hydrology

What indicator species is generally used because of their sensitivity to DO?

Trout

What is the general rule on how low water DO should go?

5ppm

What impact does low pH generally have on water quality?

Get metal instability, especially Al.

What is by far the single largest water contaminant in terms of extent impacted?

sediment

We mentioned 5 different impacts of sediment as a water contaminant. List 3 of those.

-       Sedimentation

-       habitat destruction

-       water supply costs

-       machinery costs

-       adsorbed chemicals

What land use is the source of the most sediment mass, and what land use is the source of the highest sediment concentrations?

ag. runoff ; construction sites

What is the biggest measurement problem associated with sediment in water?

hard to measure solid-liquid mixture

What does BOD stand for?

Biochemical oxygen demand

What is the primary impact of BOD as a water contaminant?

drives down DO

List the steps usually used in measuring BOD.

sampling & incubation 5 days

What is the primary impact of nutrients as a water contaminant?

N + P → veg growth

What is the biggest problem with measuring N as a water contaminant?

  nitrate → dissolved → move with baseflow

  multiple forms

  storage in soil matrix

What is the biggest problem with measuring P as a water contaminant?

  most common bound to sediment

  multiple forms

Why are e. coli bacteria commonly used as a pathogen contamination indicator, when many varieties of the bacteria are benign?

 Easy to detect

Presence indicates fecal contamination

What is the most common source of pathogen contamination?

-Sewers, septic systems

-animal waste

-fecal material

Why is BOD considered to have an acute impact?

 Rapidly reduce DO which leads to immediate and harmful effects on aquatic organisms

Why is in-situ monitoring generally considered to be better than sampling?

IN-SITU MEASURES
– better time resolution → continuous
– clear what represents → here + now
– very few things that can measure
      -– no pump work
      -– harsh environment

Under what conditions can we allow full mixing in order to measure the representative impact of contaminant inflow?

Only really works for a fast mountain stream that has good mixing in a reasonable length

Where must I measure contaminant levels in order to determine the impact of a point source on water quality?

Upstream and downstream

What must I do in order to get a representative sample that includes sediment?

Use a depth-integrated samplers

What is meant by “isokinetic” sampling?

Isokinetic sampling refers to a sampling technique in which the velocity of water entering the sampler is equal to the velocity of the surrounding streamflow at the point of collection. 

Name a contaminant that we can often measure moving with baseflow.

Nitrate

Name a contaminant that we can often measure moving with the first flush.

TSS (sediments)

Name a contaminant that we must really measure throughout the hydrograph.

Sediments

1. When I take a sample:

1) what time frame does the sample actually represent?

2) what time frame do we normally use it to represent?

1. Moment of sampling (a few seconds)

2. Wider time frame, Half way to previous until half way to next

Describe flow-proportional sampling.

Technique where samples are collected in proportion to the flow rate of a storm ensuring that higher flows contribute more to the final sample than lower flows.

What must you do in order to user turbidity as a surrogate for suspended sediment?

To use turbidity as a surrogate for suspended sediment concentration (SSC), you must establish a site-specific, empirical relationship between the two. (not sure)

Development usually results in higher flow rates in the stream during storm events. Why?

ET decreases, Tc decreases, large events resulting in flooding

Development usually results in lower flow rates in the stream between storm events.  Why?

– lower low flows
      – less baseflow

We mentioned three negative impacts of development-caused higher stream flow rates during storm events. List two of those.

– large ⇒ flooding
– medium
       – impact on channel (erosion)
       – impact on ecology

We mentioned four negative impacts of development-caused lower streamflow rates between storm events.  List two of those.

– water supply  for people downstream
– recreation
– ecosystems

How is modern LID different from classical stormwater detention?

There is more ‘retention’ primarily for infiltration 

More ‘treatment’ of contaminants

Describe the difference between “detention” and “retention”?

Detention:Reduce peak flow rates and prevent downstream flooding.

Retention: Promote infiltration, and water quality treatment.

What is the normal “treatment” goal for LID?

treatment ⇒ remove 80% TSS

(TSS = total suspended solids)

Why do some consider rainwater harvesting and reuse to not meet the normal LID goal of a more natural hydrology?

Reduced infiltration compared to natural systems

  If we divide our infiltration area by two, can we get the same overall infiltration results by multiplying our infiltration time by two? If not, why not?

No, this is because with time, the infiltration rate decreases so longer duration doesn’t mean twice the volume.

Relationship between infiltration and time is not a linear relationship.

