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8/8/2019 Intro Sldes
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GEO2
05
GEO2
05Int
roduct
ionto
Hydroge
ology
Introd
uction
toHydrog
eology G E O 2 0 5G E O 2 0 5 Introduction to Hydrog eologyIntroduction to Hydrog eology
Berhanu Fanta AlemawPhD (Hydrology & Water Resources Engineering) -1999MSc (Water Resources Engineering) 1995
BSc (Civil Engineering) - 1990
Geology Department
Universi ty of Botswan aUnivers i ty of B otswana
Course Outline Part A
Part A-1 IntroductionLecture 1 Introduction: Hydrology defined; The hydrologic cyc le;The hydrologic budget; Hydrologic models; Hydrologic data;C o m m o n u n i ts o f m e asu re m e n t
Part A-2: Introduction to components of the hydrological system andbasin water balance (concept, measurement and analysis)
Lecture 2- Basin prec ip itat ion,Lecture 3- EvapotranspirationLecture 4- Su b-surface wa ter ( in f i l trat ion and soil moisture) and
recharge;Lecture 5- Surface water and streamflow
Introduction to Hydrog eologyIntroduction to Hydrog eology Part APart A --11
Object ives (Lecture 1)Object ives (Lecture 1)
Hydrology reviewedHydrology reviewed
Hydrological cycleHydrological cycle
Global water balancesGlobal water balances
Water budgetWater budget
Hydrologic data and units of measurementsHydrologic data and units of measurements
Examples on water budget (massExamples on water budget (mass--balance)balance)calculationscalculations
Hydrology Defined
Hydrology is an earth science.
It encompasses the occurrence, distribution,movement, and properties of the waters ofthe earth
The three branches of hydrology are:
Meteorology -Atmospheric water (rainfall and weather-related processes)
Surface water hydrology - Surface water hydrology(over land surfaces)
Hydrogeology groundwater hydrology (vadosezone/soil moisture & groundwater)
Water Flow Paths:
www.usda.gov/stream_restoration/chap1.html Fig. - 2.10
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Water and water resources the hydrological cycle
More on hydrologic cycle
The Role of water in sustainable development The Hydrologic cycle
Annual volumes of flow given in units relative to the annualprecipitation of the earth (119,000km3/year=100units).
Concept of Water BudgetGlobal Water Balances
5 days0.0030.00008Plants
9 days0.040.0009Atmosphere
7 weeks0.050.0012Soil water
2.26 yrs0.30.008Surface water
5,400 yrs30.90.79Ground water
12,000 yrs68.71.75Glaciers
2,643 yrs-97.5Salt Water
Fresh waterSalt water
Residence
Time
Percentage
of
Reservoir
Global
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Scale in Water Balances
o Spatial ScaleWatershed (smaller catchment eg. Lotsane at Palapye,small drainage project, eg, culvert, road/ bridge crossing astream
Catchment (intermediate basin eg. Motloutse)
Basin Scale (Main drainage basin, eg. Limpopo)
o Temporal Scaleo Seconds, minutes, hours, days, (storms, floods)
o Months, seasons, (water avaiability, storage)
o Annual, decadal, century (climate variability, climate change,land use change effects)
Water balance at a catchment scale
What is a catchment/drainage basin?
A drainage basin is an area surrounded by acontinuous topographic divide within which all runoffjoins a single stream and extends downstream to thepoint that the stream crosses the divide
Usefulness of concept of a catchment
to understand water balances
to understand processes
Example: inflows, outflows and storage processes
Watershed
A basin, drainage or
catchment area that is
the land area that
contributes runoff to
an outlet point
Outlet pointWatershed
boundary
A catchment and watershed divide
27.05 E 27.1 E 27.15 E 27.2 E 27.25 E 27.3 E
-20.9 S
-20.85 S
-20.8 S
-20.75 S
1050 m1055 m
1060 m
1065 m
1070 m
1075 m
1080 m
1085 m
1090 m
1095 m
1100 m
1105 m
1110 m
1115 m
1120 m
1125 m
1130 m
1135 m
1140 m
1145 m
1150 m
1155 m
Nyamabisi Catchment - Elevation in meters a.m.s.l.
