lecture notes part 2 Flashcards
to measure water rate and volume there is a need to measure
- depth of water
- terrain
- velocity
type of water measurement
- overland flow
- river discharge
- water storage in lakes and reservoir
overland flow
surface water runoff that is moving within a watershed toward a river
overland flow has usually a …………….. distance
short
overland flow is calculated by
Q=kiA
overland flow is calculated by
Q = KiA
where k =
runoff coefficient
overland flow is calculated by
Q = KiA
where i =
rainfall intensity (cm/hr)
overland flow is calculated by
Q = KiA
where A =
area of watershed in hectars
overland flow is calculated by
Q = KiA
where Q =
peak rate of runoff in m3/s
Q=KiA
this formula is used to
design storm drains and culverts and other structures that control runoff, primarily in urban areas
K is max in
downtown (0.7 - 0.95)
k is min in
parks (0.1 - 0.25)
river discharge is
the amount of water carried in a river at any time
river discharge
is the amount of water carried in a river at any time, which is the
volume of water m3
river discharge:
is the amount of water carried in a river at anytime, which is the volume of water m3 flowing past
a given point during a given period of time
river discharge is measured by ……………….. or ……………………
m3/s or L/min
river discharge varies from …………………………. in small streams
0.06 m3/s
river discharge varies from 0.06 m^3 /s in small streams to ………………………. in mississippi river
42,000 - 339,000 m3/s
the highest record was 1.5 x 106 m3/s in the
amazon river of brazil
calculations of river discharge?
- measure of the depth of river at a particular cross section
- water velocity is measured in several points and depths along the same cross section
- use these data in the equation Q=AV
Q=AV
where Q =
discharge average
Q=AV
where A =
cross section area of a channel
Q=AV
where V =
average water velocity
rivers which have continiously changing riverbeds ( that are consistency of ……………………)
sand and gravel
rivers which have continiously changing riverbeds ( that are consistency of sand and gravel), the measurements are made
weekly to provide more accurate data on the size and shape of the channel bottom
factors affecting river discharge?
- rock and soil type
- land use
- rainfall
- relief
- weather conditions
6.
rock and soil type
sand
absorb water easily so runoff is rare
rock and soil type
clay
clay because they are closely packed water reaches the river more quickly
rock and soil type
limestone
allow water to pass through porous rocks
land use:
in urban city roads
water runs into drains
land use
in rural areas
ploughing up and down allows water to drain and reach rivers
land use:
deforestation
allows rainfall to reach the ground faster and runs as drains
rainfall
…………………………………… will affect a river discharge
the amount and type of rainfall
. rainfall
antecedent rainfall saturated the ground further rainfall will
run as a runoff towards the river
rainfall
heavy continual rain or melting snow means
more water flowing into the river
relief
steep slopes causes rainfall to
run over the surface before it can infiltrate
weather conditions:
hot dry weather can
bake the soil, so rainfall cant soak in. it move above the surface into the river
- weather conditions:
hot dry weather can bake the soil, so rainfall cant soak in. it move above the surface into the river
high temperature increases
evaporation from water surfaces and reduce discharge
- weather conditions:
hot dry weather can bake the soil, so rainfall cant soak in. it move above the surface into the river
high temperature increases evaporation from water surfaces and reduce discharge
very cold weather lead to
frozen ground so water cant soak in
average velocity measurements:
the water velocity varies according to
the depth and nearness to obstacles
average velocity measurements:
the water velocity varies according to the depth and nearness to obstacles such as
bed, bancks
average velocity measurements:
the water velocity varies according to the depth and nearness to obstacles such as bed, bancks. Which generate
friction and drag
average velocity measurements:
the water velocity varies according to the depth and nearness to obstacles such as bed, bancks. Which generate friction and drag. The velocity is max at
the surface
average velocity measurements:
the water velocity varies according to the depth and nearness to obstacles such as bed, bancks. Which generate friction and drag. The velocity is max at the surface and zero at
bed
a good estimate of the average velocity is by
multiplying the surface velocity by 0.8
agencies around the world collect river discharge data. In USA, it is US geologic survey (USGS) that is responsible for
river flow data
agencies around the worls collect river discharge data. In USA, it is US geologic survey (USGS) that is responsible for river flow data.
Real – time data are recorded at
15 – 60 min interval
agencies around the worls collect river discharge data. In USA, it is US geologic survey (USGS) that is responsible for river flow data.
Real – time data are recorded at 15 – 60 min interval but may be more frequent during
critical events
Water velocity is measured by a
flow melt
Water velocity is measured by a flow melt. A flow meter turns a small propeller at the
end of a shaft on the meter
Water velocity is measured by a flow melt. A flow meter turns a small propeller at the end of a shaft on the meter. Propeller rotations are
electronically recorded over a set period of time
Water velocity is measured by a flow melt. A flow meter turns a small propeller at the end of a shaft on the meter. Propeller rotations are electronically recorded over a set period of time and allow a …………………………. to calculate average water velocity
hydrographer
Since water velocity in rivers often pulsates, observations are made in interval of
40 - 70 seconds
Since water velocity in rivers often pulsates, observations are made in interval of 40-70 seconds.
Measurement are made by
dividing a river into cross sectional segments of not greater than 10% of the total river width
Measurement are made by dividing a river into cross sectional segments of not greater than 10% of the total river width. Therefore, …………….. vertical section measurements are typical
10-20
Water velocity ofter varies from ……………………….. at the bottom to …………………………. at the surface
almost zero at the bottom to near maximum at the surface
The average of the velocities at …………………………. depth provides the average velocities for a given vertical section
20% and 80%
The stage of river or lake stage is the
height of the water surface above a set reference elevation
If the streambed is known and the water surface stage is subtracted, the result is
the depth of water in the river
If the streambed is known and the water surface stage is subtracted, the result is the depth of water in the river.
For this purpose a …………………………… is used
staff gauge
Staff gauge is a
metal ruler attached to a permanent fixture
The elevation of water on the staff gauge is called
gauge height
Discharge is sometimes determined by using
the river stage directly
Discharge is sometimes determined by using the river stage directly. In this case the result is a
rating curve
Discharge is sometimes determined by using the river stage directly. In this case the result is a rating curve
Such curve is generated by making discharge measurements during
various times of the year, usually months
Such curve is generated by making discharge measurements during various times of the year, usually months, and plotting these against
gauge height
Such curve is generated by making discharge measurements during various times of the year, usually months, and plotting these against gauge height. Once constructed, a rating curve eliminates the need
of velocity and depth measurements unless the channels cross section changes
A river hydrograph is
a graph of discharge over time and can be plotted daily, weekly, monthly or annually
Seasonal variations are evident
on an annual hydrograph
Seasonal variations are evident on an annual hydrograph, whereas flood events are displayed on
hourly, daily or weekly hydrographs
A recorder is a device used to
record the elevation of water flowing through an open channel or river over time
A recorder is a device used to record the elevation of water flowing through an open channel or river over time
A recorder is usually located in
a riverbank
Historically, water measurements have ben used in Egypt 5000 years ago by a
nilometer
Nilometers were used to measure
the nile river
Historically, water measurements have ben used in Egypt 5000 years ago by a nilometer. Nilometers were used to measure the nile river. High river stage meant the
deposition of more sediment on floodplains for crops, while low- level stage meant shortage in irrigation and poor crops
Pharaohs placed nilometers
upstream (further) south to provide an early warning system of future water discharge
