Geography 3511: Introduction to Hydrology

Class materials are posted on the GEOG 3511 website.

The GEOG 3511 website, part of the Department of Geography website,

is located under undergrads, “Courses Current Semester”:

http://geography.colorado.edu/undergrad_program/curriculum/courses_current_semester

Then click on the link GEOG 3511. The website has:

• The class schedule (syllabus)

• Extra readings

• Lecture sets (such as the present one) to be posted about every week

Geography 3511: Introduction to Hydrology

Q: Is there math?

A: YES. Hydrology is a quantitative science. You are

assumed to know basic algebra and have the ability to

think in terms of rates of change (both in time and

space).

Q: Do you need to know some basic physics?

A: YES. Hydrology is a physical science; concepts of

energy, mass and their transfers permeate this course!

It is assumed that you have previously taken at least

GEOG 1001 and 1011.

Introduction to hydrology and the

water balance

The science of hydrology The science that describes and predicts the occurrence, circulation and

distribution of the earth’s water. There are two principal foci:

• The global hydrologic cycle: Transfers of water between the land

surface and subsurface, the ocean and the atmosphere.

• The terrestrial phase of the hydrologic cycle: The movement of water

on and under the land surface, physical and chemical interactions with

earth materials accompanying that movement, and the biological

processes that affect that movement.

Q: Why study hydrology?

A: Human systems are intimately shaped by the availability, flows and

quality of water.

• Agriculture

• Manufacturing

• Mining

• Recreation

• Human health

The science of hydrology (cont.)

Dingman 2002, Figure 1-4

The figure at left shows the

position of hydrologic science in

the spectrum of basic sciences to

water resource management.

Hydrology is an interdisciplinary

geoscience built upon the basic

sciences of mathematics, statistics

physics, chemistry and biology.

Space and time scales of hydrologic processes

Dingman 2002, Figure 1-3

Hydrologic processes encompass a

suite of space and time scales; from

thunderstorms that occur over the

course of minutes to hours and

space scales of a few kilometers to

the development of major river

basins occurring over millions to

tens of millions of years and space

scales of 1000-10,000 km.

IPCC-AR4

The challenge of water resource

management in Colorado and the

west brings home the importance of

hydrology as a field of research and

as a vocation. Most of the

precipitation in Colorado and the

west falls in the mountains and must

be diverted to where it is needed for

agriculture and other uses.

Water in the west

There is strong consensus from

different climate models that the west

will become warmer, affecting the winter

snowpack that drives water management

strategies. It may become drier as well.

Can we meet these challenges?

Office of the State Engineer, Colorado

How is the snowpack shaping up this year? Not very good

Courtesy Andrew Slater, NSIDC, based on SNOTEL data

http://www.co.nrcs.usda.gov/snow/snow/state/current/daily/index.html

Boulder Colorado water supply

The City of Boulder receives its raw water supply from:

Barker Reservoir -- 40% of the city's annual water supply

Silver Lake Watershed -- 40% of the city's annual water supply

Boulder Reservoir -- 20% of the city's annual water supply

On any given day, the city may be taking its water supply from any one of these sources or even all three.

Barker Reservoir

The Barker System was originally constructed as a hydroelectric power generation system by the Colorado

Power Company. It was later purchased by Public Service Company of Colorado, now known as Xcel

Energy. The system, consisting of the Boulder Canyon Hydroelectric Project, Barker and Kossler reservoirs

and the connecting pipelines were purchased by the City of Boulder in March 2001.

Silver Lake Watershed

The city-owned Silver Lake Watershed is located on North Boulder Creek east of the Continental Divide.

Seven reservoirs are located in the watershed. These reservoirs store water during high streamflow

periods. Water is then released during low streamflow periods to meet the water needs of Boulder.

Boulder Reservoir

The Boulder Reservoir, located northeast of Boulder, receives water from the Colorado River through the

Colorado-Big Thompson (CBT) system and the Windy Gap Project. Boulder's share of these projects is

delivered through facilities operated by the Northern Colorado Water Conservancy District (NCWCD).

Reservoirs, located on tributaries of the upper Colorado River on the western slope of the Rocky

Mountains, collect the water. The water is then delivered to the eastern slope where is treated for municipal

use at the Boulder Reservoir Water Treatment Plant.

http://www.bouldercolorado.gov

Colorado-Big Thompson project

The C-BT is the largest transmountain water

diversion project in Colorado. The water is used to

help irrigate approximately 693,000 acres of

northeastern Colorado farmland. Twelve reservoirs,

35 miles of tunnels, 95 miles of canals and 700

miles of transmission lines comprise the complex

collection, distribution and power system.

West of the Continental Divide, Willow Creek and

Shadow Mountain reservoirs, Grand Lake and

Lake Granby collect and store the water of the

upper Colorado River. The water is pumped into

Shadow Mountain Reservoir where it flows by

gravity into Grand Lake. From there, the 13.1 mile

Alva B. Adams Tunnel transports the water under

the divide to the East Slope.

