recharge in arid and semi-arid regions · 2018-09-13 · chyn-unine recharge in arid and semi-arid...
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CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
RECHARGE IN ARID AND SEMI-ARID REGIONS
Case study: Nubian Sandstone Aquifer System in Northern Chad
Marie-Louise Vogt
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
WHAT IS RECHARGE
RECHARGEThe amount of water thateffectively reaches the water table
Recharge ≠ Infiltration
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
WHY TO STUDY RECHARGE
• «The abstraction from a groundwater reservoir should in the long term not belarger than the long-term average recharge»
• «Sustainable management with respect to quantity requires that abstraction islimited to a fraction of recharge in order to guarantee a minimum availability of water in the downstream» Kinzelbach et al. 2003
• « A common misperception has been that the development of a groundwatersystem is «safe» if the average annual rate of groundwater withdrawal doesnot exceed the average annual rate of natural recharge. […] safe developmentdepend instead on how much of the pumpage can be captured fromincreased recharge and decreased discharge» Alley and Leake, 2004
• Bank analogy
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
WHY TO STUDY RECHARGE
In arid and semi-arid countries, groundwater constitute an important long-term
storage reservoir, often being the only perennial water resources available
Rocky desert in southwest Jordan
Taklamakan, China
Sonoran Desert after rain Kalahari, Botswana
Australian outbackAtacama, Chile
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
CONSEQUENCES OF OVERPUMPING
• Large drawdowns- > increased pumping costs
• In soft strata, land subsidence
• Reversal of hydraulic gradient
• Sea water intrusion (upconing)
• Soil salinization
San Joaquin Valley, California: Photo: USGSS
W.Kinzelbach
NCGRT
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
NON-RENEWABLE RESOURCES
Non-Renewable Groundwater (Margat et al. 2006): «Groundwater resource available for extraction, of necessity over a finite period,
from the reserves of an aquifer which has a very low current rate of average annual renewal but a large storage capacity»
Fossil Groundwater (International Glossary of Hydrogeology, 1992) : « Water that infiltrated usually millennia ago and often under climatic conditions
different to the present, and that has been stored underground since that time »
Aquifer Overexploitation (Margat & Saad, 1984):« Prolonged (multi-annual) withdrawal of groundwater from an aquifer in
quantities exceeding its average annual replenishment, bringing about a persistent fall in groundwater levels and reduction of aquifer reserves with undesirable side effects »
Groudwater Mining (Margat & Saad, 1984):« Extraction of groundwater from an aquifer having predominantly non-renewable
resources with depletion of aquifer reserves »
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
MAJOR AQUIFERS CONTAINING PREDOMINANTLY NON-
RENEWABLE GROUNDWATER RESOURCES
• North Western Sahara (Algeria, Libya, Tunisia): 1 Mkm2
• Murzuk basin (Algeria, Libya, Niger): 450’000 km2
• Iullemeden Multilayer Continental (Mali, Niger, Nigeria): 500’000 km2
• Chad basin (Niger, Nigeria, Chad, Sudan, Cameroon, Libya): 600’000 km2
• Various (Saudi Arabia, Bahrain, Qatar, UAE): 250’000 km2
• Great Artesian Basin (Australia): 1,7 Mkm2
Reference for «thisvolume»:http://unesdoc.unesco.org/images/0014/001469/146997E.pdf
Nubian Sandstone (Egypt, Libya, Sudan, Chad): 2.2 Mkm2
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
SOME DEFINITIONS - RECHARGE AND DISCHARGE
Lakes of Ounianga, N Chad
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
SOME DEFINITIONS - UNSATURATED AND SATURATED ZONE
Unsaturated zone: (or: Vadose Zone, Zone of Aeration)The zone between the land surface and water table (which may include the capillary fringe). Water in this zone is generally under less than atmospheric pressure, and the voids may contain water, air or other gases.
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
SOME DEFINITIONS - UNSATURATED AND SATURATED ZONE
Saturated zone: (or: Phreatic zone)The saturated zone is that part of the earth’s crust beneath the regional water table or piezometric surface in which all voids, large and small, are filled with water under pressure greater than atmospheric.
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
SOME DEFINITIONS - UNSATURATED AND SATURATED ZONE
AquiferAn aquifer is a geological formation which has structures or textures that hold water or permit appreciable water movement through them.
