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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 a number 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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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…. τ = ρgds

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

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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 6 th order stream 3 5 th order 9 4 th order27 = 3 27 3 rd order9 81 2 nd order 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

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V. Basin Evolution and Denudation

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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

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

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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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0.398 km 2

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BeforeAfter ?? ?

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13, 364 m 3 0.398 km 2

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Volume = 13, 364 m 3 Area 0.398 km 2 or 398,000 m 2 = 0.034 m = 3.4 cm

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Summary of Basin Denudation of Blue Ridge Systems Event Basin Basin Area (km 2 ) Volume of Sediment Eroded (m 3 ) Mean Basin Denuda- tion (cm) Hurricane Camille Willis Cove 4.08173,4884.25 Hurricane Camille Ginseng Hollow 1.7588,7275.07 Hurricane Camille Polly Wright Cove 2.4787,7073.55 Rapidan Flood Jenkins Hollow 0.39813,3643.36 Rapidan Flood Teal Hollow0.1232,4922.03

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Hurricane Camille Rapidan Storm

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

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VI. Basin Hydrology A. Subsurface Water Hydrogeology (GEOL 460) M W 10:10-11, Friday Lab

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VI. Basin Hydrology A. Subsurface Water Hydrogeology (GEOL 460) M W 10:10-11, Th lab

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VI. Basin Hydrology B. Surface Water 1. Terms Discharge Q = V * A

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

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

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3. Flood Frequency

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What does this mean???

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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: a 50 year flood has an 86% chance of occurring over 100 years CAUTION!!! ANALYSIS GOOD FOR 1.5x length of data set

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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

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

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

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