chapter 4 Flashcards
Overland flow definition
the flow of water that occurs when excess storm-water, melt-water, or other sources flows over the earth’s surface.
overland flow might occur becauses
- either soil is saturated to full capacity,
- rain arrives more quickly than soil can absorb it,
- or impervious areas (roofs, pavement and cities concrete) send their runoff to surrounding soil that cannot absorb all of it.
overland flow cause
soil erosion by water.
overland flow is also called ………………………… and it means…………………..
a nonpoint source
runoff that occurs on the ground surface before reaching a channel
nonpoint source pollution means
If a nonpoint source contains man-made contaminants, or natural forms of pollution (such as rotting leaves) the runoff
drainage basin means
A land area which produces runoff that drains to a common point
surface runoff in urban areas cause
of urban flooding which can result in property damage, damp and mold in basements, and street flooding.
how is surface runoff generated?
- either by rainfall
- snowfall
- by the melting of snow, or glaciers.
Typically snowmelt will peak in the
spring
glacier melt in the
summer
Typically snowmelt will peak in the spring and glacier melt in the summer, leading to
pronounced flow maxima in rivers affected by them.
The determining factor of the rate of melting of snow or glaciers is
- air temperature
- the duration of sunlight.
high mountain regions, ……………………..frequently ……………on sunny days and …………………………….. for this reason.
streams
rise
fall on cloudy ones
In areas where there is no snow, runoff will come from
rainfall
Infiltration excess overland flow occur when
the rate of rainfall on a surface exceeds the rate at which water can infiltrate the ground, and any depression storage has already been filled.
flooding excess overland flow more commonly occurs in
arid and semi-arid regions
Infiltration excess overland flow where……………………………………….. and ………………………………………………..because of…………………………………………., or in …………………………areas.
rainfall intensities are high
the soil infiltration capacity is reduced
surface sealing
paved
where rainfall intensities are high and the soil infiltration capacity is reduced because of surface sealing, or in paved areas. This occurs largely in
city areas where pavements prevent water from flooding.
saturation excess overland occur when
When the soil is saturated and the depression storage filled, and rain continues to fall, the rainfall will immediately produce surface runoff.
saturation excess overland flow is also called
saturated overland flow
Antecedent soil moisture
Soil retains a degree of moisture after a rainfall
Antecedent soil moisture affect
residual water moisture affects the soil’s infiltration capacity.
During the next rainfall event, the infiltration capacity will cause
the soil to be saturated at a different rate
The higher the level of antecedent soil moisture, the………………….
the more quickly the soil becomes saturated
The higher the level of antecedent soil moisture, the more quickly the soil becomes saturated. Once the soil is saturated ……………………………….. occurs
runoff
subsurface return flow
After water infiltrates the soil on an up-slope portion of a hill, the water may flow laterally through the soil, and exfiltrate (flow out of the soil) closer to a channel.
subsurface return flow is also called
through flow
hydraulics is a derivative of the Greek words
hydro (meaning water) and aulis (meaning tube or pipe)
Originally, the science of hydraulics covered the
physical behavior of water at rest and in motion
the term hydraulics has broadened its meaning to include the ………………………..
physical behavior of all liquids
the physical behavior of all liquids includes
power hydraulics
power hydraulics
confined liquids are used under controlled pressure to do work
Although the modern development of hydraulics is comparatively recent, the ancient cultures were familiar with many hydraulic principles and applications. They ………………………………………
conveyed water along channels for irrigation and domestic purposes, using dams and sluice gates to control the flow
…………………..discovered the fundamental law underlying the entire science of hydraulics
Pascal
Pascal’s theorem was as follows:
If a vessel full of water, and closed on all sides, has two openings, one a hundred times as large as each other, and if each is supplied with a piston that fits exactly, then a man pushing the small piston will exert a force that will equal that of one hundred men pushing the large piston and will overcome that of ninety-nine men.
Factors Affecting Hydraulic systems
- pressure
- fluid flow
- Volume and velocity of flow
Pressure may be exerted in
one direction, several directions, or in all directions
A solid exerts pressure
downward
liquid will exert pressure
on all the surfaces with which it comes in contact
Gases will exert pressure
in all directions because it completely fills the container
Pascal discovered that pressure set up in a fluid
acts equally in all directions
Pascal discovered that pressure set up in a fluid acts equally in all directions. Another way to state this is that
a force applied on any area of an enclosed liquid is transmitted equally and undiminished to all areas throughout the enclosure. Thus, if a number of passages exist in a system, pressure can be distributed through all of them by means of a liquid.