Once the water reaches the East

Slope, it is used to generate electricity

as it falls almost half a mile through

five power plants on its way to

Colorado's Front Range. Carter Lake,

Horsetooth Reservoir and Boulder

Reservoir store the water. C-BT water

is released as needed to supplement

native water supplies in the South

Platte River basin.

http://www.northernwater.org/WaterProjects/C-BTProject.aspx

Colorado-Big Thompson project

http://www.ncwcd.org/project_features/cbt_maps.asp

Alva B. Adams tunnel

http://www.ncwcd.org/project_features/East_Portal1.asp

East portal of the tunnel

Excavation crews spent four years,

from 1940-1944, drilling the tunnel.

The first water flowed east in 1947.

The tunnel is named for a U.S.

senator from Colorado who played a

key role in convincing Congress to

fund and construct the Colorado-Big

Thompson Project. The Adams

Tunnel is the longest in the United

States to provide water for irrigation.

The tunnel is maintained by the U.S.

Bureau of Reclamation.

Agricultural water use in Colorado

http://www.today.colostate.edu/story.aspx?id=5066

Dan L. Perlman

The bulk of water use in Colorado is for agriculture. Crops are grown with water

transported to fields via irrigation ditches (and this water originates in the mountains)

and from groundwater. The familiar “crop circles” of Colorado and the rest of the

west reflect the use of center pivot irrigators utilizing groundwater.

Western water law: A complex issue

Water law in the west is a complex system of “prior

appropriation”. The two major concepts are: 1) a water

right is a right to the use of the water; the right is

acquired by appropriation; and 2) an appropriation is

the act of diverting water from its source and applying it

to a beneficial use.

Under appropriation doctrine, the oldest rights prevail.

The earliest water users have priority over later

appropriators during times of water shortage. Public

waters are to be used for a useful or beneficial

purpose. The appropriator can use only the amount of

water presently needed, allowing excess water to

remain in the stream. Once the water has served its

beneficial use, any waste or return flow must be

returned to the stream.

http://www.waterinfo.org/rights.html

http://www.crwcd.org/page_147

http://cechpress.com/Current_Projects.html

Properties of water • Freezing point: 0oC (273.16 K)

• Boiling point: 100oC at sea level pressure

Key point: Liquid water exists at a wide range of temperatures

• Latent heat of vaporization: 2.501 x 106 J kg-1

• Latent heat of fusion: 3.337 x 105 J kg-1

• Latent heat of sublimation: 2.834 x 106 J kg-1

Key point: Latent heat exchanges (particularly liquid-vapor and vapor-liquid) play a

prominent role global energy flows

• Density of water at 0oC: about 1000 kg m-3

• Density of ice: about 917 kg m-3

Key point: Ice floats!

• Specific heat capacity of liquid water: 4.181 x 103 J kg K-1

Key point: You can put a lot of heat into a given mass of water and get only a small

temperature change.

Water vapor is the single most important atmospheric greenhouse gas. It can act as

a strong feedback to amplify temperature change from increasing

concentrations of other greenhouse gases such s H20 and CH4

Properties of water (cont)

The water molecule is formed by two

hydrogen atoms (each with one electron in

its outer shell) and one oxygen atom, with

six electrons in its outer shell. The outer

shell of oxygen can accommodate eight

electrons and hence has two vacancies,

the outer shell of hydrogen can

accommodate two electrons and hence has

one vacancy. The vacancies of both the

oxygen and hydrogen can be mutually filled

by electron sharing, i.e., as a covalent

bond. The covalent bonds are strong.

Also, the molecular structure is asymmetric

such that is has a positively charged end

(the side where the hydrogen atoms are

attached) and a negatively charged end

(the side opposite the hydrogens),

producing hydrogen bonds between water

molecules that are absent in most other

liquids. Dingman 2002, Figure B-2

Properties of water (cont.)

http://en.wikipedia.org/wiki/Hydrogen_bond

Two water molecules can form a hydrogen bond

between them; the simple case when only two

molecules are present, is called the water dimer.

When more molecules are present, more bonds are

possible because the oxygen of one water molecule

has two lone pairs of electrons, each of which can

form a hydrogen bond with a hydrogen on another

water molecule. This can repeat such that every

water molecule is H-bonded with up to four other

molecules. Hydrogen bonding strongly affects the

hexagonal crystal structure of ice. The high boiling

point of water is due to the high number of hydrogen

bonds each molecule can form relative to its low

molecular mass. Due to the difficulty of breaking

these bonds, water has a high boiling point, melting

point, and viscosity compared to otherwise similar

liquids not conjoined by hydrogen bonds.

Water phase diagram

At the range of temperature and

pressures found on earth, water can

be found in all three phases, solid

liquid and vapor. The figure at right

shows the water phase diagram with

conditions on earth and other

planets plotted according to their

mean surface temperature and

pressure (1 atm is a pressure of one

earth atmosphere at sea level). The

lines separating the ice, water and

vapor regions of the phase diagram

represent equilibrium states; e.g., at

the line separating liquid water and

water vapor, either state exists with

equal preference. At the triple point

all three phases exist in equilibrium. Dingman 2002, Figure B-1

Temperature versus density plot for fresh water and ice at standard atmospheric pressure [from Maykut, 1985, by permission of Applied Physics Laboratory, University of Washington, Seattle, WA]. Water density increases with decreasing temperature until 3.98 deg. C. With further cooling, density decreases. Hence as a fresh water column cools from the surface, it initially sets up convection (overturning). One the entire column is at the temperature of maximum density, further cooling leads to a stable (stratified) situation (with the colder, lighter water at the top), and ice can form.