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
FUNCTION OF AN AQUIFER
An aquifer has three important functions, namely:
Storage - It stores water, underground, as a reservoir. The aquifer characteristic describing
the ability of an aquifer to store water is its porosity. The characteristic describing its
ability to release water under gravity drainage is called its specific yield.
Transmission - It transmits water like a pipeline. The relevant aquifer characteristics which
determine how easily water is transmitted in an aquifer are hydraulic conductivity and
transmissivity.
Mixing - It mixes water of different qualities. A poor quality water can be injected into an
aquifer at one point, mixed with the local groundwater and the mixture withdrawn at
another location as useable water.
Sedimentary aquifer(porous unconsolidated)
Primary porosity
Fractured rock aquifer(granite, volcanic, metamorphic)
Secondary porosity
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
QUICK EXERCIZE
Exercize 1
e = 30 mAquifer unconfinedSurface area of the aquifer 10 km2Specific yield (vol water/vol rock) is 12.5%
Calculate the volume of water that can beextracted if the drawdown was of 5 m across the aquifer
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
SOME DEFINITIONS – PISTON AND
PREFERENTIAL FLOW
• Piston flow: a wetting front of ϴw content of water, infiltrating uniformily into a fairlydry sediment of ϴi
• Preferential flow: fingers, heterogeneitiesin layers, porosities, landscape change
Displacement faults in sand near Socorro, New Mexico. The wet spots coincide with the faults. From J.M. Herrin (September 1997)
Unstable wetting patterns at 0.20 m depth in wettable sand after 403 mm precipitation; dark spots are wet. From Hendrickx and Dekker (1991)
Hendrickx and Flury (2001)
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
SOURCES OF RECHARGE
• Precipitation recharge
• River recharge, including perennial, seasonal
and ephemeral flows
• Irrigation losses, both from canals and fields
• Interaquifer flows
• Urban recharge
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
RECHARGE IN ARID AND SEMI-ARID CLIMATES
• Rainfall tends to be more variable in both space and time
• Small frequency of occurrence
• Short duration
• High intensities
-> Recharge time and space variability : when significant recharge results only from
infrequent large events, it is highly misleading to talk of mean annual recharge or of
recharge as a proportion of mean annual rainfall; empirical rainfall-recharge expressions
can only be applied to specific areas/basins with known hydrologic characteristics
(characteristic of the vadose zone, antecedent moisture, vegetation, precipitation
distribution within and between years, local topography, watershed shape)
• Arid zones are often in a delicate hydrological balance. 95% of precipitation is lost
through evaporation: virgis, interception, soils and evapotraspiration
-> Rates of precipitation and evaporation are very similar: the residual is very small and
with high uncertainties
• Recharge rates and distribution are highly sensitive to the soil cover type and the land
change use
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
MECHANISMS OF RECHARGE
Lucien Blandenier (2015)
In arid and semi-arid cliates determining diffuse precipitation is not straightforward:
size, temporal and spatial variability, direction of water balance fluxes are distinct than
in more humid climates
-> thick unsaturated zone
-> piston flow against preferential flow
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
RECHARGE FROM INTERMITTENT FLOW
Al-Bawada, Saudi Arabiahttp://pages.uoregon.edu/millerm/fan.html
• Recharge by intermittent streams• Recharge of alluvial fans• Hidden recharge
Petra hydrological simulationhttps://www.youtube.com/watch?v=uCak7721ox8
In arid climates, recharge from intermittent flow is the most important source of recharge
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
CRITERIAS TO SELECT A METHOD FOR ESTIMATING
RECHARGE
• Clearly state the objective (future water supplies, vulnerability of an aquifer to contamination) and time required (estimate of coming decades or millennia)
• Take care when defining the conceptual model: most common and serious type of error
• Different sources and different processes of groundwater recharge will guide the selection of the method (or methods)
• Take into account spatial and temporal variability: infrequent major recharge isdifferent than small and regular events; small amounts of precipitation my provokerecharge or not depending on the season when it occurs; a multiple temporal resolution is needed (day, 10-day, month, year, 10-years, etc.)