pressure is
transmitted
To understand power hydraulic systems in action, it is necessary to become familiar with the
elementary characteristics of fluids in motion.
volume rate of flow
The quantity of fluid that passes a given point in a system in a unit of time
method of expressing volume rate of flow in hydraulic systems
Gallons per minute
Velocity of flow
the rate or speed at which the fluid moves forward at a particular point in the system
Velocity of flow is expressed in
feet per second
…………………………………… and ………………………..are often considered together
Volume and velocity of flow
With the volume of input unchanged, the velocity of flow …………………………as the cross-section or size of the pipe decreases
increases
the velocity of flow decreases as the area …………………………….
increases
In a stream, velocity of flow is slow at …………………….parts of the stream and rapid at ………………………….parts even though the volume of water passing each part is the …………………………..
wide
narrow
same
what do you conclude from the following
as volume decreases speed increases
Streamflow is also called
channel runoff
Streamflow definition
the flow of water in streams, rivers, and other channels, and is a major element of the water cycle
streamflow is one component of …………………………………………………………………………………………………………………….. the other component being…………………………………
the runoff of water from the land to water-bodies, the other component being surface runoff.
Water flowing in channels comes from
surface runoff from adjacent hill-slopes, from groundwater flow out of the ground, and from water discharged from pipes.
The discharge of water flowing in a channel is measured using
stream gauges or can be estimated by the Manning equation
hygrograph
The record of flow over time
The record of flow over time
hydrograph
Flooding occurs when
the volume of water exceeds the capacity of the channel
…………………….and ……………………..play a critical role in the hydrologic cycle that is essential for all life on Earth.
Streams and rivers
A diversity of biological species, from unicellular organisms to vertebrates, depend on
flowing-water systems for their habitat and food resources.
Rivers are major aquatic landscapes for
all manners of plants and animals
Rivers even help keep the aquifers underground …….
full of water by discharging water downward through their streambeds
full of water by discharging water downward through their streambeds. In addition to that the oceans ……………………………………………… because ………………………………………………………….
stay full of water because rivers and runoff continually refreshes them.
Streamflow is the main mechanism by which
water moves from the land to the oceans or to basins of interior drainage
Source of streamflow
- channel precipitation
- ground water
- Interflow
- Overland flow
Mechanisms that cause changes in streamflow
- Natural mechanism
- human-induced machanisms
Mechanisms that cause changes in streamflow:
Natural mechanisms:
- Runoff from rainfall and snowmelt
- Evaporation from soil and surface-water bodies
- Transpiration by vegetation
- Ground-water discharge from aquifers
- Ground-water recharge from surface-water bodies
- Sedimentation of lakes and wetlands
- Formation or dissipation of glaciers, snowfields, and permafrost
Mechanisms that cause changes in streamflow:
Human-induced mechanisms:
- Surface-water withdrawals and transbasin diversions
- River-flow regulation for hydropower and navigation
- Construction,removal, and sedimentation of reservoirs and stormwater detention ponds
- Stream channelization and levee construction
- Drainage or restoration of wetlands
- Land-use changes such as urbanization that alter rates of erosion, infiltration, overland flow, or evapotranspiration
- Wastewater outfalls
- Irrigation wastewater return flow
Streamflow is measured as an:
an amount of water passing through a specific point over time.
Runoff of water in channels is responsible for transport of
sediment, nutrients, and pollution downstream.
Without streamflow, the water in a given watershed
would not be able to naturally progress to its final destination in a lake or ocean
Runoff of water in channels is responsible for transport of sediment, nutrients, and pollution downstream. Without streamflow, the water in a given watershed would not be able to naturally progress to its final destination in a lake or ocean. This would
disrupt the ecosystem
Streamflow is one important route of water from …………………… to …………………………… and…………………………
the land to lakes and oceans
Streamflow is one important route of water from the land to lakes and oceans. The other main routes are
- surface runoff (the flow of water from the land into nearby watercourses that occurs during precipitation and as a result of irrigation),
- flow of groundwater into surface waters, and the
- flow of water from constructed pipes and channels.
Streamflow confers on society both ……………………… and …………………….
benefits and hazards
Runoff downstream is a means to collect water for ………………………….. for………………………….
storage in dams for power generation of water abstraction.
The flow of water assists transport ……………………………….
downstream
A given watercourse has a maximum streamflow rate that can be accommodated by …………………………
the channel
Streamflow confers on society both benefits and hazards. Runoff downstream is a means to
- collect water for storage in dams
- for power generation of water abstraction.
- The flow of water assists transport downstream.
show how pressure is exerted
