Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
-
Upload
roger-shedden -
Category
Documents
-
view
213 -
download
0
Transcript of Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
1/50
Module
The Hydrologic Cycle
and
Rainfall Runoff Processes
Ir Dr Kelvin Kuok
Faculty of Engineering, Computing & Science
Room E613
CVE 30001 – Urban Water Resource
2016
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
2/50
Hydrology
Applied Hydrology Hydrologic cycle
Hydrology Component
Effect of urbanisation
All about water Inventory of water
Global Distribution
Renewal
Rainfall Runoff Process
Rainfall Intensity
Rainfall intensity calculation methods
Outline
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
3/50
What is Engineering Hydrology?
Hydrology is the science of water.
It is the study of the
occurrence
character
movement
of water within and between the physical and biological
components of the environment.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
4/50
Applied Hydrology
The practical application of hydrology
Provide guidance for planning and management of water resource.
Found in such tasks as
Design and operation of hydraulic structures
Water supply
Wastewater treatment and disposal
Irrigation
Drainage
Hydropower generation
Flood control etc
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
5/50
Hydraulics Structure
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
6/50
Dam (water supply & hydroelectric)
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
7/50
Irrigation
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
8/50
Hydrological Cycle
An orderly scheme to systematically examine and analyze the
movement of water through the landscape
The hydrologic cycle is the central focus of hydrology.
The cycle has no beginning or end.
Its processes occur continuously
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
9/50
Hydrologic cycle
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
10/50
Evaporation-moisture passes into atmosphere as vapor.
Surface runoff – runoff travels over the soil surface to the
nearest stream channel.
Percolation – passage of water under hydrostatic pressure
through intersectics of a soil and rock.
Infiltration- passage of water through surface of soil.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
11/50
Hydrologic Cycle - Animation
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
12/50
Evaporation
The conversion of water from a liquid into a gas
Water is transferred from the surface to the atmosphere through
evaporation, the process by which water changes from a liquid to a gas.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
13/50
Precipitation
Precipitation is the primarymechanism for transporting waterfrom the atmosphere to the surface
of the earth. There are several formsof precipitation, the most commonof which is rain. Other forms of
precipitation include; hail, snow,sleet, and freezing rain. A well
developed extra-tropical cyclone could be responsible for thegeneration of any or all of theseforms of precipitation.
Transfer of water from the atmosphere back to earth
http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/rain_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/hail_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/snow_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/sleet_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/freeze_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/cyclone.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/cyclone.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/freeze_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/sleet_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/snow_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/hail_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/rain_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
14/50
Hail – frozen form of precipitation, associated with
thunderstorm.
Sleet – wintry precipitation, snows partially melted on its
way to ground.
Tropical cyclone: a storm system characterized by a large
low pressure centre and numerous thunderstorms that
produced strong winds and heavy winds.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
15/50
Transpiration
Transfer of water from plants to the atmosphere
Transpiration is theevaporation of water intothe atmosphere from theleaves and stems of plants.
Transpiration accounts forapproximately 10% of allevaporating water.
http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/evaporation.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/evaporation.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
16/50
Groundwater
Water that has penetrated the earth's surface
Groundwater is all the water that haspenetrated the earth's surface and isfound in one of two soil layers. The onenearest the surface is the "zone ofaeration", where gaps between soil are
filled with both air and water. Belowthis layer is the "zone of saturation",where the gaps are filled with water.
