Intro Sldes

8/8/2019 Intro Sldes

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GEO2

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GEO2

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Hydroge

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Introd

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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
http://www.usda.gov/stream_restoration/chap1.html


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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/]


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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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