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