>_1).

Describe a braided channel.

Steep slopes, large sediment supply, rapid variations in discharge, erodible banks. -The channel has sm sediment that the stream must find ways around it. -These channels form bars (transiemt, unvegetated, submerged) and islands (more permanent, vegetated, above surface).

How are point bars formed in streams?

Stream velocity is slower in the inner bend of the meander and sediments are deposited.

Describe the upland transition zone.

The area leading into the uplands. This habitat has variable topography and is more influenced by the stream than areas further away from it.

What is the sinuosity of a channel?

The curvature of the channel, valley slope divided by stream channel bed slope. -High sinuosity=lots of bends -Fromed from thalweg and increases with stream order

What is a pool?

The deep portions of streams that are formed as the thalweg meanders to the outside banks.

What is a thalweg?

The deepest portion of the channel generally showing the highest velocity in the channel.

What is the lag time on a hydrograph?

The delay between peak rainfall and peak discharge

Describe steady uniform flow.

The flow is the same in magnitude and direction at every point in the flow system and does not change with time. This normally occurs along short distances in natural channels.

Describe the flow conditions between headwaters (upstream) and mouth (downstream).

The headwaters usually have faster flow and higher erosion, but lower volume. The mouth usually has slower flow and lower erosion, but a higher volume of water.

What is a meander scroll?

The lateral migration of a meander over time.

What is a riffle?

The shallow portion of streams that are formed as the thalweg crosses from one bank to the other.

What is geomorphology?

The study of Earth's surface and surface proccesses. Looks at how land surface is affected by topography, plate tectonics, type of material, wind and water action (weather, erosion), human activities, etc.

What are isotopologues?

These are molecules that differ only in their isotopic composition. Ex. between these molecules the formula is the same such as H2O. However the H might be a protium, deuterium, or tritium.

In stream evolution, when do things change?

They change with dominant discharge in the form of bankfull discharge and effective discharge. -Bankfull discharge assume that the stream channels adjust to a flow that fills the available cross-section. -Effective discharge is the discharge that, on average, transports the largest fraction of the long-term sediment yield(0.8-1.6x bankfull discharge).

Describe the recovery time with basin memory.

This is the healing interval and is typically shorter in humid environments and longer in more arid climates.

What is parent material?

Unweathered rocks and consist of sedimentary, igneous, and metamorphic rock.

What do the variables in Manning's Equation mean? V=(k/n)R^(2/3)S^(1/2)

V=velocity k=conversion factor (1.5 ft^1/3 or 1 m^1/3) n=manning's n (s/m^1/3) which is empirically derived R=hydraulic radius s=slope

What is the riparian buffer?

Vegetated land on the stream edge with unique biology (wetland for example).

Describe how a thalweg is like a rollercoaster.

Water moving through a thalweg speeds up through riffles and slows down in pools. Move from side to side with the meandering bends moving faster on the outer bank and slower turning on the inner bank. Remember the flow towards the bottom is slower because of the courseness of the streambed.

What trend do we see with isotopic variability with distance from the surface.

We tend to see a decrease in variability in the isotopic compostion with distance from the surface through the subsurface.