Derived from remote sensing radar data Shuttle Radar Topography Mission (SRTM) digital terrain model
Processes in a catchment
Precipitation
Evaporation/transpiration (evapotranspiration)
Surface runoff
Groundwater flow
Storage on the ground surface and subsurface
Soil moisture
etc
Hydrological model as a system
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Hydrological model as a systemWater balance at a catchment
Water balance
1. Hydrologic budget above the surfaceP + R1 R2 + Rg - Es - Ts - I = Ss (1.1)
2. Hydrologic budget below the surfaceI + G1 G2 - Rg - Eg - Tg = Sg (1.2)
3. Hydrologic budget for the region (Add Eq. 1.2 and 1.3)P - (R2 R1) - (Es + Eg) - (Ts + Tg) - (G2 G1) = (Ss + Sg) (1.3)
hydrologic budget for a region can be written simply as
P R G E T = S (1.4)
subscripts s=surface,g=subsurafce
P=precipitation and net R=surface flow, G=underground
flow, E=evaporation, T=transpiration, and S=storage,
Consider Gaborone dam
Storage/Water balance components:
Inflow from Notwane river
Downstream release
Water supply
ET
Lake Evaporation
Consider annual and monthly fluctuations
Water budget/Mass balance or continuity equation
A system, take the Gaborone dam, with inputs that has
outputs is represented by the following equation:
Inputs- Outputs=change in storage
Pt + Qt (Rt + ETt + Wt) = (St-St-1)/[t- (t-1)]
Volume ,St
Release Rt
K, storage capacity
Notwane
inflow, Qt
Wt, Water
supply
Pt Et
Water budget terms
Think of a bathtub:How many litres in the tub = V ? (storage)
How fast do you fill the tub, in litres per minute = Q? (flowrate or discharge)
How long does it take to fill V at the rate of Q? (time)
Watershed Budget: Q = P - ETQ = streamflow out of watershed
P = precipitation onto watershed
ET = evapotranspiration loss = water loss by plants and soil
[A watershed is the area that contributes to a river or stream]
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Water budget ctdExample: Say we have 50cm of rain and 35cm of plant/soil loss
in one yearP = 50cm/yr
ET = 35cm/yr
Q =P - ET = 50 - 35 = 15 cm/yr
We convert this depth per time (D) to a volume per time (Q)How? By multiplying by the watershed area!
Q = A x D
Hint: If you add 10cm to your bathtub, how do you get the volume of wateryou added?
The volume is the base times the height
Think of it as spreading the water out over the watershed
The depth is the height
The base is the watershed area
Water budget ctdExample: Say we have a streamflow depth of 15cm/yr from a 640ha watershed,
what is this streamflow rate in km3/yr?D = 15cm/yr
A = 640 000 ha
Q = 9 600 000 ha-cm per year = 9.6*106*ha cm* (10-2 km2/ha) cm *(10-5km/cm)/yr =0.96km3/yr
Conversion of Units1 ha = 10 000m2 = 10-2 km2 1 cm= 10-2 m = 10-5 km
You probably wonder what a ha-cm is:It is equal to one cm of water that covers one hectare of land
Can you observe what can be asked!
Gaborone dam has what volume in ha-cm?
How much water does the Pandamatenga agricultural field consume in one year?
What is the annual water consumption for Gaborone City Residents?
Let s do this in class: If I have a 10-hectare golf course, and I put on 3cm of water every week, how manym2-cm is this?
How many m3 of water is this?
If water bill is P2.50 per m3, what is the monthly bill to irrigate my Golf Course?
Water Resources
Surface water resources:
Rivers
Lakes and seasonal pans
Dams
Wetlands,
springs
Groundwater resources:
Boreholes
WellfieldsAquifers
Water Availability
19501960197019801990200020102025
103 m3/yr/capFrom: Shiklomanov [http://espejo.unesco.org.uy/]
Water Demand - Botswana (Mil m3/Yr)[National Water Master Plan 1991]
Category Consum-
ption 1990
Demand
2000
Demand
2020
Settlements
(Domestic)
36 78 175
Mining andEnergy
23 36 64
Livestock 35 45 44
Irrigation &
Forestry
19 29 47
Wildlife 6 6 6
Total 119 194 336
Problems in water projects
How much water is needed ?
How much water can be expected? [Minimum flow,Annual yield, Flood peaks,Flood volume, Groundwater]
Who may use the water?What kind of water is it? [Chemical, Bacteriological,Sediment]
What structural problems exist? [Geology, Dams,Spillways, Intakes, Channel works, Pipelines, Canals,Pumps, Turbines, Purification]
Does project affect wild life or natural beauty?
Is the project economic?
http://water/http://espejo.unesco.org.uy/]8/8/2019 Intro Sldes
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Facilities in Water Projects
Control of excess water
Flood mitigation/Storm drainage
Bridges,culverts
Sewerage
Conservation (Quantity)
Water supply
Irrigation
Hydropower
Navigation
Conservation (quality)
Pollution control
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