Background for Teachers

TPW Magazine, July 2010
Rivers Rock (pdf).

Rivers Rock

This month we take a look at rivers. In many ways, rivers were our first superhighways, transporting people, goods and ecological services. Others refer to rivers as the arteries or life blood of an area. For water sources and economics, early settlement patterns were typically along rivers. However you think of it, rivers are essential to our way of life.

We can think of rivers in two ways. One is looking at characteristics at a segment of a river. The other is looking at characteristics along the length of a river. Characteristics change at different parts of the river.

Anatomy of a River

Rivers are complex systems. Let's take a look at watersheds, river profiles, flow, floods and a river course.

Watersheds

Click for a larger view of a Watershed.

A watershed describes the area of land where surface water drains down toward a common place. All land can be divided into watersheds. This issue of the magazine suggests demonstrating a watershed by crumpling a piece of paper and looking for high and low points that would delineate a watershed. Watersheds carry water, store water and also carry sediment (and pollution), organisms and energy.

River Profile and Flow

It is easy to see what is happening on the surface of water, but underneath the surface are currents, eddies and deposits forming another world or movement and life. Knowing about the world under the surface will help you understand what lives there, alert you to safely cross or navigate and even identify the best places to fish.

The watershed illustration identifies how a river is formed and illustrates sources of runoff pollution. A river profile provides some insight into the flow of water currents and sediment deposits. Habitat cross-sections show the expected structure (vegetation and deposits) under water. The flood illustration shows flood plains and flood stages as well as the river flowing to the ocean. Click on the images for a better look or download a PDF to print.


Anatomy of a River Watershed PDF	Anatomy of a River Currents PDF	Anatomy of a River Habitats PDF	Anatomy of a River Flooding PDF

Floods

Floods have a purpose in the life of a river and its riparian (river or stream bank) zone. Flood plains and riparian zones are rich in nutrients, help retain soil and prevent erosion. Occasional floods contribute to the ecology of an area, supporting wetland plants and vegetation. Help your students learn more about the role of floods with Tortuga Tex.

River Course

Rivers generally begin in low-lying areas at higher elevations and flow downhill within a channel. Along their length, rivers swell in size, gather tributaries and drain an increasingly larger catchment area. Biological changes also occur along the length of a river. Rivers can be divided into three categories based on these physical and biological characteristics: Upper, Middle, and Lower.

	Physical Changes:	Biological Changes
Upper Course - headwaters	Steep slope; flow swiftly Narrow and shallow channel Bottom of coarse gravel and boulders Drains a small area Lots of shade; less variation in temperature	Abundant tree canopy Few to no aquatic plants Inputs from land important as food source (decaying organic matter) Lots of aquatic insects Cold water fish that eat insects
Middle Course - tributaries and flood plains	Gentle slope; flow reduced Channel widens and deepens Bottom of small gravel and sand Drains a larger area River begins to meander Little shade; clear water Large variation in temperature	Less Tree Canopy Lots of aquatic plants and algae Organic matter from upstream important as food source Lots of aquatic insects Warm water fish that eat insects and other fish
Lower Course flood plains and major rivers flow into estuaries	Slope and flow further reduced Substrate of mud and silt Little to no shade; small variation in temperature Water is turbid due to sediments Delta forms as river deposits sediment	Little to no tree canopy Aquatic plants absent from main channel Lots of phytoplankton Low diversity of aquatic insects; more mollusks Fish mostly eat plants