1. “your friend, and all of its secrets”
The Drainage Basin
“your friend, and all of its secrets”

5. Introduction
--two general relationships realized concerning drainage basins

6. Introduction
--two general relationships realized concerning drainage basins
* streams form their valleys in which they flow

7. 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 a
number of mutually adjusted branches that diminish in
size away from the main stem.

8. Introduction
II. Slope Hydrology and Runoff Generation

9. Introduction
II. Slope Hydrology and Runoff Generation
A. Basin Hydro. Cycle and Budget
Input = Output + change in storage

10. Introduction
II. Slope Hydrology and Runoff Generation
A. Basin Hydro. Cycle and Budget
Overland flow
Interflow
Baseflow
Input = Output + change in storage

11. Introduction
II. Slope Hydrology and Runoff Generation
Basin Hydro. Cycle and Budget
The Storm Hydrograph

12. 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”

13. Overland flow
Baseflow
Direct ppt
Interflow

15. Discharge
Basin Area

17. III. Initiation of Channels and the Drainage Network
A. The concept

18. III. Initiation of Channels and the Drainage Network
The concept
Shear stress…….

19. III. Initiation of Channels and the Drainage Network
The concept
Shear stress…….
τ = ρgds
Effects of
Vegetation….

20. III. Initiation of Channels and the Drainage Network
The concept
Rills develop, and they begin to “bifurcate”
“repeated divisions of single channel segments”

21. Rills develop, and they begin to “bifurcate”
“repeated divisions of single channel segments”

22. III. Initiation of Channels and the Drainage Network
B. Basin Morphometry
refers to the geometry of the basin

23. B. Basin Morphometry
refers to the geometry of the basin
Drainage Composition
refers to the distinct fabric of the drainage basin

24. Drainage Composition
refers to the distinct fabric of the
drainage basin
Strahler (1952)
Shreve (1967)

25. 2. Linear Morphometric Relationships
Certain linear parameters of a basin are proportionally
related to stream order.
Bifurcation ratio (Rb)
streams of one order
streams of the next highest order

26. 2. Linear Morphometric Relationships
Certain linear parameters of a basin are proportionally
related to stream order.
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 3rd order 9
81 2nd order
Ratio value is nearly constant between adjacent orders
AND….where geology is homogeneous, Rb = 3.0 – 5.0

28. 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.

29. 3. Aerial Morphometric Relationships
Drainage density (Dd)
total length of streams in basin
basin area
Reflects the interaction between geology and climate
In general….

30. IV. Basin Morphology and Flood Hydrograph

31. IV. Basin Morphology and Flood Hydrograph

32. V. Basin Evolution and Denudation

33. V. Basin Evolution and Denudation
A. Factors affecting sediment yield
* climate

34. V. Basin Evolution and Denudation
A. Factors affecting sediment yield
* climate

35. V. Basin Evolution and Denudation
A. Factors affecting sediment yield
Basin size
Elevation
Relief

36. V. Basin Evolution and Denudation
A. Factors affecting sediment yield
* rock type

37. V. Basin Evolution and Denudation
A. Factors affecting sediment yield
* Human Factor

38. V. Basin Evolution and Denudation
A. Factors affecting sediment yield
* Human Factor

40. V. Basin Evolution and Denudation
A. Factors affecting sediment yield
B. How do basins erode (denute?)

41. Sediment Transport and Denudation

42. 0.398 km2

44. Before
After ? ? ?

45. 0.398 km2
13, 364 m3

46. Volume = , 364 m3
= m
Area km2 or 398,000 m2
= 3.4 cm

47. Summary of Basin Denudation of Blue Ridge Systems
Event
Basin
Basin Area (km2)
Volume of
Sediment Eroded
(m3)
Mean Basin
Denuda-tion (cm)
Hurricane
Camille
Willis
Cove
4.08
173,488
4.25
Ginseng Hollow
1.75
88,727
5.07
Polly Wright Cove
2.47
87,707
3.55
Rapidan Flood
Jenkins Hollow
0.398
13,364
3.36
Teal Hollow
0.123
2,492
2.03

49. Hurricane
Camille
Rapidan
Storm

50. B. How do basins erode (denute?)
High Magnitude
Low Frequency
Low Magnitude
High Frequency

51. VI. Basin Hydrology
A. Subsurface Water
Hydrogeology
Offered in the Fall!!

52. VI. Basin Hydrology
A. Subsurface Water

53. VI. Basin Hydrology
B. Surface Water
1. Terms
Discharge = velocity * channel area
Q = V * A

54. VI. Basin Hydrology
B. Surface Water
1. Terms
Discharge
Q = V * A
Velocity is highly variable; depends where measured.

55. Velocity is highly variable; depends where measured.

56. VI. Basin Hydrology
B. Surface Water
2. Reporting discharge
Daily vs annual discharge
mean vs median discharge

57. Rating Curve

58. 3. Flood Frequency

59. What does this mean???
the curve estimates the magnitude of a flood that can be
expected within a specified period of time

60. 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.

61. 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

62. 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

63. where q = probability of flood with RI of T with a
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: a 50 year flood has an 86% chance of occurring over 100 years
CAUTION!!! ANALYSIS GOOD FOR 1.5x length of data set

64. The Mechanics of Determining RI
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

65. VI. Basin Hydrology
C. Paleoflood Hydrology
Slackwater deposits……

66. VI. Basin Hydrology
C. Paleoflood Hydrology
Which one is right????
“carbon is your friend”