ESS 474 - UTK exam 1

The environmental questions you are likely to be addressing usually fall into one of what two categories?

• current status

• likely impacts of alternative management

Conceptual Models and Information

How does a small paper ball dropping through the air differ from a similar piece of paper dropping as a flat sheet?

- sheet has large-scale turbulent eddies

Under what conditions of driving force and chaotic resistance can we accurately predict a natural phenomenon?

- large driving force relative to scale of chaotic resistance

Besides the paper dropping through the air, give an example of a diffuse driving force and large-scale chaotic turbulence

- weather patterns

If I drop a sheet of dense metal (e.g., lead) rather than paper, will the fall time be more or less predictable, and why?

- more predictable

- larger driving force relative to the scale of turbulence

How are replicates defined, and what purpose do they serve?

- assumed to be the same

- show inherent variability

Hydrologic Cycle

List the elements of the hydrologic cycle.  Do not include the driving forces

- ET

- ppt

- infil

- runoff

- subsurface

            - unsat

            - sat

- interflow

- baseflow

- streamflow

Via what path does most of the rainfall onto the land surface take in actually entering the ocean?

- surface flow; very little as subsurface direct

List the driving forces for the hydrologic cycle.

- sun

- gravity

- earth’s rotation

- earth’s residual heat

- NOT wind // physiochemical

Which hydrologic cycle element acts as a valve, essentially controlling how fast the water moves?

- infiltration

Give an example of why it is important to think of the hydrologic cycle over the 3-D landscape, and not just at a point.

- runoff at one spot infiltrates at another

About what percentage of the earth’s fresh water is in the atmosphere at any time?

- 0.04%

What percentage of the earth’s precipitation falls on land?

- 10%

About what portion of the rain falling on lush vegetated land ends up as evapotranspiration?

- ½

Explain why a small hydraulic radius means that you will have a slower flow in your channel

- more water in contact with the rough surface

Input energy and ET

Describe (no need for values) what is meant by the “solar constant”.

- fairly constant solar radiation at the edge of the atmosphere

Why do we get more solar radiation in Knoxville in June than hits the Equator?

- long days

About what portion of the incoming sunlight actually makes it to the earth’s surface?

- 47%

The area north of the Arctic Circle gets far more hours of sunlight (24 hours) during June than we get in Knoxville.  Why does that area actually get less total solar radiation?

- angle of the sunlight

What are the two main causes of general wind patterns?

- earth’s rotation

- uneven heating

Describe the general diurnal wind pattern (high- and low-velocity times) for inland areas

- lowest at daybreak

- highest in late afternoon

Describe the general diurnal wind pattern (direction of wind) for near-shore areas

- sea breeze during day

- land breeze at night

What is albedo?

- the portion of light reflected back from a surface

Number these from highest (1) to lowest (4) in terms of how much solar energy that reaches the earth’s surface actually goes into each.

___  Stored in plants through photosynthesis     

___  Heating the air (sensible heat)

___  Evaporating water (latent heat)      

___  Radiated back to space as longwave radiation (heat)

- 4, 3, 1, 2                                 2

Using either words or equations, define how relative humidity and vapor pressure deficit are related.

- RH = (e_a/e_s) * 100%; VPD = e_s - e_a

If I heat a closed container (so that no air or water molecules can get in or out) containing moist air but no free water, what happens to the relative humidity of the air in the container, and why?

- down

- ea is same, but es goes up

What is the main factor that controls the saturation vapor pressure?

- air temperature

Wind increases evapotranspiration.  How?

- removes wet air from near the water surface

How does evaporation from snow compare to that from free water at the same temperature?

- much lower

Describe how evaporation from a wet soil changes over time

- when saturated, very similar to free water

- as dries, drops off quickly

Name the two places that water goes as part of the photosynthesis process

- hydrogen source to make sugar

- losses due t evaporation from wet surfaces

How do plants regulate water losses?

