What is a Drainage Basin?

Drainage basinDrainage basin A drainage system which consists of a surface stream A drainage system which consists of a surface stream

or a body of surface water together with all tributary or a body of surface water together with all tributary surface streams and bodies of water. surface streams and bodies of water.

WatershedWatershed The area whose runoff flows to a particular streamThe area whose runoff flows to a particular stream

Drainage DividesDrainage Divides a watershed/drainage basin boundary of higher a watershed/drainage basin boundary of higher

elevation where water on the other side of the boundary elevation where water on the other side of the boundary flows to a different drainage basin. Watershed area is flows to a different drainage basin. Watershed area is the land enclosed by its drainage dividethe land enclosed by its drainage divide

Drainage basin, drainage divide, watershed, head waters, mouth

(see Fig. 6.2 on p. 127)

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/fluvial_systems/stream_system.html

www.mvn.usace.army.mil

(covers more than 1,245,000 square miles, includes all or parts of 31

states)

What causes streams to vary in size? Drainage AreaDrainage Area

Mississippi RiverMississippi River1,245,000 square miles1,245,000 square miles

Lumber River Lumber River 708 square miles708 square miles

ClimateClimate Precipitation/Evaporation RatesPrecipitation/Evaporation Rates

Geology/VegetationGeology/Vegetation

Stream Flow•

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/fluvial_systems/channel_geometry_and_flow.html

What factors are important to determine the flow of water in a river? Cross-sectional area of channelCross-sectional area of channel Velocity of water Velocity of water

Discharge

Q = A * VQ = A * V Q = discharge in feetQ = discharge in feet33/sec/sec A = Cross-sectional Area in feetA = Cross-sectional Area in feet22

(Channel Width x Water Depth)(Channel Width x Water Depth) V = Velocity of water in feet/secV = Velocity of water in feet/sec

The cross-sectional area (A) 10m wide by 2.5 m deep = 25 m2

And the velocity of flow (V = 5m/sec) are used to calculate discharge (Q) 25m2 x 5 m/sec = 125 m3/sec

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/fluvial_systems/channel_geometry_and_flow.html

A Gage House-the most common source of river stage data.

http://www.state.nj.us/drbc/gage/collected.htm

FIG. A. Current meter being used to measure discharge.

FIG. B. Current Meter.

FIG. C. Stage/Discharge Rating Curve

Comparison of Discharges

Mississippi River near Mississippi River near St. Francisville, LASt. Francisville, LA Area Drained: Area Drained: 1,125,300 mi1,125,300 mi22

  Mean Discharge:Mean Discharge: 543,400 ft543,400 ft33/sec/sec Lumber River near LumbertonLumber River near Lumberton

Area DrainedArea Drained 708 708 mimi22

Mean Discharge:Mean Discharge: 692 ft692 ft33/sec/sec

http://water.usgs.gov/nasqan/progdocs/factsheets/

Capacity:How much can a stream carry? Capacity is related to:Capacity is related to:

Velocity:Velocity:Discharge Discharge

• which is related to the drainage areawhich is related to the drainage areaSlope Slope

•GradientGradient

How Do You Measure Gradient?

Gradient Gradient = =

Change in Elevation / Distance:Change in Elevation / Distance:

ElevationElevation11 (Upstream) – Elevation (Upstream) – Elevation22 (Downstream) (Downstream)

Distance between points 1 and 2Distance between points 1 and 2

Profile of a typical stream showing the change in gradient downstream

(see Fig. 6.5 on p.129)

Modified from http://www.physicalgeography.net/fundamentals/10y.html

Base level

Headwaters High gradient

Low Gradient

Stream channel near the headwaters.

http://www.physicalgeography.net/fundamentals/10y.html

Stream channel near the middle of a typical stream profile.

http://www.physicalgeography.net/fundamentals/10y.html

Stream channel near the base level of a stream

http://www.physicalgeography.net/fundamentals/10y.html