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The Drainage Basin

your friend, and all of its secrets

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I. Introduction

--two general relationships realized concerning drainage basins

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I. Introduction

--two general relationships realized concerning drainage basins

* streams form their valleys in which they flow

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I. Introduction

--two general relationships realized concerning drainage basins

* streams form their valleys in which they flow

* every river consists of a major stream that is fed by anumber of mutually adjusted branches that diminish in

size away from the main stem.

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I. Introduction

II. Slope Hydrology and Runoff Generation

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I. Introduction

II. Slope Hydrology and Runoff Generation

A. Basin Hydro. Cycle and Budget

Input = Output + change in storage

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I. Introduction

II. Slope Hydrology and Runoff Generation

A. Basin Hydro. Cycle and Budget

Input = Output + change in storage

Overland flow

Interflow

Baseflow

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I. Introduction

II. Slope Hydrology and Runoff Generation

A. Basin Hydro. Cycle and Budget

B. The Storm Hydrograph

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B. The Storm Hydrograph

Unit hydrograph: where the runoff volume is adjusted to

the same unit value (e.g., one inch of rainfall spread evenly

over a basin in one day

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Overland flow

Baseflow

Direct ppt

Interflow

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Basin Area

Discharge

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III. Initiation of Channels and the Drainage Network

A. The concept

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III. Initiation of Channels and the Drainage Network

A. The concept

Shear stress.

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III. Initiation of Channels and the Drainage Network

A. The concept

Shear stress.

Effects of

Vegetation.

= gds

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III. Initiation of Channels and the Drainage Network

A. The concept

Rills develop, and they begin to bifurcate

repeated divisions of single channel segments

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Rills develop, and they begin to bifurcate

repeated divisions of single channel segments

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Rills develop, and they begin to bifurcate

repeated divisions of single channel segments

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B B i M h t

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B. Basin Morphometry

refers to the geometry of the basin

Drainage Composition

refers to the distinct fabric of the drainage basin

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1. Drainage Composition

refers to the distinct fabric of the

drainage basin

Strahler (1952)

Shreve (1967)

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2. Linear Morphometric Relationships

Certain linear parameters of a basin are proportionally

related to stream order.

a. Bifurcation ratio (Rb)

streams of one order

streams of the next highest order

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2. Linear Morphometric Relationships

Certain linear parameters of a basin are proportionally

related to stream order.

a. Bifurcation ratio (Rb)

streams of one order

streams of the next highest order

Ex: 1 6th order stream

3 5th order

9 4th order 27 = 3

27 3rdorder 9

81 2ndorder

Ratio value is nearly constant between adjacent orders

AND.where geology is homogeneous, Rb = 3.0 5.0

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2. Linear Morphometric Relationships

Certain linear parameters of a basin are proportionally

related to stream order.

b. Length ratio ave length of streams of one order

ave length streams of the next highest order

Can be used to determine the average length of streams in

an unmeasured order.

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3. Aerial Morphometric Relationships

a. Drainage density (Dd)

total length of streams in basin

basin area

Reflects the interaction between geology and climate

In general.

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4. Relief Morphometric Relationships

a. Relief Highest elevation lowest elevation

Reflects the vertical dimensions of drainage basin

Includes factors of gradient and elevation

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IV. Basin Morphology and Flood Hydrograph

IV Basin Morphology and Flood Hydrograph

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IV. Basin Morphology and Flood Hydrograph

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V. Basin Evolution and Denudation

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V. Basin Evolution and Denudation

A. Factors affecting sediment yield

* climate

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V. Basin Evolution and Denudation

A. Factors affecting sediment yield

* climate

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V. Basin Evolution and Denudation

A. Factors affecting sediment yield

* basin size

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V. Basin Evolution and Denudation

A. Factors affecting sediment yield

* elevation and relief

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V. Basin Evolution and Denudation

A. Factors affecting sediment yield

* rock type

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V. Basin Evolution and Denudation

A. Factors affecting sediment yield

* Human Factor

V B i E l i d D d i

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V. Basin Evolution and Denudation

A. Factors affecting sediment yield

* Human Factor

V B i E l i d D d i

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V. Basin Evolution and Denudation

A. Factors affecting sediment yield

B. How do basins erode (denute?)

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Sediment Transport and Denudation

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0.398km2

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Before After

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Before After

? ?

