 1
Contents
w
Global ground water situation
w
What does sustainable mean in terms
of groundwater?
w
Tools for recharge determination
w
Models and uncertainty
w
Interfacing to economics
w
Conclusions
2
Global water availability
w
Accessible runoff 13000 km3/a
w
Human withdrawals 4000 km3/a
w
Human in stream use 3000 km3/a
w
Groundwater available 2500 km3/a
w
Groundwater used 800 km3/a
w
Depletion of groundwater reservoirs
100 km3/a
3
Averaging is misleading
4
Stored Volume vs. Renewal Rate
of
fresh water resources
4.1
Surface water (lakes and rivers):
w
Volume
104,000 km3
w
Renewal rate
30,000 km3/a
4.2
Groundwater:
w
Volume
10,000,000 km3
w
Renewal rate
3,000 km3/a
5
Structure of Water Use
w
Agriculture 69% (90%
consumptive)
w
Industry 23% (20% consumptive)
w
Domestic 8% (20% consumptive)
6
Groundwater is special¡
w
Groundwater use is much smaller than
surface water use, but
w
Groundwater is a strategic resource
for drinking water in the arid and semi-arid world
w
Groundwater is practically the only
resource available year round
w
Sustainability problems are most
severe in groundwater both in the context of quantity and quality
w
The feasibility of increasing the
resource is low
7
SUSTAINABILITY CONSTRAINTS
w
Abstraction < Recharge
w
Limitation of drawdowns (vegetation,
subsidence, collapse of fractures)
w
Prevention of saltwater intrusion/upconing
w
Prevention of soil salinization, salt
backflow
w
Guarantee of minimum downstream flow
(wetlands, vegetation, users)
w
Prevention of groundwater pollution
8
GENERAL PRINCIPLE
w
Withdrawal (Consumptive use) <
Recharge (from precipitation and surface water infiltration)
w
Considering the downstream:
Withdrawal < Recharge¨CMinimum downstream requirements
9
Main Cause for Water Table Decline:
9.1
Large Scale Irrigation with Groundwater, Examples:
w
Ogallalla Aquifer, USA
w
North China Plain
w
Karoo Aquifers, South Africa
w
Aquifers of the Arab Penninsula
w
Chad Basin aquifer
w
Northern Sahara Aquifer System (SASS)
9.2
| ¡¡ |
| ¡¡ |
 |
Typical decline rates 1 to 3 m/a
10
SALTWATER UP CONING
11
| ¡¡ |
| ¡¡ |
 |
SALINIZATION DUE TO HIGH GROUNDWATER TABLE
12
SCIENTIFIC TOOLS FOR SUSTAINABLE AQUIFER MANAGEMENT
12.1
Methods for the determination of groundwater recharge
w
Environmental tracers
w
Remote sensing
12.2
Models and coping with uncertainty
w
How to use models
w
Quantification of uncertainty
12.3
Interface to socio-economic analysis
w
Common pool
w
Discounting
13
ENVIRONMENTAL TRACERS FOR RECHARGE DETERMINATION
w
Tritium
w
Tritium-Helium 3
w
Chlorinated-Fluorinated Hydrocarbons
w
SF6
w
Chloride
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
14
Combination of methods for determination of recharge
w
Water balance method (hopelessly
inaccurate)
R = P ¨C ET
w
Chloride method (hopelessly local)
R
= (D + cp*P)/cR
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
15
SCIENTIFIC TOOLS FOR SUSTAINABLE AQUIFER MANAGEMENT
15.1
Methods for the determination of groundwater recharge
w
Environmental tracers
w
Remote sensing
15.2
Models and coping with uncertainty
w
How to use models
w
Quantification of uncertainty
15.3
Interface to socio-economic analysis
w
Common pool
w
Discounting
16
Why
Models
w
Interpretation of data
w
Interesting quantities only
indirectly known
w
Predictive capability
w
Ease of scenario analysis
w
Integration of all knowledge in one
framework
w
Creating coherence in projects
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
17
TYPICAL WEAKNESSES OF MODELS
w
Uncertainty of parameters
w
Non-uniqueness of calibration
w
Unknown hydrological future
w
Uncertainty of conceptual model
w
 Way
out: Stochastic approach
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
18
Quantification of Uncertainty in Recharge Rate
w
Given uncertainty in transmissivities
and observed heads
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
19
SCIENTIFIC TOOLS FOR SUSTAINABLE AQUIFER MANAGEMENT
19.1
Methods for the determination of groundwater recharge
w
Environmental tracers
w
Remote sensing
19.2
Models and coping with uncertainty
w
How to use models
w
Quantification of uncertainty
19.3
Interface to socio-economic analysis
w
Common pool
w
Discounting
20
Tragedy of ¡°the commons¡±
¡¡
21
Alternative Approaches to Sustainability Needed
w
Traditional neoclassical approach to
optimal resource use (economic efficiency):
Maximize the Present
Discounted Sum of Net Benefits
¨CUsed Extensively in
Cost-Benefit Analysis of Projects and Economic and Environmental
Policies
w
Main deficiency: costs and benefits
in the distant future make no difference
w
Alternatives to the traditional
approach give more value to the future
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
22
 Options
(Potential in km3/a) (compare
to 4000 km3/a)
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
w
Water saving (agriculture1000,
industry 160, households ...)
w
Water conservation methods including
rain harvesting (1000)
w
Change of diet (?)
w
Change of economic activity and
import of „virtual water¡° (presently ?)
w
Desalination (presently 20)
w
Inter basin transfer (100)
w
Reallocation of people, population
policies (presently 6)
w
Gaining time by non-sustainable
exploitation (presently 100)
23
Conclusions
w
Sustainable management of aquifers is
a burning problem
w
New scientific tools are available to
support the definition of sustainable water use
w
Modeling will play a major role
w
The stochastic approach allows us to
stay humble
w
Natural science has to interface to
economics and implementation in order to be really useful
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
¡¡
|
