Sustainable Groundwater Resources Management
Wolfgang Kinzelbach, Philip Brunner*IfU, ETH Zürich
* now Flinders University, Australia
Cooperants in China: Dong Xinguang, Xinjiang Agricultural UniversityLi Wenpeng, Geoenvironmental Monitoring Institute
Contents
• Sustainability in the groundwatersector
• Model uncertainty• Recharge determination• Case study
– Yanqi Basin, China• Conclusions
Concepts in Water ResourcesManagement
• Traditionally: Mainly optimization of narrow monosectoral systems
• Efforts to get to a broader concept:– Sustainability (Rio)– Integrated Water Resources Management
(GWP, Dublin, Stockholm)– Water framework directive (EC)
• General concepts, which have to begiven concrete meaning in every singleapplication
Sustainable Water Management
Management practice, which generally– avoids irreversible and quasi-irreversible
damage to the resource water and thenatural resources linked to it and
– conserves in the long term the ability of theresource to extend its services (includingecological services)
Sustainable Developmentin a broader sense
Includes:
- conservation of the environment, - economic efficiency, and - social equity
Even more difficult to define! Easier to say what is not sustainable than whatis…
What is not sustainable?Non-sustainable is a practice, which is hard to
change and cannot go on indefinitely withoutrunning into a crisis
Non-sustainability shows in- depletion of a finite resource, which cannot be
substituted (groundwater, soil, biodiversity)- accumulation of substances to harmful levels
(salts, nutrients, heavy metals, etc.)- unfair allocation of a resource leading to
conflict (upstream-downstream problem)- runaway costs
The most serious problems of non-sustainability in the water sector on
a global scale:
(all somehow related to groundwater)
Depletion of aquifers1/4 of withdrawals non-renewable40% of irrigated agriculture affected bydeclining groundwater levels
General Principle
• Withdrawal < Recharge (from precipitation and surface waterinfiltration)
Do not forget the downstream (users, ecosystems):• Withdrawal < Recharge – Minimum downstream
requirements (or commitments)
View of groundwater basin
Recharge areas – Discharge areas
An aquifer is not a new resource but only a storage devicewith inflows and outflows. Inflows are distributed among different
outflows (streams, springs, wells, evapotranspiration) the sum of which is fixed. We can only redistribute!
Fallacy of large volume of reservoirsunder deserts
Falling groundwater levels lead to- Increase in price- Attraction of saline water
- from deeper aquifer- from salt lakes
Main Cause for Water Table Decline:Large Scale Irrigation with Groundwater
Examples:
Ogallalla Aquifer, USANorth China PlainKaroo Aquifers, South AfricaAquifers of the Arab PeninsulaChad Basin aquiferNorthern Sahara Aquifer System (SASS)
Typical rates of decline 1 to 3 m/a
Related sustainability constraints
Limitation of drawdowns because of– vegetation– land subsidence– collapse of fractures– energy cost
Of concern long before aquifer depletion!
Decline of groundwater table leads todestruction of phreatophytes.
5-m safety Pump intakelevel
Main waterstrike
Cone ofdepression
Rest waterlevel
Groundlevel
Dynamicwater level
Dewatering ofmain water strike
Placement of the pump intake level 5 mabove the main water strike is
recommended to prevent overpumping.
Dewatering of the main water strikecould have been avoided by placementof the pump intake level above the main
water strike.
Availabledrawdown
Dynamicwater level
Decrease of base flow of riverseven large rivers become ephemeral, lakesdry up, upstream-downstream conflictsincrease
Base flow = groundwater discharge
Drying up of wetlandsArea reduced by 50% since 1900 Competitor: Agriculture
A swamp sustains vegetation through groundwater recharge
Soil salinization80 Mio. of 260 Mio. ha irrigatedland in some way affected
Causes of soil salinization
water, saltswater vapour
Without drainage: Accumulation of salts
natural
irrigated
Groundwater table rise, capillar rise,high evaporation and salt deposition
water, salts
In general Most relevant mechanism(also in Yanqi)
NMediterranean Sea
Polluted area, 1957
Polluted area, 1995Libyan mainland
0 5 kmScale
Almaya
Janzur
Gargaresh
Ayn Zara
TajuraTripoli
Pollution of groundwater with persistent orrecyclable pollutants
Main groundwater pollutants
Bacterial pollutionSalinityMineral oil productsChlorinated hydrocarbonsNitratePesticides…..