What is the normal limit on maximum infiltration time for stormwater SCMs, and why is there such a limit?

72h

Why is biofiltration considered an effective LID treatment?

-physical filtration —> porous medium 

- which is biochemically active

List the following LID treatment approaches from perceived most effective to least: hydrodynamics, physical filtering, biofiltration, settling, deep infiltration

-deep infiltration (100% treatment)

-biofiltration

-physical filtering

-settling

-hydrodynamics

Describe the following LID design process element: distributed management

Treat Stormwater Control Measures  locally, in smaller units,

managing stormwater as close to the source as possible

Describe the following LID design process element: minimize full connectivity

involves breaking the direct flow paths of stormwater across impervious surfaces to reduce runoff volume, peak flows, and pollutant transport

Give an example of a contaminant hotspot.

Concrete pad under a dumpster

Describe the following LID design process element: minimize direct outflows

keep runoff on-site longer and treat it before discharge

What is the general design problem with SCM inlet transitions?

-high velocity inflow ===> slow+spread

-inline or offline (until this??)

-outflow control

        -– normal events

         – extreme events

– storage volume
                            – above ground ⇒ basin
                            – in coarse medium

– underdrain
                          – where discharge?
– vegetation growth medium

What is the primary difference between the 2010 Tennessee Permanent Stormwater Management General Permit and the 2016 and 2021 Permits?

The 2016 and 2021 permits seek to retain and infiltrate a 1-inch of storm whiles attenuating peak runoff rate. The 2010 focused on just the latter

In STAR each element has 4 characteristics the user must define.  List two of those.

Surface area

Management/SCM

Underlying soil 

Routing

Some infiltration models use the “coefficient approach” based on a large national database holding measured results from many different SCMs in various locations. The lecture mentioned 5 problems with that approach.  List two of those.

Differences expected from intensity

Differences expected from location

The STAR approach models infiltration based on the Kostiakov-Lewis model and data that were collected for that.  Why?

aaa

The STAR approach adjusts the Kostiakov-Lewis model infiltration results for management based on combining it with data from what other hydrologic model?

Curve Number Method

In the discussion of the new 2021 TN Permit, I mentioned a problem with the general approach of adjusting the treatment volume.  What is the issue?

fa

In the discussion of the new 2021 TN Permit, I mentioned that the Permit sets the design storm to a 1-yr 24-hr event, but does not define a storm intensity distribution.  What is the issue with just assuming a Type II distribution?

fqa

  In the discussion of the new 2021 TN Permit, I mentioned that the Permit clearly attempts to penalize the “flow-through” treatments (filtering and hydrodynamic) by defining larger Water Quality Treatment Volumes for those.  What is the problem with this?

vaa

What two processes generally cause detachment on the hillslope?

raindrop impact

runoff energy 

Why can very shallow flow in the sheet erosion areas still transport detached particles?

ada

Is detachment by raindrop impact generally fairly even across the slope, or concentrated?

Detachment by raindrop impact is concentrated at the top of the slope

Is detachment by runoff flow energy generally fairly even across the slope, or concentrated?

Moving downslope, detachment by runoff flow energy becomes concentrated in small areas causing rills.

What is the primary form of detachment in rills?

Runoff jets

What will generally happen if transport capacity > sediment load?

Erosion occurs. Channel deepens or widens

What will generally happen if transport capacity < sediment load?

Sedimentation or settling

Describe for clay particles the ease of detachment and ease of transport

Clay particles are hard to detach but easier to transport because of the size

Describe for silt particles the ease of detachment and ease of transport

Worst- slightly easy to detach and moderately easy to transport

Describe for sand particles the ease of detachment and ease of transport

Easy to detach, hard to transport

Describe the detachment and transport processes occurring in sheet erosion areas.

Detachment is by rain impact and transported by runoff

  Describe the detachment and transport processes occurring in sheet & rill erosion areas.

As we move downslope, we tend to get small concentrated areas of runoff and then we start getting detachment from runoff jets forming little channel called rills and then sheet erosion forms in between

We mentioned three characteristics of rills.  List two of those.

-roughly parallel

-from sheet areas to bottom of hillslope

-position controlled by microtopography
          —random

How is the concentrated flow channel at the bottom of the hillslope different from the rills on the hillslope?

They form downcutting, sidewall sloughing and headcut

What rainfall factors control erosion?

-depth

     → raindrop impact

-intensity

      → runoff depth
  → runoff rate

Which has the highest erosion, if all three have the same overall slope length and steepness:  a slope that is planar, convex up, or concave up, and why?

