Rivers to the Ocean
Texas Waters, Rivers and the Gulf of Mexico
The Water Cycle - Nature’s Recycling System
• Water is essential for all life on Earth.
• Water occurs as a liquid, a solid, and a gas.
• Water is constantly recycled.
• Most of the water on Earth is in the oceans.
Watersheds feed
our water supply
A watershed is an area of land that drains downward into a common area.
All land can be divided into watersheds.
Groundwater
Surface water
(aquifer)
(streams, rivers, lakes and ponds)
Rain and runoff seep under
ground into aquifers.
Rain and emerged spring water
run down across the land into
streams, rivers, lakes and ponds.
Texas Sources of Fresh Water
Surface water
Rivers, streams, lakes make
up river basins
Groundwater
Over half of Texas’ water needs are
met by underground aquifers.
Springs
Springs bubble up to the surface from groundwater.
Spring are often the home of unique plants and animals.
Some rivers start as springs.
Wetlands
Examples of wetlands are
freshwater and saltwater
marshes, swamps, lagoons,
bogs, and playas or prairie
potholes. There are even
wetlands in the desert.
Freshwater Wetland
Wetlands provide habitat,
protect water quality, prevent
flooding, control sediments,
and support aquatic life.
Coastal Wetland
In Texas, Rivers Flow to the
Gulf of Mexico
Rivers provide fresh water to
the salty ocean.
The zone where fresh river
water mixes with the salty
ocean is called an estuary
or bay.
A mix of freshwater and
saltwater in estuaries is
needed to help much of
our seafood, saltwater
sportfish, crabs and shrimp
reproduce and grow.
Nueces Bay
Red Drum
Blue Crab
Hermit Crab
Gulf Shrimp
Saltwater in the Gulf
Most of the water on
Earth (97%) is salty.
The water that we drink
is freshwater. Less
than 1% of the
Earth’s water is
available for drinking.
Saltwater in the Gulf of
Mexico is home to a
diversity of life.
Rivers: from Source to Coast
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:
• 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
UPPER COURSE
Biological Changes:
• 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
Physical Changes:
• 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
MIDDLE COURSE
Biological Changes:
• 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
Physical Changes:
• 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
LOWER COURSE
Biological Changes:
• Little to no tree canopy
• Aquatic plants absent from main
channel
• Lots of phytoplankton
• Low diversity of aquatic insects;
more mollusks
• Fish largely planktivores