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

39Freeze and Cherry, 1979.

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