Seawater intrusion
Salt waterFresh water
Saltwater upconing
Salt waterFresh water
Salt Water Upconing on Wei Zhou Island
Thesis Li Guomin
Upconing
Fresh Water Lens
Alternative Extraction Strategies
• Conceptual and numerical model describing the system
• Possibly flow and transport• Coupling with surface and soil water• Possibly coupling with economic model• Calibration with observation data• Optimization and prediction
Basis for sustainablegroundwater management
How to check for sustainability?
Fix system parameters and boundary conditionsDefine human stresses or management decisions
Run system model to time t → ∞
Check whether solution exists with final state beingacceptable with respect to predefined indicators: environmental, health , economic, social …
Steady state?
Not necessarily static!
Time Time
Problems• Groundwater cannot be modelled alone but must becoupled to other resources and economics• System parameters and boundary conditions maychange in time (e.g. climate, population, livingstandard and definition of what is acceptable ...)• System parameters and boundary conditions areuncertain (measurement errors , upscaling, heterogeneity, unknown future values)
Consequence: Sustainable practices requireadaptability and robustness
Special problems in arid regions
• Recharge– in humid zone: error maximum 50%, in arid zone: factor 10
• Rivers as fixed heads– rivers are often seasonal
• Importance of evaporation and evapotranspiration– Existence of sinks obvious, but fluxes not visible
• System not in steady state– Assumption of steady state may lead to wrong conclusions
• Low density of observations– Interpolation critical
• Result: large uncertainty of models
Uncertainty of models
• Conceptual uncertainty• Parameter uncertainty• Uncertainty of calibration• Uncertain future hydrology• Uncertainty in economics
Ways out:
• Conservative design• Stochastic modelling and risk based decisions
Q=b*T*I
Parameter uncertainty
Q=b*T*I
Parameter uncertainty
Project area Gambach, Germany Thesis Vassolo
Given:AquiferWanted:Catchmentof wells
Sealed (no recharge)Basalt (180 mm/a)Loess (90 mm/a)
Rechargedistribution:3 uncertainvalues
Transmissivitydistribution:7 uncertainvalues
Headdistributionfor oneparameterset (realization)
Catchment1 realization
Catchment3 realizations
Probabilitydistribution of catchment shapefrom manyrealizations
Probabilitydistribution of catchment shapefrom manyrealizationsConditioned withobserved heads
Determination of recharge• Single most important figure for sustainable
management• Water balance methods and Darcy formula
notoriously inaccurate (factor of 10)• Environmental tracers can often be better
(factor of 2-3) • Tracers used: Tritium, Tritium-3He, CFC
(Freons), SF6, Chloride• Combination with remote sensing to get from
point values to areal values
Input Output
Time Time
u = L/τ
delay τ
L
One principle of dating with tracers: Use transients
Result:Pore velocity
With porositywe obtainspecific flux
Bomb 3H peak at different latitudes
0
500
1000
1500
2000
2500
3000
3500
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995
Year
annu
al a
vera
ge 3 H
(TU
)
Ottawa
Bamako
Pretoria
Khartoum
F11
F12
ATMOSPHERIC CFC CONCENTRATIONS ON THE SOUTHERN HEMISPHERE
Sampling for CFC in groundwater (Niger)
Combination of methods fordetermination of recharge
• Water balance method (hopelessly inaccurate butareally accessible with remote sensing)
• Chloride method (hopelessly local but quantitativelymore reliable)
Recharge = Precipitation - ET
Recharge = (D + cp*P)/cR
MS-thesis BrunnerWhy not combine the two?
