Chapter 2 Flashcards
Surface water hydrology
is the study of moving water found in rivers, open channels, and runoff flowing across the open land surface
a stream is
a “flow of running water, large or small,” whereas a river is a “large stream of water.”
a stream is a “flow of running water, large or small,” whereas a river is a “large stream of water.” Most people use these terms interchangeably to denote
a body of running water of any size
Most people use these terms interchangeably to denote a body of running water of any size. However, a stream is generally considered to be smaller than a
a river, a creek smaller than a stream, and a brook even smaller
Rills form during
precipitation events
Rills form during precipitation events and gather
downhill to form a brook
Rills form during precipitation events and gather downhill to form a brook which, if it grows, creates a
creek
river and stream will be used to denote a flow of running water
large or small.
watershed
The total land area that drains surface water to a common point (or common body of water)
water shed is also called
a river basin, drainage basin, and catchment
Watersheds can be as small as a
parcel of ground that drains into a pond
Watersheds can be as small as a parcel of ground that drains into a pond or as large as
the 1.26 million square miles in the United States and Canada that drain into the Mississippi River and its tributaries.
A watershed is delineated by a
ridge or drainage divide that marks the boundary of the drainage basin and can be easily identified on topographic maps
All surface water runoff below a ridge line will flow
downhill within the watershed
The incline of terrain is generally downhill toward
the main channel of a river
The boundaries of a watershed can be delineated by
first locating the lowest point, or watershed outlet, on a topographic map.
The boundaries of a watershed can be delineated by first locating the lowest point, or watershed outlet, on a topographic map. Then, higher elevations can be followed until a
a ridge, or high point, is identified
Three simple rules can be followed when trying to determine watershed boundaries on a map:
- Surface water generally flows at right angles across contour lines on a map.
- Ridges are indicated by the highest elevation contour line in an area.
- Drainages are indicated by contour lines pointing upstream.
Once the boundaries of a watershed have been determined, several watershed parameters can be computed such as
size, maximum and minimum elevations, shape, slope, and drainage patterns.
Surface water flows can also be predicted based on
various potential precipitation events
Hydrologists-
people who study and measure moving water-are also concerned with the aspect and orientation of a watershed.
The aspect of a watershed is the
direction of exposure of sloping lands
orientation is the
general direction of the main portion of a river as it moves down a watershed.
A river with an east-west orientation will probably have slopes that are generally
north-south in aspect
Rain that falls on the land surface within a watershed will immediately move in
one of three general directions
Rain that falls on the land surface within a watershed will immediately move in one of three general directions. First, rain may
evaporate back into the atmosphere.
First, rain may evaporate back into the atmosphere. Second, precipitation may
percolate, or seep, down into the soil and eventually become groundwater
. First, rain may evaporate back into the atmosphere. Second, precipitation may percolate, or seep, down into the soil and eventually become groundwater. Third,
rain may move along the land surface as runoff during and after a storm event.
overland flow
. Runoff water that is moving toward a river or stream
Some overland flow may become stored in
small ponds, wetlands, or lakes before reaching a flowing stream
Overland flow …………….. and …………………… are very dependent on
rates
volumes
precipitation rates, duration of a storm event, and the spatial distribution of precipitation.
A second feature of surface water runoff, called
interflow
interflow, occurs when
precipitation percolates just below the land surface and moves in the same direction as overland flow.
. Interflow moves in
subsurface materials at a slower rate than moving water on the surface and will arrive at a river later than overland flow.
A heavy 45-minute downpour typically generates a
more rapid overland flow than calm, soaking shower over a 48-hour period that generates interflow.
A heavy 45-minute downpour typically generates a more rapid overland flow than calm, soaking shower over a 48-hour period that generates interflow. This variation in surface water runoff is an important reason why
accurate precipitation measurement is so important in water resources management.
Both overland flow and interflow are greatly affected by
human development
Hard surfaces, such as parking lots, roads, and rooftops act as
funnels to drainage pathways
Hard surfaces, such as parking lots, roads, and rooftops act as funnels to drainage pathways that ultimately empty into
rivers, streams, ponds, and lakes.
Impervious barriers created by development also
inhibit interflow and percolation into the soil.
By contrast, forests, cultivated ground, open space, parks, and other vegetated areas are relatively
porous and slow the runoff of precipitation and promote percolation into the soil.
Rivers contain less than
0.01 percent of the Earth’s water but originate in several possible sources
Rivers contain less than 0.01 percent of the Earth’s water but originate in several possible sources. Some are fed by
springs or small streams coming together to create larger rivers of water
Some are fed by springs or small streams coming together to create larger rivers of water. Some originate in
lakes, such as the Mississippi River at Lake Itasca in northern Minnesota
Other rivers, such as the Colorado River in the Rocky Mountains of Colorado, begin as
trickles of melted snow water
A river consists of
of a main channel and all tributaries that flow into it
The beginning of a river is called its
headwaters or source
………………………….. are smaller streams that combine to form larger streams and ultimately rivers
Tributaries
When viewed from above or on an aerial or satellite photo, tributaries often look like
the branches of a tree
The site at which a tributary joins the main river channel is called the
confluence of a river
……………………………… denotes a location toward the headwaters of a river or tributary
Upstream
Upstream denotes a location toward the headwaters of a river or tributary, whereas downstream is
is toward the direction of a confluence with a larger stream, mouth, or other end point of a river.
The imaginary line that connects the deepest points of a river channel is called the
thalweg of a river
Overland flow and interflow are
important sources of water for many rivers
After a rainstorm, water levels in rivers often
rise
. After a rainstorm, water levels in rivers often rise and cause
some water to percolate into the banks (sides) of a river
. After a rainstorm, water levels in rivers often rise and cause some water to percolate into the banks (sides) of a river (called………………)
bank storage
). As local conditions become drier, this bank storage will
slowly move back into the river as flow decreases.
Porous riverbanks allow significant amounts of storm runoff to be
temporarily held as bank storage and can reduce the threat of flooding downstream.
The zone beneath a river is called the
hyporheic
The zone beneath a river is called the hyporheic (from the Greek meaning “…………………………………….”) zone
to flow beneath
The zone beneath a river is called the hyporheic (from the Greek meaning “to flow beneath”) zone and varies in
depth depending on the composition and size of a river bottom
The hyporheic zone can extend
beneath a riverbed to a depth of a few inches (less than 10 cm) or down to several feet (1 m or more).
Oxygen is the limiting factor that determines
what type of organisms can survive in this area
). Oxygen is the limiting factor that determines what type of organisms can survive in this area, with the ………………. waters of …………………… altitudes supporting the most life.
colder
high
Geomorphology is the study of
forces that shape the surface of the Earth
Geomorphology is the study of forces that shape the surface of the Earth. The greatest force in the
the alteration of land is moving water, and its effects can easily be seen along rivers.
. Rivers develop many features after
years of traveling the same course.
A “young” river has a …….. valley
V-shaped
A “young” river has a V-shaped valley, with some rivers having
almost vertical walls and swift-flowing water
As a river continues toward its mouth and seeks a base level, the slope of the river channel generally
decreases
As a river continues toward its mouth and seeks a base level, the slope of the river channel generally decreases. Eventually, the river valley
widens and becomes more U-shaped where silt and sand have created a wide plain caused by previous floods.
Playfair’s Law
Every river appears to consist of a main trunk, fed from a variety of branches, each running in a valley proportional to its size, and all of them together forming a system of valleys connecting with one another