- stomate guard cells open or close

Once we have a value for the reference ET, what do we do with that to get the actual evapotranspiration for our specific crop (say, tomatoes) on this day?

- multiply times crop coefficient comparing crop to base (pan, grass, etc.)

- adjust for crop stage

- adjust for soil water

What is the most common equation for estimating ET based on climate information.

- Penman method or some variation thereof

In words, what are the inputs required to use the most common equation for estimating ET?

- incoming solar

- radiation to ground

- wind

Plants over their lifetime pump more water than their biomass weight.  How much more?

____     2 times

____     5 times

____     10 times

____     100 times

____     > 100 times

- 4

What does the pyranometer measure?

- hemispherical shortwave radiation

How is the “average daily temperature” historically defined, and give an example of a case where this would not be a very good value.

- avg of max and min

- hot day with sudden cooling late at night

What are the 2 devices most commonly used to electronically measure temperatures?

- thermistor

- thermocouple

What are the critical factors in operation of a device to measure solar radiation?

- keep clean

- calibrate frequently

What are the 3 general use requirements for a device used to measure air temperature?

- shaded

- ventilated

- > 30m from extensive radiation absorber or reflector

What does a psychrometer measure, and how does it work?

- RH

- difference between wet bulb and dry bulb temperatures

I mentioned 3 concerns for cup anemometers.  List 2 of those

- high threshold speed

- run on

- vertical movement

For general meteorology, how far from a 100-ft tall tree should you put your wind speed sensor?

- 4H = 400 ft

Why is it usually specified that an evaporation pan should be placed on a wooden stand?

- get away from ground temperatures

How is a weighing lysimeter used to estimate ET?

- weighs big chunk of soil and included water

How is “wind run” defined?

- total of (vel * time) over day

Precipitation

Give an example of how we know that ET and the corresponding precipitation may occur far from each other

- Caspian Sea, southern Atlantic near Namibia, southern Pacific near Chile, near CA

About how much does air temperature change with every 1000ft increase in elevation?

-   -5.5 degree F

We mentioned 4 ways in which air lifting occurs.  Describe 3 of these.

- cyclonic pressure-controlled

- cyclonic frontal

- convective

- orographic

Why do raindrops rarely exceed 5mm diameter?

- tear themselves apart through wind resistance

How does expected rainfall intensity change with an increase in the area of interest?

- goes down

How does expected rainfall intensity change with an increase in the time period of interest?

- goes down

Define what is meant by a 2-yr 10-hr storm.

- depth of rainfall

- over any 10-hr period

- exceeded only once in 2 years

Which of the following will occur more often?

___ 2-yr 30-minute storm

___ 100-yr 2-hr storm

___ 1-yr 1-minute storm

___ can’t tell, given the information provided

-3

Which of the following will have the highest instantaneous rainfall intensity?

___ 2-yr 30-minute storm

___ 100-yr 2-hr storm

___ 1-yr 1-minute storm

___ can’t tell, given the information provided      

- 4        X

When will I be most interested in each of the following:

a) rainfall intensity

            - chokepoint

b) rainfall depth

            - storage

Describe the 3 parts of a good manual raingage

- sharp clearly-defined collector

- concentrator tube

- storage

For a weighing raingage, what are the

a) advantages?

            - continuous

            - accurate

b) disadvantages

            - need to empty

            - evaporation

For a tipping bucket raingage, what are the

a) advantages?

            - digital

            - accurate

            - relatively continuous

b) disadvantages

            - poor resolution at

            - evaporation

What must you do to ensure the accuracy of Doppler radar estimates of rainfall?

- ground-truth

What is the biggest concern with location of a raingage, and how is it addressed?

- wind effects

- shielding

Explain why raingages should generally not be placed on a sideslope

- wind direction affects reading

Explain why raingages should generally not be placed on rooftops

- turbulence

Do we generally want raingages placed on a pattern or randomly distributed?  Explain why

- pattern

- looking for relatively random effects

If raingages were placed at the density suggested by the Weather Bureau for “general meteorology”, how far apart would the gages be?

