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Steve Hubbs & Tiffany Caldwell University of Louisville

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Clogging in Louisville. Steve Hubbs & Tiffany Caldwell University of Louisville. This presentation:. Provide some slope data from US Rivers. Present calculations for Specific Capacity and decrease with time at Louisville (clogging).

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slide1

Clogging in Louisville

Steve Hubbs &

Tiffany Caldwell

University of Louisville

this presentation
This presentation:
  • Provide some slope data from US Rivers.
  • Present calculations for Specific Capacity and decrease with time at Louisville (clogging).
  • Analyze Pump Test data from 1999 and 2004 for indications of Riverbed compression at Louisville.
  • Analyze field data for flux and head
  • Review calculations of riverbed hydraulic conductivity (K) for 1999 and 2004 at Louisville.
typical rbf systems in us
Typical RBF systems in US
  • Smaller system capacity (5,000 m3/day)
  • Recent tendency for large systems (100,000 m3/day) and larger
  • Located very close to streams (30 meters from bank)
  • Laterals extend under riverbed
sites with rbf systems
Sites with RBF Systems
  • Louisville, 20 MGD (45 MGD planned), Ohio River
  • Cincinnati, 30 MGD, Great Miami River
  • Somoma, CA. 45 MGD, Russian River
  • Lincoln NE, xx MGD, Platte R
  • Des Moines, KC,
  • Considering: St.Louis, New York, others
riverbank filtration an effective technique for public water supply
RIVERBANK FILTRATIONAn effective technique for public water supply
  • An ancient technology…documented in the Bible!
    • Exodus 7:24 “…dug around the Nile for water to drink.  Filtered through sandy soil near the river bank, the polluted water would become safe to drink.”
  • Modern installations in Germany over 140 years old
  • Extensive development in US since the 1950s
  • Recent interest as a treatment technique for Disinfection By-Product and Pathogen Regulations
indications of clogging
Indications of Clogging
  • Louisville capacity decreases to 67% of original level over 4 years, hardpan present.
  • Cincinnati “hardpan” forms when pumping at high levels under low-stream flow conditions
  • Sonoma infiltration beds hard to penetrate and unsaturated below surface.
  • Initial capacity of collector wells decrease after several years of operation.
factors impacting yield
Factors Impacting Yield
  • Temperature (River, Aquifer, Well)
  • Time (used as a surrogate for plugging)
  • Pumping Rate and Driving Head
  • Aquifer Characteristics (at riverbed, through bulk of aquifer, near wellscreen)
  • Water Quality
factors restoring yield
Factors Restoring Yield
  • Riverbed shear stress and scouring
  • Biological “Grazing” (Rhine River)
  • Mechanical Intervention (Llobregat River)
sustainable yield
Sustainable Yield
  • The long-range sustainable yield is a balance between all yield-limiting factors and all yield-restoring factors
  • The question is: How do we measure and predict all of these factors?
  • Focus of this part of the presentation: looking at the composite of plugging factors, and the impact of shear stress on sustainable yield.
predicting sustainable yield
Predicting Sustainable Yield
  • Use a combined stochastic/deterministic approach.
  • Specific Capacity = Flow/(river head - well head)
  • Cs = a*(river temp) + b*(well temp) + c*(time)
impact of 4 month layoff 2004
Impact of 4 month layoff, 2004
  • Pump failures resulted in long downtime
  • Pumps off during high flow events of spring 2004
  • Pumps restarted July 28, 2004
  • Pump test of 1999 repeated
projection with jumps capacity in mgd
Projection with Jumps-capacity in MGD

Specific Capacity:

Measured: 0.545 MGD/ft

Predicted: 0.36 MGD/ft

August 2004 (predicted)

measured

specific yield calculations
Specific Yield Calculations
  • Adjusting for temperature, the calculated specific capacity for 2004 is 0.645 MGD/ft at week 4 of pump test.
  • A similar calculation for specific yield was 0.848 for 1999 after week 4 of pumping.
  • Current capacity approximately 76% of original after layoff and scouring event.
  • Previous measurements indicated that capacity was approximately 67% of original.
pump tests at lwc
Pump Tests at LWC
  • 1999 Pump test
  • 2004 Pump test
  • Direct measures of infiltration
slide29

1999

P39

The aquifer velocity q is measured

at the mid-point of curve at W1 (P39)

at 1.08 hours for the 2 foot distance

or 2 feet/hour

The measured head loss at P39 was

10 feet across the 2 foot vertical distance

yielding a riverbed K value of:

K=(2’/10’)(2ft/hour)=0.4 ft/hr (0.12m/hr)

slide37

Ohio River

Geokon Probe P39

t=20 min

t=2 days

Geokon Probe P37

Sand and Gravel Aquifer

Lateral L-4

BEDROCK

Piezometric surface

slide38

Compressed Riverbed

Ohio River

t=20 min

Geokon Probe P37

Sand and Gravel Aquifer

Several months

Lateral L-4

BEDROCK

Piezometric Surface

interpretation of 2004 temp data
Interpretation of 2004 Temp data
  • Pump test starts with aquifer saturated to 420’.
  • As head increases, vertical velocity increases and piezometric surface drops.
  • After 8 hours, the piezometric surface intersects and drops below the riverbed. Riverbed conductivity reduces sharply, and the flow path shifts from vertical to horizontal.
  • The piezometric surface continues to extend, increasing the distance of flow and bringing in cooler aquifer water. Minimal flow is passing P39.
  • The piezometric surface stabilizes, and temperature increases to river temperatures.
direct measure of riverbed flux rate
Direct Measure of Riverbed Flux Rate
  • Seepage meter procedure modified for deep river use
    • Heavy “can” 1 sq. foot surface (0.093 sq meter)
    • Flexible connection to surface
    • Stilling well at river surface
    • Camera to observe riverbed conditions
problems with flux measurement
Problems with flux measurement
  • Wind, Waves, and Current are enemies
  • Unable to work when river velocity exceeds 1 mph (1.6 km/hour) due to erosion of seal
  • Wind/waves make boat and stilling well pitch
  • It takes near-perfect conditions to get repeatable data
slide45

Hose to

Attach to

Bladder

In Stilling

Well

Seepage meter

“can”

slide48

Ohio River

t=20 min

No flux

Area of high flux measurement

Geokon Probe P37

Sand and Gravel Aquifer

Several months

Lateral L-4

BEDROCK

Piezometric Surface

calculating riverbed k from direct measurement of infiltration rate
Calculating Riverbed K from direct measurement of infiltration rate
  • Approach Velocity measured at .3 to 1 meter/hour
  • Porosity assumed at 0.2
  • Aquifer velocity q = (.3/0.2) = 1.5 m/hour
  • Head loss across riverbed at 0.6 meter depth is 6 meters
  • K=(L/hL)(q)= (0.6/6)1.5m/hour = 0.15 m/hr
  • Measured range based on approach velocities was 0.15 to 0.45 m/hour
summary of measured riverbed k values
Summary of Measured Riverbed K values
  • At identical points (P39, 0.6m depth)
    • 1999 temperature-derived value = 0.12 m/hr
    • 2004 temperature-derived value = 0.03 m/hr
  • From direct measure of flux across riverbed
    • Max 2003 flux-derived value = 0.45 m/hr
    • Typical 2004 flux-derived value = 0.15 m/hr
    • Max 2004 flux-derived value = 0.38 m/hr
measuring riverbed compression
Measuring Riverbed Compression
  • 0.33 meter Drift Pin attached to 1 meter rod
  • Dropped a distance of 0.58 meters.
  • Penetration into riverbed observed by underwater camera.
  • Submerged trees are the enemy!
results of penetrometer
Results of Penetrometer
  • Riverbed surface varies considerably.
  • Drift pin penetrates up to 0.33 meters in undisturbed areas…typical is 0.15 meters.
  • Penetration is less than 0.05 meters in areas of riverbed compression near well.
  • Additional measurements needed to define area of riverbed compression.
ongoing work at louisville
Ongoing Work at Louisville
  • Mapping infiltration rates.
  • Mapping riverbed compression area.
  • Proceeding with expansion of wellfield from 20 MGD to 60 MGD total capacity (75,000 m3/day to 225,000m3/day)
  • Using vertical wells (as opposed to horizontal collectors)
discussion
Discussion
  • Any other observations regarding compression of riverbed?
  • Do the values of riverbed “K” look right?
  • Any other theories about riverbeds under unsaturated conditions?
  • Guidance regarding design and operation of RBF systems with regards to unsaturated conditions under the riverbed?
assumptions problems in velocity profile measure of shear stress
Assumptions/Problems in Velocity Profile measure of Shear Stress
  • Uniform bed surface and predictable interface velocities based on particle size.
  • Theoretical curve based on uniform flow (and implications from river bedforms)
  • Doppler velocities limited by technique: unable to read velocities at the top and bottom 5 feet of the profile.
stream slope calculations for shear stress
Stream Slope Calculations for Shear Stress
  • Data available from USGS via internet.
  • Variety of stream flow conditions available.
  • Yields an averaged shear stress for a particular stream reach.
  • Influenced by stream characteristics: bedforms, obstructions, curves.
inferring maximum shear stress by bedload transport
Inferring Maximum Shear Stress by Bedload Transport
  • Larger shear stresses required to move larger rocks.
  • Smaller shear stresses required to move gravel and sand.
  • Data available to indicate minimum shear stress to move riverbed particles: sand 0.2 Newtons/sq. meter; gravel 3 N/sq. m
future work at lwc
Future Work at LWC
  • Direct measure of riverbed conductivity
  • Analysis of additional streams under varying conditions
  • Influence of barges?
shear stress definition
Shear Stress: Definition
  • Shear stress is the resistance imparted by a fixed surface (streambed) on a moving fluid.
  • This is similar to the friction forces at work in pipe headloss, and provides for the “head loss” in river system.
  • Units: Newtons/sq. meter; psi/sq. foot
riverbed scouring
Riverbed Scouring
  • Occurs when shear stress imparts a force on the riverbed adequate to move the particles of the riverbed.
  • Is a function of stream velocity at the riverbed, and the particles (size, shape, density) making up the riverbed itself (sand and gravel).
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