Thinking in water balances
For simplicity of argument: Consider an areawithout outflow and with no trends in piezometricheads. Then the long term average requires:
Precipitation = ETor
Recharge = Discharge
Only positive recharge can be calibrated withchloride data
Maun
Nata
Shakawe KasaneKavimba
Maun
Nata
Shakawe KasaneKavimba
Example: Kavimba, BotswanaSatellite image and river system for orientation
NOAA-14 image of June 18, 2000, AVHRR channel 3
Precipitation sum of year 2000 from METEOSAT5 (FEWS)
Map of the daily total evapotranspiration ET24 [mm d-1]
From image of July 19, 2000, 16:28 using SEBAL algorithm(white pixels are water surfaces where no NDVI was calculated and hence no ET24 can be determined)
- 17.5
- 18.5
23.5 24.5
10-year Average of Precipitation-ET (mm/yr)(from 97 images)
Recharge rates from chloride method („ground truth“)
60 chloride samples from boreholesAverage chloride concentration: 21 mg/l
⇒ Average recharge: 6.8 mm/yr
0.1
1.0
10.0
100.0
1000.0
10000.0
0 10 20 30 40 50 60
Sample number
Chl
orid
e (m
g/l)
y = 0.057x - 0.8448R2 = 0.734
-5.00
0.00
5.00
10.00
15.00
20.00
25.00
-100 0 100 200 300 400
Average Net Exchange (mm/yr)
Rec
harg
e by
Chl
orid
eM
etho
d (m
m/y
r)
Recharge distribution from combination
Only for areawhere surfacerunoff is neglible
Area with non-negligiblesurface runoff
(mm/a)
Conditioning of Stochastic ModellingApplication to Kavimba Aquifer
Data:• Transmissivities from pumping tests and variogram• Head observations• Digital terrain model• Recharge distribution from remote sensing plus its errorfrom correlation analysis
Two variants with 300 realizations each:• A: without using recharge distribution• B: with recharge distribution as conditioning data
Application to Kavimba Aquifer
Results:
Ensemble of realizations μlogT σlogT μR σR σh
A (without remote sensinginformation)
-2.36 0.71 6.5 8.0 16.0
B (with remote sensinginformation)
-2.38 0.61 6.4 3.3 10.3
Uncertainty reduction in input and output variables
Ensemble standard deviations of transmissivity, recharge and head
Soil salinization and ecologicalwater demand in the Yanqi Basin,
Xinjiang (China)
First Control PointKaidu River
Bostan Lake
Kongque River
Qing Shui River
Second Control Point
Huang Shui River
The Yanqi Basin and its problems
Decline of water level in lake
Die-off of fish
Increase of salinity in lake
(due to doubling of population over the last 50 years)
Soil salinization
Groundwater table rise due to irrigation
Drying up of „green corridor“
• Reduction of irrigated area• Alternative crops• Improvement of water efficiency of irrigation• Deep drains and other drainage measures• Increased proportion of groundwater for irrigation• Lowering of lake water level
Possible measures to improvesituation in Yanqi
Government directiveRestore downstream flows for nature of 1985
Units: m3/sWater balanceResources to be harnessed:Unproductive evaporation Savings in irrigation water
Reduction of evaporation of lake
Salt fluxes in and out of basin (104 t/a)
Model concept
Four layer aquifer coupled to rivers and lake
Inflows: Seepage from rivers, seepage from irrigationOutflows: Evaporation from groundwater, pumpingdrainages, exfiltration to rivers
Coupling of surface waters and groundwater vialeakage principle, water balance of lakeEvaporation from aquifer: exponential or stepwiselinear function of distance to groundwater tableComputed quantities: Piezometric heads (x,t),
water fluxes, Δ salinity
Four layers, discretization 500 m
Flow model(boundaries and geological structure)
Data sources for model
Radar satellite images
DTM
Distribution of ET
Multispectral sat.-images
Phreatic ET
depth
Salt distribution
Multispectral sat.-images
Remote sensing
Stable isotopes
Field campaigns
Geophysics
+ classical methods
DTM from radar satellite images
Salinization is function of distance ground surface – groundwater table
Mapping soil salinity with remote sensing
Based on the spectrum of extremely saline pixels, a spectral match to that signature is defined :
Scaling with ground truth
Non-irrigated areas
0
20000
40000
60000
80000
100000
120000
140000
160000
0 0.2 0.4 0.6 0.8 1
Spectral match between GCP and Reference
GC
P-c
ondu
ctiv
ity (m
icrS
/cm
)j
Irrigated areas
ET in Yanqi basin year 2000 (mm/a)
Model calibration on the basis of measured and computed heads
Average heads over 5 years
Model calibration on the basis of measured and computed heads
Too inaccurate for computation of phreatic evaporationMain error: digital terrain model
Filtering required
Comparison of measured and computed distance to groundwater
Model calibration on the basis of measured and computed phreatic evaporation patterns
Model
Evaporation function of distance to groundwater tableFormula from stableisotopes
Remote sensing
Separation of ET and E usingNDVI andstable isotopes
Model calibration on the basis of measured and computed evaporation
Subscale variability of DTM (100 m x 100 m) takeninto account. Averaging over 4 km x 4 km
Results of scenarios (at steady state)
No irrigation Present Pumping
1232
15.3
26.612.646.1
1.2
Flow to green corridor m3/s 69.1 38.9 53.0
Salinity of outflow g/l 0.8 1.4 1.0
P + watersaving
Total salinized area (s-h < 2m)(km2)
846 1720 1036
Phreatic evaporation m3/s 10.3 22.5 12.3
Irr. water diverted m3/spumped m3/s