The water table is the boundarybetween these two layers. As the
amount of groundwater water
increases or decreases, the water tablerises or falls accordingly. When the
entire area below the ground issaturated, flooding occurs because allsubsequent precipitation is forced toremain on the surface.
http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/1997_flood.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/1997_flood.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
17/50
Runoff
Transfer of landwater to the oceans
Runoff is the movement oflandwater to the oceans, chiefly inthe form of rivers, lakes, andstreams. Runoff consists of
precipitation that neither evaporates,transpires nor penetrates thesurface to become groundwater.Even the smallest streams areconnected to larger rivers that carry
billions of gallons of water intooceans worldwide.
http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/precip_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/evaporation.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/transpiration.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/groundwater.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/groundwater.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/transpiration.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/evaporation.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/precip_hyd.rxml?hret=/guides/mtr/hyd/smry.rxml&prv=1
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
18/50
Hydrology Component
Precipitation Evaporation
Interception
Transpiration
Overland Flow Surface Runoff Runoff to Streams
and Ocean
Infiltration Subsurface Flow
Groundwater
RechargeGroundwater Flow
A t m o s p h e r i c W a t e r
S u b s u r f a c e W a t e r
S u r f a c e W a t e r
+
+
+
+
+
+
+
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
19/50
Infiltration
Evaporation
Runoff
Rainfall
HydrologicData
Rainfall-Runoff Model
-Double Mass Curve Analysis-Arial Rainfall
-Runoff
-Flow Duration Curve
-Hydrograph/UnitHydrograph
-Infiltration Analysis
Evapotranspiration
-Evaporation Analysis
Hydrologic Component
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
20/50
System Concept
Precipitation, I(t)
Streamflow, Q(t)
System BoundaryWatershed Surface
Watershed Divide
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
21/50
Process(Basin)
Input
(Rainfall)
Output
(Runoff)
Simple Hydrologic System Model
Unsteady Flow Equation ; I-Q=dS/dt
I = Input (volume/time)O= Output (volume/time)
dS/dt = Time rate of change of storage
Basic Equation of Hydrologic Cycle
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
22/50
All about Water
Approximately 97% of all the water on the Earth is in the oceans.
The other 3% is held as freshwater in glaciers and icecaps,groundwater, lakes, soil, the atmosphere, and within life.
The oceans supply most of the evaporated water found in theatmosphere.
Only 91% of it is returned to the ocean basins by way of precipitation
The remaining 9% is transported to areas over landmasses whereclimatological factors induce the formation of precipitation. Theresulting imbalance between rates of evaporation and precipitation
over land and ocean is corrected by runoff and groundwater flow tothe oceans.
Water is continually cycled between its various reservoirs.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
23/50
Inventory of water at the earth’s surface
Reservoir Volume (cubic kmx 1,000,000) Percent of Total
Oceans 1370 97.25
Ice Caps and Glaciers 29 2.05
Groundwater 9.5 0.68
Lakes 0.125 0.01
Soil Moisture 0.065 0.005
Atmosphere 0.013 0.001
Streams and Rivers 0.0017 0.0001
Biosphere 0.0006 0.00004
Source: Pidwirny, M. (2006)
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
24/50
Global Distribution of Water
60% of river water in Amazon and Congo
about 8% of Canada is lake (largest area of lake in the
world)
global precipitable water vapour = 25 mm; global average
annual ppt. = 1000 mm, therefore, atmospheric water is
completely recycled 40X per year or every 9 days
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
25/50
Renewal of Water
On average water is renewed in rivers once every 16 days
Water in the atmosphere is completely replaced once every 8
days
Slower rates of replacement occur in large lakes, glaciers, ocean
bodies and groundwaterSome of these resources (especially groundwater) are being used
by humans at rates that far exceed their renewal times. This type
of resource use is making this type of water effectively
nonrenewable
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
26/50
Typical residence times of water found in various reservoirs
Table 8b-2:.Reservoir Average Residence Time
Glaciers 20 to 100 years
Seasonal Snow Cover 2 to 6 months
Soil Moisture 1 to 2 months
Groundwater: Shallow 100 to 200 years
Groundwater: Deep 10,000 years
Lakes 50 to 100 years
Rivers 2 to 6 months
Source: Pidwirny, M. (2006)
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
27/50
Effect of urbanisation to Hydrologic Cycle
Change in Land Use
Eg: Tree removals, Building ofhouses, Filling in of farm ponds,
Building of roads, Diverting
streams to supply water for
people, Discharging of sewage
into streams, Building of industrialbuildings etc
Effect on water system
More storm runoff and erosion
More sediment is washed into streams
Flooding can occur as water-drainage
patterns are changed
Harms the water quality of the streams
Increased sewage in streams causes
pollution -- it can kill fish and make
water unusable for other purposes
downstream
More pavement means less water will
soak into the ground, hence the
underground water table will have less
water to recharge it. Thus will lower the
water table
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
28/50
Fixing the Problem
Change in Land Use
Improvements in the storm
drainage system
Wells are drilled to recharge
underground aquifers
Reuse wastewater
Ecological-designed recharge
ponds disperse some storm
drainage to artificially recharge
shallow aquifers
Effect on Water System
New storm-drainage systems
reduce flooding during storms.
