EART 204 Water - websites.pmc.ucsc.edu
Transcript of EART 204 Water - websites.pmc.ucsc.edu
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EART 204
Water
Dr. Slawek Tulaczyk
Earth Sciences, UCSC
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Water is an amazing liquid, (high heat capacity - particularly in phasetransitions, maximum density at ca. 4 deg. C)
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Basin Hydrologic Cycle
Charbeneau, 2000.
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Basin Hydrologic Cycle – GW/SW Interaction
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Global Hydrologic Cycle – Schematic
Domenico and Schwartz, 1990.
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Basin Hydrologic Cycle – Schematic
Domenico and Schwartz, 1990.
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Basin Hydrologic Cycle – Quantitative Representation
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Basin
Aquifer
Surface/Soil
Domenico and Schwartz, 1990.
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2. Soil Horizons
16Charbeneau, 2000.
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Figure 15.1
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3. Aquifers
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Aquifers
Definition: A geological unit which can store andsupply significant quantities of water.
Principal aquifers by rock type:UnconsolidatedSandstoneSandstone and CarbonateSemiconsolidatedCarbonate-rockVolcanicOther rocks
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Occurrence of GroundWater
• Ground water occurswhen water rechargesthe subsurface throughcracks and pores in soiland rock
• Shallow water level iscalled the water table
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Recharge
Natural• Precipitation• Melting snow• Infiltration by streams
and lakes
Artificial• Recharge wells• Water spread over land
in pits, furrows, ditches• Small dams in stream
channels to detain anddeflect water
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Example Layered Aquifer System
Bedient et al., 1999.
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Other Aquifer Features
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• Leaky confined aquifer: represents a stratum thatallows water to flow from above through a leakyconfining zone into the underlying aquifer
• Perched aquifer: occurs when an unconfined waterzone sits on top of a clay lens, separated from themain aquifer below
Leaky and Perched Aquifers
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4. Soil Texture
26Bedient et al., 1999.
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Well sorted fine sand
Poorly sortedsilty fine to
medium sand
Particle Size Distribution
Bedient et al., 1999.
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Particle Size Distribution
Charbeneau, 2000.
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4. Porosity and Density
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REV – Representative Elementary Volume
Charbeneau, 2000.
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REV – Scale Effect
Freeze and Cherry, 1979.
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Types of Porous Media
Freeze and Cherry, 1979.
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Typical Values of Porosity
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6. Saturation and Water Content
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Soil Moisture Held by Capillary Pressure
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Moisture Content in Capillary Zone
Charbeneau, 2000.
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7. Hydraulic Head
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Pressure and Elevation Heads - Laboratory
Freeze and Cherry, 1979.
ψ = pressure headz = elevation headh = total head
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ψ = pressure headz = elevation headh = total head
Pressure and Elevation Heads - Field
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Two Confined Aquifers with Different Heads
Charbeneau, 2000.
Groundwater will tend toflow from the top aquiferto the bottom aquifer.
We can’t make anyconclusion abouthorizontal head gradientsfrom this picture.
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Horizontal and Vertical Head Gradients
Freeze and Cherry, 1979.
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Horizontal and Vertical Head Gradients
Freeze and Cherry, 1979.
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Hydrologic Cycle and Water Distribution
Bedient et al., pp. 1-6
Domenico & Schwartz, pp. 9-21
Soil Horizons
Bedient et al., pp. 15-18
Charbeneau, pp. 5-6
Aquifers/Soil Texture/Porosity and Density/Saturation and Water Content
Bedient et al., pp. 18-23
Charbeneau, pp. 2-12
Hydraulic Head
Bedient et al., pg. 24
Domenico and Schwartz, pp. 58-59
Freeze and Cherry, pp. 18-25
Lecture 2Reading Assignments
Note: Only reading in Bedient et al. is required. Other reading assignments are highlyrecommended and contain extended explanations that might be helpful for your understanding ofthe material.
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Hydrology
• Hydrologic Cycle• Precipitation
– Average over Area– Return Period
• Abstractions from Rainfall• Runoff
– Hydrographs– Determination methods
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Hydraulics of Structures
• Weir flow• Orifice flow• Pipe flow• Spillway flow
– Stage-Discharge relationship
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Open Channel Flow
• Channel geometries– Triangular– Trapezoid– Parabolic
• Manning’s equation– Manning roughness, “n”
• Grass waterway design
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Precipitation
• Input to the Rainfall-Runoff process• Forms include:
– Rainfall– Snow– Hail– Sleet
• Measured directly• Varies temporally and areally
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Rainfall Data
• Daily• Hourly• 15-minute• Continuous• Reported as depth, which is really volume
over a given area, over a period of time
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Average Rainfall
• Simple arithmetic average• Theissen Polygon
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Example 1How do different calculation methods of rainfall average compare?
Consider:
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US 100yr-24hr Rainfall
100yr-24hr data from TP-40 (Hershfield (1961) as referenced by Fangmeier et al. (2006)
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Runoff
If rainfall rate exceeds the soil infiltration capacity,ponding begins, and any soil surface roughnesscreates storage on the surface. After at least someof those depressions are filled with water, runoffbegins. Additional rain continues to filldepressional storage and runoff rate increases asmore of the hill slope and subsequently thewatershed contributes runoff.
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Rainfall/Runoff process
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Open Channel Flow
Flow through open channels is anotherimportant area to consider and review.Velocity and flow rate are usuallycalculated using Manning’s equation, whichconsiders flow geometry, channel roughnessand slope.
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Manning’s Equation
Where:
V= flow velocity in fpsRh = Hydraulic Radius in ftS = Energy gradeline slope in ft/ft (=bed slope for normal flow)n = Manning coefficient1.49 = conversion from SI to English units
Hydraulic radius is the flow area divided by the wetted perimeter.
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Open Channel Flow – Channel Geometry
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Manning “n” values
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Example
What is the flow rate for a rectangular finished(clean) concrete channel with a base width of 8’,channel slope of 0.5%, with a “normal” waterdepth of 2’?
A: 140 cfsB: 8.5 cfsC: 100 cfsD: 200 cfs
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Solution
n is 0.015, Rh is 8*2 sq.ft./(2+8+2) ft, S is 0.005 ft/ft, soV = 8.5 ft/sec
Q = V*A= 8.5 ft/sec*16 sq.ft. = 140 cfs