• In arid climates, rates of precipitation and evaporation are similar, the net amount istherefore small and with high uncertainties; to reduce uncertainties, use multiple techniques
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
METHODS FOR ESTIMATING RECHARGE
1. Darcyan methods
2. Direct measurements: lysimeters, TDR probes
3. Water balance methods: soil moisture budgets, water tablefluctuation method, river channel water balance, river baseflowmethod, spring or river flow recession curves
4. Tracer methods: artificial tracers, environmental tracers (modern recharge: chlorine method, tritium; paleorecharge: 14C, 36Cl, 18O, 2H)
Methods can be grouped into the following classes:
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
COMPARISON OF METHODS FOR ESTIMATING RECHARGE –
DIRECT METHODS
LysimetersA lysimeter is a device consisting of an in situ weighable soil column of a 1m2 or greater cross-sectional area. It measures the flux created by rainfall (diffuse) as the outflow by seepage at 1-2m depth. It is a measure of drainage and not recharge.• High quality data• Point-based• 5-10 years needed for equilibration• Characterizes diffuse recharge
Soil moisture budget by neutron probe (or TDR probes)Soil moisture budget by neutron probe (or TDR probes) relies on the fact that water molecules will scatter neutrons. The amount of scattering is proportional to the amount of water present, which essentially determines the vertical distribution of the soil’s water content. It is a direct measure of soil water content.
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
COMPARISON OF METHODS FOR ESTIMATING RECHARGE –
WATER BALANCE METHODS
• A water balance links recharge and
discharge to changes in storage
(conservation of mass). A balance can be
written as a mass or volume change in time.
• In the long-term average and under neglect
of surface runoff, interflow (in-out from
adjacent aquifers) and pumping, the
difference between precipitation and
evapotranspiration is an indication of
recharge.𝑷 − 𝑬𝑻 = 𝑹
• As these quantities are both of the same magnitude and inaccurately known, theirdifference is even more inaccurate -> use long time series (identify systematic errors)
• The time-step to be used for water balance methods is important. • Niono in Mali P = 567 mm and ET = 2432 mm per year -> no recharge! • But the second ten day of August P = 45 to 175 mm in 10 days and ET = 50 to 65
mm /10 days -> recharge in August
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
COMPARISON OF METHODS FOR ESTIMATING RECHARGE –
WATER BALANCE METHODS
Soil moisture budgets
For all fluxes involved in the soil water balance, some empirical formulae exist. The
calculation from standard data is simple. For example, evaporation can be
computed by Penman’s formula and others (FAO guidelines). The usual inputs for
such a model are meteorological data from a nearby weather station, including
precipitation, radiation budget, wind speed, relative humidity, air temperature, and
soil data such as the field capacity.
River channel water balance
If recharge is confined to seepage from a river channel, the observations necessary
could in principle be very simple. Measurements of river flow are easily carried out.
If flow is measured between two points along the river, the difference will at least
convey some information about seepage and give an upper bound for recharge. If
the total flow infiltrates, the method is especially interesting.
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
COMPARISON OF METHODS FOR ESTIMATING RECHARGE –
WATER BALANCE METHODS
Water table fluctuation method
A water table rise is the clearest indicator of recharge
if all abstractions remain unchanged and atmospheric
pressure effects can be ruled out. This is a
straightforward and simple method, especially when
a full cycle of water table variation is considered. If
the storage coefficient of an aquifer is known, the
spatially interpolated water table rise can be
converted into a volume of water.
Main disadvantage: the aquifer storage coefficient should be known
• usually unknown for confined aquifers
• estimates from pumping tests are local
• density of observation boreholes in a typical arid zone is small
• water table obtained from pumped boreholes is often unreliable
• unknown amounts of “hidden” inflow/outflow from/to adjacent basins
R(tj) = Sy* DH(tj)
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
COMPARISON OF METHODS FOR ESTIMATING RECHARGE –
WATER BALANCE METHODS
River baseflow method
This method is one of the few
integrative measures of
recharge. It estimates an
integral regional value instead
of a local result. But not
feasible for ephemeral rivers.
Spring or river flow recession curves
The outflow of a catchment after the passage of the surface water wave is parametrized by
an exponential curve. The typical time constant of outflow is determined. With some
estimates on the storage volume of the drained aquifer, the recession constants allow an
estimate of recharge. It is an integrative method, but applicable only when there are
springs or perennial rivers. The catchment area must be known (physical one, not
topographical one) as well as the storage coefficient /specific yield.
Main disadvantage: long-term observations are necessary to obtain reliable results. It is
often not applicable in arid zone.
