Post on 02-Nov-2014
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MAIN HYDROLOGICAL MAIN HYDROLOGICAL CONCEPTSCONCEPTS
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To assist the students to develop and enhance the ability and knowledge in
main hydrological concepts such as
1. hydrological cycle2. water balance equation
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At the end of the course, students should be able to:
• Define hydrology.• Apply fundamental knowledge of
hydrology particularly use in civil and environmental engineering.
• Apply water balance equation as the base of a modeling of hydrology which covers processes of precipitation, evaporation, infiltration, runoff and groundwater.
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HydrologyHydrology
• is a multidisciplinary subject that deals with the occurrence, circulation, storage, and distribution of surface and ground water on the earth.
• The domain of hydrology includes the physical, chemical, and biological reactions of water in natural and man-made environments.
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Hydrology is…. • a science that studies the
availability and movement of water in the earth.
• also defined as a science related to the occurrence and distribution of natural water on the earth.
• hydrology covers many type of water, including transformation among liquid, solid and gas in atmosphere, surface and subsurface land.
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To civil and environmental engineers, hydrogeologists, and other earth scientists because of the environmental significance of
water supply, major floods droughts drainage and urban stormwater
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Hydrologic cycle Hydrologic cycle is a continuous process in which water is evaporated from water surfaces and oceans, moves inland as moist air masses, and produce precipitation if the correct vertical lifting conditions exist. The precipitation that falls from clouds onto the land surface of the earth is dispersed to the hydrologic cycle via several pathways (Fig.1-1).
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impermeable layer
Evaporationfrom Lake/river
Evaporationfrom Land
Evaporationfrom Ocean
Transpiration
Run-offInfiltration
Groundwater Flow
Precipitation
Wind
Figure 1-1: Hydrology Cycle
Cloud
Cloud Cloud
Precipitation Precipitation
Run-off
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P = PrecipitationT = Transpiration I = InfiltrationR = RunoffG = Groundwater flow E = Evaporation from lake, land surface and oceanET = EvapotranspirationLS = Land surfaceWT = Water table
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Main River
River
River
River
River
Catchment boundary
Lake
Spring
Spring
Spring
HIGHLAND
AREA
COASTAL
AREA
Sketch of Movement of Water on the Land Surface
A watershed is a contiguous (sharing a boundary) area that drains to an outlet, such that precipitation that falls within the watershed runs off through that single outlet.
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Outlet
Outleta. Elongated shape b. Concentrated shape
Figure 1-2Typical watershed areas
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Water Balance Equation
In quantitative terms, hydrology cycle can be represented by a closed equation which represents the principle of conservation of mass. And many forms of this expression, called the water balance.
Water balance equation is the base of a modelling of hydrology.
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Location Area of Water
km2
Volumeof Water
km3
Percentage
Total of Water
(%)
Surface Water- Fresh Water in Lake- Salt Water in Lake- Fresh Water in River &
Stream
Subsurface Water- Groundwater, upper
800m depth- Groundwater, below
800m depth
Soil Moisture
Ice and Glacier
Atmosphere
Ocean
854,330.73698,997.87
129,444,050.00
129,444,050.00
129,444,050.00
17,863,278.90
510,009,557.00
361,148,899.50
124,965.285104,137.7381,249.652
4,165,509.5294,165,509.529
66,648.152
29,158,566.703
12,913.080
1,320,466,520.000
0.0090.0080.001
0.310.31
0.005
2.15
0.001
97.20
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Volume of water in the world 1,358 million km3.
Volume of fresh water 2.8 %, most of fresh water are in the form of ice and glacier
Fresh water of groundwater, lake, cloud and rain 8.54 million km3 or only 0.63%.
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dtdS
Q I
where: I = inflow [L3/t]
Q = outflow [L3/t]dS/dt = change in storage per time [L3/t]
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The same concept can be applied to small basins or large watersheds
P – R – G – E – T = ΔS where:
P = precipitation, R = surface runoff, G = groundwater flow,
E = evaporation, T = transpiration,ΔS = change in storage in a specified time
period.
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For a given month, a 121 ha lake has 0.43 m3/s of inflow, 0.37 m3/s of outflow, and total storage increase of 1.97 ha-m. A USGS gage next to the lake recorded a total of 3.3 cm precipitation for the lake for the month. Assuming that infiltration loss is insignificant for the lake, determine the evaporation loss, in cm, over the lake for the month.
Solution: Solving the water balance for inflow I and outflow Q in a lake gives,
for evaporation, E = I – O + P – ΔS,
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1ha10,000m
121ha
1hour3,600sec
1day24hr
1month30day
1monthsecm
0.43
2
3
I
1ha10,000m
121ha
1hour3,600sec
1day24hr
1month30day
1monthsecm
0.37
2
3
O
= 0.92 m = 92 cm
= 0.79 m = 79 cm
P = 3.3 cm
121ha
m1.97haΔS
= 0.0163 m = 1.63 cm
E = 92 – 79 + 3.3 – 1.63 = 14.67 cm
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A swimming pool (6m 6m 1.5m) has a small leak at the bottom. Measurements of rainfall, evaporation, and water level are taken daily for 10 days to determine what should be done for repair. Estimate the average daily leakage out of the swimming pool in cm3/day. Assume the pool is exactly 1.5 m deep at the end of day 1.
Day Evaporation
(mm)
Rainfall(mm)
Measured Level(mm)
12345678910
12.70
12.70
12.712.7
012.712.712.7
-25.4
-50.8
--
101.6---
1,524
1,321
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Solution
The water balance equation becomes: O = P – E – ΔSTotal change in storage, S = 1,321 – 1,524 = -203 mmTotal precipitation, P = 25.4 + 50.8 + 101.6 = 177.8 mmEvaporation, E = (7) (12.7) = 88.9 mm
Thus, outflow,O = 177.8 – 88.9 – (-203) = 291.9 mm
Outflow should be in cm3/day. The height change is distributed over the pool area. Q =
10days1m
100cm6m
1m100cm
6m10mm1cm
291.9mm
Q = 1,050,840 cm3/day
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Fundamental to analyses, forecasting, and modeling.
Hydrologic data consists of; Wind Temperature Humidity Evaporation Precipitation Solar radiation
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Hydrology is the science of water.
It embraces the occurrence, distribution, movement and properties of the waters of the earth.
A mathematical accounting system may be constructed for the inputs, outputs and water storages of a region so that a history of water movement over time can be estimated.
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