Perspectives of Water Resources Systems

Development and Operation in SA

PACBP

By Beason Mwaka 27 March 2013

Need for the WR Systems

• Storage and conveyance infrastructure like dams & pipelines required for water redistribution over time and space

• Infrastructure like dams also necessary to increase yields for the ever growing socio-economic developments & environmental water needs

Uneven spatial distribution of SA’s water availability

Areas of main national economic activities do not match

areas endowed with sufficient water availability

Recognizing water a national resource, and mismatch between availability & demand, necessitate regulation and/or transfer

systems like dams, pumps, canal, etc.

SA Water availability is limited & temporally distributed in time

857 mm

WORLD

80 % in 5

MONTHS

470 mm

SOUTH AFRICA

10 000 mm

HAWAII

Approx. Water Balance: Resource vs. Requirements

Country Annual Water Requirements (km3/yr) Available Resource (km3/yr) 1993 2020

Angola 1.335 2.757 78.000

Botswana 0.129 0.336 0.230 Lesotho 0.118 0.268 2.490 Malawi 1.135 2.578 4.240 Mozambique 1.967 3.210 132.000 Namibia 0.265 0.538 0.740 Swaziland 0.454 0.511 1.160 Tanzania 5.374 12.220 44.000 Zambia 0.994 2.192 60.000 Zimbabwe 2.524 5.737 7.860 South Africa 19.295 30.168 28.470

Historical Perspectives of Water Resources Development in SA

1. At start of 20th century, notable water abstraction largely for irrigation

2. Run-of-river abstractions sufficed without need for regulation systems

3. After World War 1 & drought of 1929 development for irrigation systems was accelerated

4. More irrigation, mining, growing town centres, etc., led to multi-use regional water schemes

Legislative Developments 1. Based on concepts of freehold land & riparian right,

land owners were entitled to water on their property

2. This principle formed the basis of 1912 Irrigation & Conservancy Act, with Special Water Courts created to apportion water rights

3. As Industry & Urban water requirement grew, the agriculturally centred law became less appropriate

4. The 1956 Water Act was introduced to bring an element of State control on water resources, but still recognising the laws of private ownership made by Water Courts

5. It’s the 1998 Water Act that instituted the principle of water being a national resource belonging to all in SA

Water Requirement projection (Rand Water) Recognition that water is a basic human right

RI =

1:2

00 y

ear

RI =

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ear

RI =

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0 ye

ar

RI =

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ar

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Reliability of supply (as % of sequences observed)

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0

Yiel

d / t

arge

t dra

ft (m

illion

m3 /a

)

Firm yield line

Hydrological analysis done to determine system yields for various target drafts

Lower demand high probability of supply

Higher demand lower probability of supply

Existing System Yield (Including Growth in Darvill

Return Flows)

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400

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2004 2006 2008 2010 2012 2014 2016 2018 2020 2022 2024 2026 2028 2030

Hydrological analysis & reconciliation plans of developments for projected requirements

12

Wat

er R

equi

rem

ents

/ Yi

eld

(milli

on m

3 / a

nnum

)

Spring Grove Dam

Re-use of Treated Effluent

Mkomazi River Development (Smithfield Dam)

Deficits

November 2010 Water Requirements

Scenario

Pipeline from Spring Grove Dam

Based on selected reconciliation plan 1. Feasibility study & preliminary designs of the

project for optimal solution 2. EIA for measures to address social & environmental impacts due to the project 3. Funding model & institutional arrangements 4. Authorization requirements – from DEA, Parliament/cabinet, Land restitution/rights, etc. 5. Implementation

- Challenge is that available water resource is finite - Feasible options to increase yield diminishing

- Below is dam (storage) development in last century

160 27 31729

3538

2691146

30743763

2894

171

16693

0

2000

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6000

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10000

12000

14000

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18000

— 1900 1901-1910 1911-1920 1921-1930 1931-1940 1941-1950 1951-1960 1961-1970 1971-1980 1981-1990 1991-2000 2001-2007

Time [yrs] since development started

Wa

ter S

tora

ge

Ca

pa

cit

y o

f d

am

s [

Mm

3]

160 187 218

4484 4753 58998973

25666

2943032323 32495

947

0

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35000

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45000

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60000

—1900 1901-1910 1911-1920 1921-1930 1931-1940 1941-1950 1951-1960 1961-1970 1971-1980 1981-1990 1991-2000 2001-2007

Time [yrs] since development started

Wate

r S

tora

ge C

ap

acit

y o

f D

am

s [

Mm

3]

Total Water Potentially available

Controllable water (available for operation)

Uncontrollable water (not available for operation)

Water Demand vs. Yield

0

100

200

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700

1980 1990 2000 2010Years

Wat

er D

eman

d

Development Phases with summary of associated management challenges

Natural Phase 1920 <

•1. Water not limited

•2. Management institution not necessary

•3. Data not important

•4. No systems to manage

•5. No link with groundwater & others

Development 1920 - 2000

• Water only commercially limited

•Technical management from top

•Data necessary for sizing infrastructure dev

•Management of infrastructure systems

•Groundwater employed to supplement surface water

Allocation Phase >2000

•Water is limited physically

•Institutional arrangement requiring stakeholder participation

•Data needed for equitable allocation of water

•Management of the whole river system environment

•Water mix resources used conjunctively

Water Resources Systems Operation

• Systems operation is the regulation (of gates, pumps, etc) to control water storage & movement

• An operating rule is an instruction for controlling the systems. My be graph, equation, statement, etc

• Its purpose is to achieve three broad goals: – Supply water as per requirement schedules (mainly)

– Control flow/storage to mitigate against risks

– Minimize losses and improve equity

Water resources operating factors

– 1. Hydrology (rainfall, river flows, reservoir levels, etc.)

– 2. Water requirements (e.g. irrigation, municipal, reserve, etc)

– 3. Infrastructure (maintenance schedules, configuration, etc)

– 4. Water resource quality

– 5. Cost

Wet season

Dry season

DSL

FSL

Drought

- Desirable

- Controllable

- Measurable

INPUT

OUTPUT

- Desirable

- Controllable

- Measurable

Floods

Principles of Operating Rules for Water Supply Management

• Operating rules determined annually on basis that water is an annually renewable resource

• Water requirements based on annual business plans

• Annual water availability & demand determined & allocated in both volume & risk

• In drought, restriction implemented to sustain critical (priority) users for longer

• Models or DSS facilitate to achieve optimal performance

Short-term yield curves water allocation management DSS

Hluhluwe Dam supply performance for various target drafts

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

5 10 15 20 25

Target Draft (Mm3/year)

ratio

volume supplied / volume demanded

time that supply is unrestricted / total period ofanalysis

Mandate

1. The National Water Act of 1998, e.g.

a, Water Boards, WUAs, etc, may temporarily control, limit or prohibit use of water …., but in so doing must provide information on extent of disruption, etc. (Schedule, 3 Sec. 6,

NWA)

b, The public need to be informed of risks posed due to anticipated droughts, floods, pollution incidents, etc. (Sec 145, NWA)

2. The Water Services Act of 1997

- Municipal bylaws

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Year Ending

W-Cape: Berg: WMA 19 1979/80 to 2010/11

Mean Rainfall (%Mean) Oct Storage (%FSC) Linear (Mean Rainfall (%Mean)) Linear (Oct Storage (%FSC))

Empty Berg River Dam brought into "Weekly" calculations (6 Aug 2007)

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Year ending

Berg: WMA 19

1979/80 to 2010/11

Oct Storage (%FSC) at end of Rain Year Mean Annual Rainfall (%Mean) Based on District Rainfall

The END