Steve Hubbs & Tiffany Caldwell University of Louisville Clogging in Louisville.
Post on 26-Dec-2015
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- Steve Hubbs & Tiffany Caldwell University of Louisville Clogging in Louisville
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- 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.
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- Typical RBF systems in US Smaller system capacity (5,000 m 3 /day) Recent tendency for large systems (100,000 m 3 /day) and larger Located very close to streams (30 meters from bank) Laterals extend under riverbed
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- 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
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- RIVERBANK FILTRATION An effective technique for public water supply An ancient technologydocumented 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
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- 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.
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- 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
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- Factors Restoring Yield Riverbed shear stress and scouring Biological Grazing (Rhine River) Mechanical Intervention (Llobregat River)
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- 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.
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- Predicting Sustainable Yield Use a combined stochastic/deterministic approach. Specific Capacity = Flow/(river head - well head) C s = a*(river temp) + b*(well temp) + c*(time)
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- Raw Data for Regression Model
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- Model with Temperature only
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- Regression Model, cleaned data
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- Projection of Model-20 years
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- September 9, 2004
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- 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
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- Projection with Jumps-capacity in MGD August 2004 (predicted) Specific Capacity:Measured: 0.545 MGD/ft Predicted: 0.36 MGD/ft measured
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- 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.
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- Pump Tests at LWC 1999 Pump test 2004 Pump test Direct measures of infiltration
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- 20 MGD Collector Well: Ohio River at Louisville
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- Measured 2 feet below riverbed
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- 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) P39 1999
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- 2004 pump test repeat
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- 0.6 meter below surface
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- 3 meters below surface
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- Whats going on?
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- Ohio River Lateral L-4 Geokon Probe P37 t=20 min t=2 days BEDROCK Sand and Gravel Aquifer Piezometric surface Geokon Probe P39
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- Ohio River Lateral L-4 Geokon Probe P37 t=20 min Several months BEDROCK Sand and Gravel Aquifer Compressed Riverbed Piezometric Surface
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- 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.
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- 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
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- 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
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- Seepage meter can Hose to Attach to Bladder In Stilling Well
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- Stilling Well
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- Ohio River Lateral L-4 Geokon Probe P37 t=20 min Several months BEDROCK Sand and Gravel Aquifer Piezometric Surface No fluxArea of high flux measurement
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- 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/h L )(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
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- 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
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- 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!
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- Results of Penetrometer Riverbed surface varies considerably. Drift pin penetrates up to 0.33 meters in undisturbed areastypical 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.
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- 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 m 3 /day to 225,000m 3 /day) Using vertical wells (as opposed to horizontal collectors)
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- 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?
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- Laterals located near the bottom of this layer
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- Velocity profiles from Doppler data (USGS)
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- 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.
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- 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.
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- 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
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- Future Work at LWC Direct measure of riverbed conductivity Analysis of additional streams under varying conditions Influence of barges?
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- 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
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- 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). Riverbed Scouring
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- Comparison of Models
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