Water as a universal solvent

Water is called a universal solvent

because is dissolves more substances

(solutes) than any other liquid. This is

because it is a polar molecule, such

that it easily attracts other substances

that have a polar structure. The water

molecules surround the charged

solute; positive hydrogens close to

negative charges and negative

oxygens close to positive charges on

the solute molecule. This interaction

suspends the solute molecule in a sea

of water molecules and it disperses

and dissolves easily. Hence, wherever

water goes, it takes along dissolved

substances. http://www.brooklyn.cuny.edu/bc/ahp/SDPS/SD.PS.water.html

The water balance and principle of conservation

Conservation: inputs (I) –

outputs (O) = change in

storage (S)

I – O = ∆S

• Strictly refers to a control

volume, but often applied to a

geographic region, most

commonly a watershed

• Conservation also applies to

energy and momentum.

∆S I 0

commons.wikimedia.org

control volume

watershed

The water balance of a watershed

Inputs (I), outputs (O) and storage (S):

I: Precipitation (P)

Groundwater in (Gin)

O: Evapotranspiration (ET)

Groundwater out (Gout)

River discharge (Q)

Storage (S): In groundwater, rivers

and lakes

∆S = P + Gin – (Q + ET + Gout)

If we assume that Gin and Gout are

negligible, and that for the long-term

annual mean, ∆S is zero, then:

P = ET + Q, or ET = P - Q

Dingman 2002, Fig. 2-3 What can we usually measure?

P: rain gauges

Q: stream gauges

ET: hard to get except local values

Gin: hard to get, assume zero

Gout: hard to get, assume zero

S: often hard to get

Dimensions and Units

Length = L (meters)

Volume = V

V = L3 , typically m-3 or km-3

Mass = m (kilograms)

Density (ρ) is often assumed to be constant for liquid water (1000

kg m-3) hence water mass m = ρ V (this means that

conservation of mass also means conservation of volume)

Inputs (I) and outputs (O) are often expressed as rates of fluxes, or

volume/time (e.g., m-3 s-1); storage changes must have the

same units.

Inputs, outputs and storage changes can also be expressed as a

change in water depth (m) averaged over the watershed. Simply

divide by the area of the watershed (m-3 s-1 / m2 = m s-1). In this

case, instead of discharge Q we speak of runoff R.

A few unit conversions

One still commonly sees English units in hydrology.

One may have to convert units:

1 m = 39.36 inches = 3.28 feet

1 m3s-1 = 35.29 f3s-1

m3s-1 is often stated as cms

f3s-1 is often stated as cfs

A few other important concepts

Residence time (TR, units of time), also called turnover time, how

long on average does a given water “parcel” remain in storage.

RT= S/I = S/O (assumes that I=O, that is, steady state)

Units: S= m3, I or O = m3 s-1, hence TR= 1/s-1 = s

Assumes we can accurately measure S

Runoff ratio (R/P): fraction of precipitation that appears as runoff.

Again use long term annual means for P and R,

• Low runoff ratio: Water loss from ET is big

• High runoff ratio: Water loss from ET is small

Runoff ratio (R/P) for the contiguous United States

The runoff ratio (Panel B) is highest in

the humid Pacific Northwest and the

Northeast which are hilly with

substantial cloud cover. The pattern

for the runoff ratio broadly follows the

pattern of the aridity index (Panel A),

which is the ratio of mean annual

potential evaporation to mean annual

precipitation.

GEOPHYSICAL RESEARCH LETTERS,

VOL. 30, NO. 7, 1363,

doi:10.1029/2002GL015937, 2003

Hydroclimatology of the continental United

States, by A. Sankarasubramanian and

Richard M. Vogel

Some local numbers Middle Boulder Creek: 06725500 (Nederland)

Average Q = 54.4 cfs (ft3 s-1)

= 1.54 cms (m3 s-1)

= 4.86x107 m3 yr-1

Drainage area = 36.2 mi2

= 93.8 km2

= 9.38x107 m2

R = 4.86x107 m3 yr-1/9.38x107 m2 = 52 cm yr-1

Boulder Creek at Orodell: 06727000

Average Q = 86.1 cfs (ft3 s-1)

= 2.43 cms (m3 s-1)

= 7.7x107 m3 yr-1

Drainage area = 102 mi2

= 264 km2

= 2.64x108 m2

R = 7.7x107 m3 yr-1/2.64x108 m2 = 29 cm yr-1

Annual Precipitation (P)

Berthoud Pass: 95 cm

Niwot Ridge: 93 cm

Gross Reservoir 53 cm

Nederland 46 cm (18 in)

City of Boulder 48 cm (19 in)

Courtesy USGS