--
36.22.6
22.912.1
Evaporation from aquifer in pumping scenario(ΔQ = 10 m3/s, start in 2000)
Increase of downstream flow by 0.75 m3/s per 1 m3/s of groundwater pumped
m3/s
Time
E
Salt concentration in pumping scenario(Approach to steady state conditions)
c1 salt concentration in saline first layer
c2 salt concentration in pumped second layer
cmix salt concentration in irrigation water (average GW-SW)
year 0↔year 2000
Condition for sustainability of pumpingscenario
Efficiency of drainage net and final salt deposition in saltmarshes must be maintained
Flux from layer 2to layer 1
Valuation of alternativesCosts:
Energy for pumping, cost of wellsEquipment for water savingirrigation
Benefits:Less salinized areaEcological benefit (lake and green corridor)Road connection to Qinghai sand free
Quantification and societal preferences in general difficultto determine. Work in progress
Comparison of some cost figures
• Agricultural prod. value Yanqi Basin 820 Mio. Y/a• Agricultural production possible with incremental
water released to downstream in pumping scenario170 Mio. Y/a
• Additional water cost due to pumping 80 Mio. Y/a • Road protection cost (in analogy to Takla Makan
Highway): 19 Mio. Y/a• Cost of ecological releases: 84 Mio. Y/a• Government goal to go back to 1985 situation
means hardly any change for Yanqi basin as bigwater transfer from natural ecosystems to agriculture happened before that time
Future problems
- Portion of glacier melt presently up to 30% of flow- This part is missing after complete retreat of glaciers- Precipitation in Tianshan will probably increase 25%- Population will be stable only after 2050
Conclusions Yanqi Basin• Solutions for the salinization problem without production
losses exist, but they involve higher cost. Implementationonly realistic if food prices increase.
• Larger water allocation to the ecosystems is feasible byharnessing the unproductive evaporation fromgroundwater and water saving irrigation.
• The single plot can always be managed sustainably, but at very high water consumption and under export of problems to the downstream. Sustainability requiresanalysis of the whole system including the downstream.
• The ecological benefits (lake, green corridor) are difficultto quantify. Costs seem high.
• For downstream salinity reasons there is a limit to irrigation even if phreatic evaporation is under control
• Future developments probably aggravate situation
General conclusions• Sustainability is a difficult concept, which has to be
defined anew in every situation. • Given sufficient system knowledge the model
based analysis of a system with respect to sustainability is feasible
• Methods of integral regional modeling are availableor in development
• The data and calibration problems can be reducedby new data sources such as e.g. remote sensing
• To be really useful, hydrological models have to becoupled to economic models
N
S
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Ecological Water Release
Bostan Lake
Lop-Nur Lake
Taitema LakeQarqin River
Daxihaizi reservoir
Replacing surface reservoirs bygroundwater reservoir
• 1.8 Billion m3/a total flow• Ca.1250 km2 aquifer area• Ca. 6000 km2 crop area• 450 Mio. m3 surface storage volume Lake Manas
The aquifer• 35 billion m3 storage volume assuming a porosity of 15%• Average thickness: ca. 190 m
The ideaSchematic illustration of possible aquifer management
Seepage
Drainage
Irrigation
Inflow
Outflow
Reversal-point
0 5 km 10 km
Pumping
January 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
February 1st
Drawdown in m
Drawdown of heads compared to January 1st (in m)
Simulation
March 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
April 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
May 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
June 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
July 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
August 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
September 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
October 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
November 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
December 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
January 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
February 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
March 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
April 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
May 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
June 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
July 1st
Drawdown in m
Drawdown of heads compared to January 1st (in m)
Simulation
August 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
September 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
October 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
November 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
December 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
January 1st
Drawdown of heads compared to January 1st (in m)
Simulation
Drawdown in m
Result• Feasible water savings
– If all surface reservoirs are replaced (450 Mio. m3):124 Mio. m3/a (or about 10% of total flow of Manasriver)
– Minimum goal (116 Mio. m3): 39 Mio. m3/a