Water is actually injected into
recharge wells to put water back
into underground aquifers Reusing wastewater means less
pollution, more water
conservation, and additional water
for recharging aquifers
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
29/50
Average Annual Precipitation
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
30/50
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
31/50
Relationship between rainfall, infilt ration and runoff
Water reaching the ground surface infiltrates into the soil until it
reaches a stage where the rate of rainfall (intensity) exceeds theinfiltration capacity of the soil.
Thereafter, surface puddles, ditches, and other depressions are filled(depression storage), after which runoff is generated.
Source: L ins ley et al. 1958
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
32/50
The infiltration capacity of the soil depends on
texture and structure and soil moisture content. The
initial capacity (of a dry soil) is high but, as the storm
continues, it decreases until it reaches a steady value
termed as final infiltration rate
The process of runoff generation continues as long as the
rainfall intensity exceeds the actual infiltration capacity of
the soil but it stops as soon as the rate of rainfall dropsbelow the actual rate of infiltration.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
33/50
Physical characteristics affecting runoff
Soil type
The infiltration capacity is dependent on the porosity of a soilwhich determines the water storage capacity and affects theresistance of water to flow into deeper layers.
The highest infiltration capacities are observed in loose, sandy
soils while heavy clay or loamy soils have considerable smallerinfiltration capacities.
The infiltration capacity depends on the moisture contentprevailing in a soil at the onset of a rainstorm.
The initial high capacity decreases with time (provided the raindoes not stop) until it reaches a constant value as the soil profilebecomes saturated
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
34/50
Physical characteristics - Soil Type
Clay Sand
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
35/50
Physical characteristics - Vegetation
The amount of rain lost to interception storage on the foliagedepends on the kind of vegetation and its growth stage.
A dense vegetation cover shields the soil from the raindropimpact and reduces the crusting effect as described earlier.
The root system as well as organic matter in the soil increase thesoil porosity thus allowing more water to infiltrate.
Vegetation also retards the surface flow particularly on gentleslopes, giving the water more time to infiltrate and to evaporate.
An area densely covered with vegetation, yields less runoff thanbare ground.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
36/50
Physical characteristics -Vegetation
Exposed Soil
Road/pavement Forest
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
37/50
Physical characteristics - Slope & Catchment Size
Steep slope plots yield more runoff than those with gentle slopes.
Quantity of runoff decreased with increasing slope length.
Mainly due to lower flow velocities and subsequently a longer
time of concentration This means that the water is exposed for a
longer duration to infiltration and evaporation before it reaches
the measuring point.
The runoff efficiency (volume of runoff per unit of area) increases
with the decreasing size of the catchment i.e. the larger the size
of the catchment the larger the time of concentration and the
smaller the runoff efficiency.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
38/50
Meteorological factors affecting runoff
• Type of precipitation (rain, snow, sleet, etc.)
• Rainfall intensity• Rainfall amount
• Rainfall duration
• Distribution of rainfall over the watersheds
• Direction of storm movement
• Antecedent precipitation and resulting soil moisture
• Other meteorological and climatic conditions that affect
evapotranspiration, such as temperature, wind, relativehumidity, and season.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
39/50
Rainfall Intensity
The most common historical rainfall data are daily total
amounts at selected locations
obtained from a "standard raingauge" (tube) which gives the
depth of rainfall accumulated between observations.
