1. Introduction to River Systems
ENVIRONMENTAL GEOLOGY
Introduction to River Systems
This powerpoint can be used to review (or introduce students to) river systems and familiarize students with the kind of data they will be working with for the “From Source to Sink…” mini-lesson. Some of the river variables, such as length and velocity, are pretty straightforward and may not need to be covered at all. This powerpoint does not include information about floodplain development or meander migration, but simply introduces students to what a floodplain is. Variables such as sediment yield are less intuitive and instructors should be sure that students understand how these are determined for given river systems.
Image of navigable river systems from Joint Research Centre of European Commission:
Navigable rivers were extracted from the CIA World DataBank II, which is a collection of world map data, consisting of vector descriptions of land outlines, rivers, and political boundaries. It was created by the U.S. government in the 1980s and has a nominal scale of 1:5,000,000.  Travel speeds: Navigable rivers, 20km/hr = 3 min per km.  Source:  Further information: Gorny, A. J., and R. Carter World Data Bank II General User's Guide, Central Intelligence Agency, Washington, DC, USA. 
Velocity and discharge
Length and gradient
Channel and floodplain development
Drainage area
Sediment yield
LECTURE 6

2. ENVIRONMENTAL GEOLOGY
River Velocity
Image of the Breakers rapid in summer spate, River Ayr, at Oswald Hall Auchincruive from Wiki commons.
Velocity  ft/sec or m/s (V)
Average velocity  ū
Rivers and Streams

3. ENVIRONMENTAL GEOLOGY
River Discharge
Volume rate of water flow through a cross-sectional area
Units of m3/s (cubic meters per second) or ft3/s (cubic feet per second or cfs)
The variable Q is used for discharge, and can be approximated by multiplying the channel width and depth (cross-sectional area) by the water velocity. Because flow velocity at any one point within the cross-sectional area of a river may be different, discharge may calculated by summing discharge calculated for subsections of the channel (pictured in diagram), or by using the average flow velocity within the cross-sectional area:
Q = Aū
Where
Q is the discharge (m3/s or ft3/s or cfs)
A is the cross-sectional area of the portion of the channel occupied by the flow (m2 or ft2)
ū is the average flow velocity (m/s or ft/s)
Image from The hydrologist pictured is conducting a routine stream measurement that involves measuring the velocity of water flowing at numerous locations across the stream. At each location he also measures velocities at a number of vertical points, too. From these velocities, the total amount of water per second flowing by can be calculated.
Credit: USGS
Diagram from
LECTURE 7

4. ENVIRONMENTAL GEOLOGY
River Gradient
Longitudinal
Profile:
Cross-sectional
Profiles:
Image from The British Geographer webpage about river processes:
Gradient  vertical drop / horizontal run [slope]
- Note: gradient usually decreases with distance from source
- Overall Shape: concave upward
LECTURE 7

5. Channel and Floodplain Development
ENVIRONMENTAL GEOLOGY
Students need to understand what a floodplain is and how it develops; the activity describes floodplains around river channels at < 0.1 gradient, so these are broad, nearly flat regions. Large floodplains tend to develop in low-gradient sections of rivers.
Image: This highly detailed true-color image shows the stark eastern edge of the Zambezi floodplain. To the left of the edge, water covers everything. Deep blue channels wind among green, shallowly flooded plains. To the right of the edge, the land is dry. The city of Kasane is perched confidently along the edge of the flood plain. Image from NASA Earth Observatory: zambezi_ali_ _lrg.jpg.
LECTURE 7

6. ENVIRONMENTAL GEOLOGY
Drainage Area
A drainage area is the area of land within which surface water converges to a single point at a lower elevation, typically exiting the drainage basin, such as another water body (a larger river, a lake or the ocean). Drainage basins are hierarchical, with smaller drainage basins included within larger drainage basins. For example, the Illinois River has a small drainage area that is included within the larger Mississippi River drainage area. Drainage area is also referred to as drainage basin, catchment area, catchment basin, and river basin. The units for drainage area are km2 (square kilometers).
Image of Mississippi river basin from Wiki Commons.
LECTURE 6

7. ENVIRONMENTAL GEOLOGY
Sediment Yield
Total sediment exported from a drainage basin to the continental margin
Volume or weight of sediment per unit area of drainage basin
Sediment yield is the total amount of erosional debris exported from a drainage basin. It is expressed as either a volume or a weight per unit area of a given drainage basin. Sediment yield is measured over several years, and is therefore an annual average. Sediment yield is determined by dividing the total sediment load at the river mouth by the drainage area of the river system; dividing by the drainage area serves as a normalizing factor to account for the very different sizes of drainage basins.
Image of Yangzte River Delta and sediment discharge from NASA; taken from the Encyclopedia of Earth web page:
LECTURE 7