?

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13, 364 m3

0.398 km2

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Volume = 13, 364 m3

Area 0.398 km2 or 398,000 m2= 0.034 m

= 3.4 cm

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Summary of Basin Denudation of Blue Ridge Systems

Event BasinBasin

Area

(km2)

Volume of

Sediment

Eroded(m3)

Mean

Basin

Denuda-tion (cm)

Hurricane

Camille

Willis

Cove

4.08 173,488 4.25

Hurricane

Camille

Ginseng

Hollow

1.75 88,727 5.07

Hurricane

Camille

Polly Wright

Cove

2.47 87,707 3.55

Rapidan

Flood

Jenkins

Hollow

0.398 13,364 3.36

Rapidan

Flood

Teal Hollow 0.123 2,492 2.03

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Long Term and Episodic Denudation

0

1

2

3

4

5

6

7

8

9

10

Nelson County Madison County

Denudation(cm)

Long Term

Episodic

3,500

Years 1 Day2,500

Years 1 Day

Hurricane

CamilleRapidan

Storm

B How do basins erode (denute?)

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B. How do basins erode (denute?)

High Magnitude

Low Frequency

Low Magnitude

High Frequency

VI Basin Hydrology Hydrogeology (GEOL 460)

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VI. Basin Hydrology

A. Subsurface WaterHydrogeology (GEOL 460)

M W 10:10-11, Friday Lab

VI Basin HydrologyHydrogeology (GEOL 460)

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VI. Basin Hydrology

A. Subsurface WaterM W 10:10-11, Th lab

VI Basin Hydrology

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VI. Basin Hydrology

B. Surface Water

1. Terms

Discharge

Q = V * A

VI Basin Hydrology

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VI. Basin Hydrology

B. Surface Water

1. Terms

Discharge

Q = V * A

Velocity is highly variable; depends where measured.

Velocity is highly variable; depends where measured

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Velocity is highly variable; depends where measured.

VI Basin Hydrology

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VI. Basin Hydrology

B. Surface Water

2. Reporting discharge

Daily vs annual discharge

mean vs median discharge

3 Fl d F

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3. Flood Frequency

y = 1708.5Ln(x) + 1705.1

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

1 10 100

RI (yrs)

Discharge(cfs)

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What does this mean???

y = 1708.5Ln(x) + 1705.1

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

1 10 100

RI (yrs)

Discharge(c

fs)

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What does this mean???

the curve estimates the magnitude of a flood that can be

expected within a specified period of time

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What does this mean???

the curve estimates the magnitude of a flood that can be

expected within a specified period of time

The probability that a flow of a given magnitude will occur during

any year is P = 1/RI.

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What does this mean???

the curve estimates the magnitude of a flood that can be

expected within a specified period of time

The probability that a flow of a given magnitude will occur during any

year is P = 1/RI.

EX: a 50 year flood has a 1/50, or a 2 percent chance of occurring

in any given year

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For multiple years:

q = 1- ( 1-1/T)n

where q = probability of flood with RI of T with a

specified number of years n

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For multiple years:

q = 1- ( 1-1/T)n

where q = probability of flood with RI of T with a

specified number of years n

EX: a50year flood has an86%chance of occurring over100years

CAUTION!!! ANALYSIS GOOD FOR 1.5x length of data set

The Mechanics of Determining RI

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g

Flood recurrence interval (R.I.)

use Weibull Method - calculates the R.I.

by taking the average time between 2 floods of equal or

greater magnitude.

RI = (n + 1) / m

where n is number of years on record,

m is magnitude of given flood

VI. Basin Hydrology

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y gy

C. Paleoflood Hydrology Slackwater deposits

VI. Basin Hydrology

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y gy

C. Paleoflood Hydrology Which one is right????

carbon is your friend