- 15 miles or 25 km

I will need more raingages to adequately cover a specific area under what 3 conditions?

- summer storms

- orographic effects

- short-term study

If I have storm rainfall values at several locations nearby, describe the procedure that I use to estimate what the rainfall was here?

- point estimate method

- inverse distance squared weighting

How do I check whether a raingage gives consistent readings over time?

- compare to nearby gages using PEM

If I have storm rainfall values at several locations nearby, how do I get an average rainfall depth over the entire area of interest?

- Thiessen Polygon Method, isohyetal method

What are the general problems experienced with measuring snow?

- getting snow into the gage

- hits ground very unevenly (drifting)

- can be moved again once hits ground, so can be double-counted

Describe use of a manual or weighing raingage for measuring snowfall

- remove funnel

- put known volume of salt solution in bottom

Describe use of a tipping bucket raingage for measuring snowfall

- need heated funnel and body

Describe use of snow pillows for measuring snowfall

- flat bladder filled with antifreeze

- measure pressure

- placement critical

Describe use of a snow survey for measuring snowfall

- lay out transects beforehand

- stay out of poorly-drained areas

- take snow samples for water content

What is the general range of depths of snow equivalent to 1” of water?

- 5-12”

Infiltration

What impact does soil texture/structure have on infiltration?

- pore sizes control ease of movement of water through the soil

What impact does soil subsurface water flow patterns (e.g., impermeable layers) have on infiltration?

- keeps water from getting out of the way

By what specific processes do “good management” help increase infiltration?

- controls surface sealing

- more macropores

- slows runoff

Draw a graph of “normal” infiltration rate over time.

- starting high infil rate

- steady- state infiltration rate

Make a graph, labeling the axes with time on the x-axis and infiltration rate on the y-axis.  Now draw two curves on that graph.  The first (solid line) should represent what happens under classical Hortonian conditions, and the second (dashed line) what happens under non-Hortonian conditions with an impermeable layer some distance under the surface.

- Hortonian show decrease and steady-state

- non-Hortonian show sudden drop

What measured values are used in developing the Horton infiltration equation?

- initial infiltration rate

- steady state infiltration rate

Draw a graph of the actual infiltration rate if the rainfall rate is less than the initial infiltration rate but more than the steady-state infiltration rate.

- straight line over to curve

- follow curve down

Why are lab tests for infiltration rates questionable?

- small scale

- variability

- rainfall

- spatial flow

What is the concern with any ponded infiltration measurement technique?

- unrealistic driving force

Why is a double-ring infiltrometer better than a single-ring?

- vertical flow

Why is a sprinkling infiltrometer better than a double-ring infiltrometer?

- larger area

- water applied like rainfall

- allows for various managements

What are the concerns with using normal contact infiltrometers (e.g., disc or Guelph permeameter)?

- small area

- no management

Subsurface Flow

According to Poiseuille’s Law, if I double the radius of a tube and all other parameters remain the same, by how much do I increase the flow rate?

- 2⁴ = 16 times

What are the problems with modeling water flow in soils as a series of tubes flowing based on Poiseuille’s Law?

- have all sorts of irregularities (tortuosity, dead ends, irregular shapes, interconnectedness)

On what simple engineering concept is Darcy’s Law based?

V = F / R

Write the simple Darcy’s Equation, using v = velocity, K = conductivity, L = column length, and F = driving force

- v = K * F / L

Is the actual flow velocity through the pores (the “seepage velocity”) slower or faster than the Darcy’s velocity, and by what factor?

- faster

- / porosity

How big must the subsurface flow Representative Elemental Volume be?

- large enough so that the presence or absence of any single pore (R⁴) doesn’t matter

What is meant by “preferential flow”?

- most of the water flows through a very small volume of soil

What is meant by “wetting front instability” or “fingering”?

= flow does not advance evenly

What 2 factors control the gravity force driving subsurface flow?