Traditional Rain Gauge Optical Rain Gauge Wireless Rain Gauge
http://images.google.com/imgres?imgurl=http://www.chilbolton.rl.ac.uk/weather/images/Optical%2520Rain%2520Gauge.jpg&imgrefurl=http://www.chilbolton.rl.ac.uk/weather/raingaugedetails.htm&h=534&w=416&sz=45&hl=en&start=48&sig2=w4N_YLVAmVCWL-33qFtmbQ&um=1&tbnid=viHLglp8yPPmLM:&tbnh=132&tbnw=103&ei=SXCRSPGJO4Ko6wO-vuWdBw&prev=/images%3Fq%3Drain%2Bgauge%26start%3D40%26ndsp%3D20%26um%3D1%26hl%3Den%26rlz%3D1T4SKPB_enMY274MY274%26sa%3DNhttp://www.compleatnaturalist.com/images/Prof%20Rain%20Gauge.jpg
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
40/50
Rainfall Intensity Calculation Methods
Arithmetic Mean Method
Thiessen Method
Isohyetal Method
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
41/50
Arithmetic Mean
Simplest method
Averaging rainfall depth across a number of gauges
Uniformly distributed
Does not vary greatly
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
42/50
Isohyetal method
Locate all rainfall stations on
a base map and record the
rainfall amount.Draw isohyets (lines of equal
rainfall) by proportioning the
distances between adjacent
gauges according todifferences in catch.
The most basic method of representing the spatial distribution.
This is generally the most accurate method but is also the mostlaborious.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
43/50
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
44/50
Isohyetal method Cont.
• Then calculate the mean precipitation for the area
corresponding to each isohyet (Contour).
• Calculate the fraction of catchment area under each isohyet,
multiply by the mean precipitation for that area and sum to
get the catchment average.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
45/50
Thiessen method
Locate all rainfall stations on a
base map and record the rainfall
amount.
Connect each station bystraight lines with the several
nearest stations to form a series
of triangles.
Erect perpendicular bisectors
on each of these lines andextend them to the intersect with
other bisectors, thus forming a
series of irregular polygons
This involves determining the area of influence for each station,
rather than assuming a straight-line variation. It is easier thanthe isohyetal method but less accurate
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
46/50
Thiessen method cont.
Measure the fraction of the catchment area in each polygon (called
the Thiessen constant), multiply by the rainfall catch at the stationwithin the polygon and sum to get the catchment average.
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
47/50
Exercise
Area of Basin = 32.7 km2
SationNumber Station Precipi tation(mm)
1 20
2 26
3 25
4 32
5 35
6 38
7 40
8 509 52
10 48
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
48/50
Exercise Hints when finding Area
The scale of basin map is 1:50,000
Make the scale of the grid paper 1:50,000
Meaning every cm on the grid paper represents 50,000cm on the
ground or 0.5km
Count up all the large blocks first, then the small blocks (find outhow many blocks in each big block)
Multiply by the number of km2 that each large block represents
Area should be not too far from the given area (which is 32.7km2)
Solution to exercise
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
49/50
So ut o to e e c se
Sation
Number Station Precip (mm) [A]
Area of
polygon
(km2)
Fractional
Area [B]
Area weighted
precipitation
(A*B)
1 20 0.67 2.06 0.41
2 26 1.60 4.89 1.27
3 25 2.97 9.10 2.28
4 32 1.95 5.97 1.91
5 35 1.82 5.56 1.95
6 38 3.39 10.38 3.95
7 40 5.70 17.46 6.99
8 50 6.17 18.91 9.46
9 52 3.38 10.35 5.38
10 48 4.99 15.31 7.35
Total 32.63 100.00 40.93
AveragePreci itation = 40.93 mm
-
8/18/2019 Module 1_Hydraulic Cycle, Rainfall & Runoff Process 2016
50/50
Question?