Convex because we have more runoff at the steepest part

We mentioned four general ways in which wind erosion is far harder to understand and measure than is water erosion.  List two of those.

No defined path

No windshield 

combination of 2D and 3D

There are three main problems associated with using before / after surface elevation measurements to define erosion.  List two of those.

  issues-

-number of points required
-scale too small

-what is substance?
          -settling?
          -OM (organic matter)

There are four erosion parameters commonly measured that are used in erosion models.  List two of those

-surface cover

-surface roughness

-canopy cover

-topography

What drop size distribution are we usually trying to get with rainfall simulators?

natural drop size distribution (not sure)

Why do raindrops tend to get larger in more intense rainfalls?

In more intense rainfall, larger raindrops form because there's more moisture, stronger updrafts, and more frequent droplet collisions — all of which allow raindrops to grow bigger before falling to the ground.

For rainfall simulators that use a single rainfall intensity, what is the normal value used (in iph), and on what is that based?

2.5 iph ⇒ single intensity ; realistic intensity (not sure) to represent high intensity, short duration storm

The USLE / RUSLE is based on a dataset that was initiated by what USDA employee?

Walt Wischmeier (not sure)

The USLE / RUSLE is based on how much data (include specific units)?

What erosion does RUSLE model?

RUSLE has the form A = R K LS C P.  Describe A and R.

A= soil detachment (units: M L⁻² T⁻¹)

R = rainfall erosivity (complicated units)

US⇒

10 /yr in desert

700 /yr in Miami

2000 /yr in Hawaii

RUSLE has the form A = R K LS C P.  Describe K and LS.

K = soil erodibility

       -units balanced on R to give A ⇒ M·L⁻²·T⁻¹

        -units of erosion / unit erosivity

        -  0.2 → 0.5

                  LS = topography

●      0 → 200

RUSLE has the form A = R K LS C P.  Describe C and P.

C = cropping-management

●      broad area

●      0 → 1

P = conservation practices

If the RUSLE R factor for a city is 5 times the size of the R factor for Knoxville, how would we expect the erosion in that city to differ from that in Knoxville if all other factors re the same?

What does the Unit Plot represent?

Wischmeier found an 82% correlation between measured Unit Plot erosion and what combined rainfall value?

R+A

How is the RUSLE K factor measured?

In RUSLE, the C factor has the form C = SC CC SR PLU SM. Describe SC and CC.

In RUSLE, the C factor has the form C = SC CC SR PLU SM. Describe SR and PLU.

With % surface cover on the x axis and the SC subfactor on the Y axis, put values on the axes and draw the SC curve.

RUSLE does best in estimating erosion within what range?

best for midrange ~20 T/A/yr

Why does RUSLE not work for long-term undisturbed pasture and forests?

Why does RUSEL not do well with the usual low-resolution topographic information often available in GIS packages?

What two factors determine if a river is stable or unstable?  

balance of 2 things:

-sediment load(resistance): bed load, sediment size

-hydrologic load(energy): stream slopes discharge

How do changes in sediment load affect a river's equilibrium according to Lane's Balance?

Increase in sediment load increases deposition. Because the capacity of stream is less than the sediment load it's receiving. When capacity>load, erosion occurs. 

What factors can a river adjust to regain equilibrium after a change in sediment load?

changes the width or depth or bedford charcteristics

To regain equilibrium after a change in sediment load, a river can adjust its channel geometry, slope, and/or hydrologic load. 

What are the characteristics of a stable river channel?  

Stable river: balance hydrologic forces & resisting forces

         -Stable rivers migrate slowly over long periods of time.
         -Features like pools/riffles that help to distribute energy, prevent excessive erosion, & support biodiversity.

31.  What are some triggers for instability in rivers?  

Triggers: land use change, dam operations (changes in flow), channel straightening,

Describe headcutting and its features.  

Headcut: abrupt vertical drop in a channel – a localized erosion feature

Describe downcutting and its features.  

Downcutting: vertical erosion that deepens a channel

Does erosion in rivers tend to occur outside meander bends or inside?  Why?

Erosion occurs on the outside of the bends.

This is due to faster, more energetic flow and higher shear stress, while the inside of the bend is where flow slows and sediment is deposited

What are the indicators of movement in a stream that is in dynamic equilibrium?

Indicators of dynamic equilibrium

●      Sediment transport & supply are balanced

●      Consistent form/function over time

●      Alternating sequences of riffles/pools

●      Floodplain connectivity

●      Vegetated banks that are stable