- depth of ponded water above surface

- length of continuous water column subsurface

If the soil is saturated just to the soil surface, how is Darcy’s Law simplified?

- F/L = 1

How does the adhesion force of soil to water changes with thickness of the water layer?

- Fs prop 1/T⁴

How do the adhesion forces between water and soil tend to cause water to move?

- wetter to drier

- vapor transfer can be important

Friction forces of the soil on water flowing through it have what relationship to the velocity of that flow?

- V_s²

What is the controlling force in saturated subsurface flow?

- gravity

In terms of Darcy’s Law, why is unsaturated subsurface flow so complicated?

- both F and K change with water content

Describe the overall flow behavior in the vadose zone

- most movement through relatively small area

- pores may not be flowing full

- dam spillover effect

- “breathing” between pores and matrix

- interaction with uneven infiltration

- importance of lateral movement underestimated

How is groundwater flow usually estimated?

- Darcy’s Law

- wells to define F and K

For what is a flow net used?

- estimate the direction and velocity of subsurface saturated flow

Are most subsurface flow measurements for saturated or unsaturated flow?  Why?

- saturated; so much easier to deal with

What can percolation lysimeters measure?

- vertical macropore flow in vadose zone

What can vacuum lysimeters measure?

- some measure of flow rate at specific suction

What can auger hole and bore hole methods measure?

- horizontal hydraulic conductivity

Tracers can be used with subsurface flow in 2 ways.  Describe those.

- mark path taken by water

- measure flow directly

What does it mean to say that a tracer is “conservative”?

- stays in water

Describe the difference between “rainfall excess” and “saturation excess” runoff.

- rainfall excess cause by P > I

- saturation excess caused by subsurface filling up

Why is it so hard to get a good handle on saturation excess runoff?

- spatial variability

- temporal variability

- temporal-spatial linkage

In what case can we get negative baseflow?

- high stream levels

Describe the “leaky bucket” approach to streamflow disaggregation techniques

- assume qt = q0 * exp(-kt)

Runoff

With relation to the soil, runoff can result from 2 different processes.  What are those?

- rainfall excess runoff

- saturation excess runoff

What is the definition of a “watershed”?

- entire area

- contributing runoff

- point of interest

How do the runoff rate per unit area and runoff volume per unit area generally change as the watershed area increases?

- both go down

What are some cases in which the watershed area may be very hard to define?

- interflow

- baseflow

Draw a typical storm hydrograph, labeling the axes.  On this figure, indicate the 3 things about the storm we are generally most interested in.

- flow rate vs time

- volume, peak runoff rate, time to peak

Why does runoff not begin immediately with the beginning of rainfall?

- surface wetting (interception)

- surface storage (detention)

State the 2 different definitions of the time of concentration

- time for entire watershed to be contributing

- time for most remote area to be contributing

Why does the use of time of concentration make less sense as our watershed of interest gets larger?

- storm less likely to cover entire watershed

In most relationships to estimate time of concentration, the travel time for overland flow and for channel flow are treated separately.  Why?

- overland flow so much slower

What factors are important in the relationship we used to estimate overland flow time?

- length, steepness, roughness

What factors are important in the relationship we used to estimate channel flow time?

- length, steepness

Explain why a design storm duration equal to the time of concentration gives the maximum design runoff rate.

- shorter don’t have entire watershed contributing

- longer has less intense rainfall

I mentioned 6 factors controlling runoff.  Describe 3 of those.

- local infiltration controls

- soil and geology (hydrologic group)

- management

- AMC

- topography; infil, but mostly Tc

- management slowing Tc

- watershed orientation and shape =>Tc

- scale (interaction with storms)

- precipitation characteristics

Describe why a storm that is first light then heavy produces more runoff than the opposite pattern.

- infiltration filled up by light rain

Explain why a 50-year rainfall event may not produce a 50-year runoff event

- lots of other factors, especially AMC and infiltration

A “design storm” is a hypothetical rainfall depth on which we will base our runoff estimation.  What 2 factors are used to determine the design storm depth?

- return period

- storm duration

On what basis is the design storm return period chosen?

- cost of failure

Let’s say that you have 4 rainfall maps to work with: A) 2-yr 1-hr, B) 2-yr 24-hr, C) 50-yr 1 hr, D) 50-yr 24-hr.  Which would you most likely pull information from if, for your small watershed, you were designing:

a) a culvert under a small country road   ____________

b) a culvert under a major highway         ____________ 

c) a livestock pond                                ____________ 

d) a reservoir above a subdivision          ____________ 

- A, C, B, D

The “unit hydrograph” approach assumes that a “chunk” of excess rainfall will exit the watershed with what hydrograph shape?

- triangular

The base time (T_b) of the unit hydrograph depends on what watershed parameter?

- Tc

The method we discussed for estimating runoff volume is called what?

- Direct Runoff or Curve Number method

The runoff volume estimation method we discussed uses what 2 parameters as inputs?

- rainfall depth

- Curve Number

One significant problem of the method we used for estimating runoff volume is that it doesn’t take into account what parameter?

- rainfall intensity

How will we decide on a rainfall duration and return period to use in runoff volume estimation?

- usually use long duration (24 hrs)

- return period depends on cost of failure

The method we discussed for estimating peak runoff rate is called what?

- Rational Method

How will we decide on a rainfall duration and return period to use in peak runoff rate estimation?

- duration = Tc

- return period depends on cost of failure

What 3 parameters serve as inputs to our peak runoff rate estimation method?

- area

- peak rainfall intensity

- runoff coefficient C

Collecting 1 inch of runoff from 100 ft² of pavement would give about how many gallons?

- 62 gallons

What are the 4 strengths of using a flow divisor to measure runoff?

- simple

- reliable

- cheap

- continuous sampling

What are the 3 potential weaknesses of a flow divisor to measure runoff?

- exact split needed

- velocity effects

- scale

What are the location restrictions in using a weir to measure runoff?

- well-behaved channel

- no submergence => importance of downstream

- no debris and sediment

Why is the H-type flume often used to measure runoff?

- accurate over wide range of flows

- insensitive to sediment (within reason)

- insensitive to submergence

Describe the 2 general problems caused by using a constriction device to measure runoff.

- backs up flow so changes flow pattern

- causes sediment deposition

Why can’t we simply solve the constriction device problem by using a less constrictive device?

- lose sensitivity of flow measurement

How does a drop-box inlet help solve the constriction problem?

- ponding of a small area/volume

Flow in Channels

How do we most commonly separate out baseflow from runoff in streamflow?

- groundwater recession or depletion curve => leaky bucket

The general study of how stream channel systems evolve is called what?

- stream morphology

How do stream characteristics generally change if we increase its sediment load?

- shallower, more meandering, wider

How do we get a 3^rd-order stream?

-  join 2 or more 2^nd-order

Why are weirs or flumes generally not used to measure flow in larger streams?

- expensive

- need to calibrate if not ideal

- debris and sediment problems

Under what conditions can a pipe or box culvert be used to theoretically estimate flow rate?

- simple cross section

- symmetrical entrance

- free discharge at outlet

- two of 6 possible flow types

Why can’t we simply use Manning’s equation to get flow rates in a channel?

- too hard to get good measure of n

- if get once, can use within limited range

Describe the velocity-area method of measuring flow rate in a stream

- divide stream cross-section into sub-segments

- get depth and avg velocity readings for each

- add up flow rates in sub-segments

- redo at various depths

What are the potential problems using the velocity-area method of flow measurement?

- assumes no change in channel over time

- at high stage, flow may change during test

- many calibrations at different stages => cost

- danger

- poor readings at low velocities

- backwater problems

What are the concerns associated with using the velocity-area method to get the high-flow readings soon after a storm?

- danger

- rapidly changes

What are the limitations on using float gaging to get stream velocity?

- dead areas