RECESSION CURVE (FROM MEYBOOM, 1991, AGU)
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
COMPARISON OF METHODS FOR ESTIMATING RECHARGE –
TRACERS METHOD
• Artificial tracers: fluorescent dyes used to measure spring flow or stream flow-> method is straightforward, the movement of the tracer is directly related to the rate of water movement
• Historical tracers: historical events which have caused the deposition of high concentration of an element at the soil surface, the rate of movement of the high concentrated tracer’s front is used to infer recharge rates
• Environmental tracers: exist naturally in the landscape and their spatial pattern or overall mass balance is used to infer recharge rates
what kind of tracer could that be?
what kind of tracer could that be?
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
HISTORICAL TRACERS
Bomb Tracers : 3H, 36Cl, 14C
1940 1950 1960 1970 1990 2000YEAR
600
400
200
0
T.U
.
1980
200
100
0
10
9ato
ms m
-2
ClH
36
3
C14
250
150
200
pm
c
100
“Society” Tracers: CFC, SF6
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
TRACERS TIMESPAN
222Rn
3H/3He
85Kr
SF6
CFC-12
CFC-113
CFC-11
39Ar
14C
81Kr
36Cl
3H
-110
-310
310
510
710
110
Age (years)
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
ENVIRONMENTAL TRACERS – THE PRINCIPLE
If we know the change in concentration over time in input, then we can infer information about water flow from changes in concentration measured at some
other location.
Concentration can be measured …
• At a point in time and space
• Through space (along a flowline)
• Through time
Three basic philosophies:
• dating methods (profiles, along flow lines)
• signature methods as a basis for mixing calculations (stable isotopes)
• flux estimation methods (mass conservation of conservative tracers)
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
ENVIRONMENTAL TRACERS – THE PRINCIPLE
• Environmental tracers provide information on the physical processes
• Example: Computed salt and water content distributions for a fallow (unvegetated) loam soil during cycles of infiltration, redistribution of soil moisture, and evaporation.
• The movement of tracers in the unsaturated zone is governed by the long-term mean soil water fluxes. The pattern of tracer distribution may therefore not correspond to momentary piezometrichead distributions and recharge.
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
ENVIRONMENTAL TRACERS – DIFFICULTIES
• Assumption piston flow -> difficult to take into account preferential flow
• Complexity in the unsaturated: hydrodynamic dispersion and diffusion
• Estimation of porosity is critical
Example: Hypothetical tracer concentration-depth profiles in the unsaturated zone after pulse application of a tracer at land surface followed by infiltration of tracer-free water
Healy, Scanlon 2012
http://unesdoc.unesco.org/images/0014/001469/146997E.pdf
• When interpreting samples from wells which mix waters of different age (travel time), or in depressionalzones, a model is needed to interpret the measured values using an assumption on travel time distribution.
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
TRACER’S METHODS: TRITIUM APPLICATION
Example: • 3H vertical profiles were measured by Solomon (1996) in a sand aquifer
in Ontario. Average porosity: 0.35. • 3H peak was found at a depth of 8.7 m below the ground.• 3H peaked in 1963
Estimate the average linear velocity and the recharge rate (recharge rate = porosity times the linear velocity)
v= dz/dt = (-8.7m) / ( 1996-1963) = -0.26 m/a
Recharge rate: R = n v = 0.09m/a
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
• Chloride is a conservative tracer: it concentrates over time or through evaporation
• Chlorine is originated in …. • Together with rainfall data, and under the
assumption of negligible runoff, recharge can
be computed:
Subsurface distribution of chloride beneath
native vegetation at sites in (a) the Murray Basin,
Australia (b) the Chihuahuan Desert, West Texas Healy, Scanlon, 2012
TRACERS METHOD - CHLORIDE APPLICATION
• Unsaturated zone chlorine concentration depthprofiles can serve as archives of past climates
𝑅 =(𝑐𝑃 ∗ 𝑃 + 𝐷)
𝑐𝐵
𝑐𝑃 : chlorine concentration in rainfall𝑃: precipitation𝐷: dry deposition of chloride𝑐𝐵: chloride concentration belowthe zero upward flux plane
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
TRACERS METHOD - CHLORINE APPLICATION
• Environmental chloride has been used to estimate impacts of changing from natural ecosystems to agricultural ecosystems, on the drainage rates through the unsaturated zone
Southern High Plains, Texas
(Scanlon et al ., 2007 )
Murray Basin, Australia (reprinted from
Journal of Hydrology , Jolly et al . ( 1989 )
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
CASE STUDIES FROM CHAD
1. Monitoring run-off, accumulation and infiltration in the arid Ennedi mountains (Northern Chad), using remote sensing
archeï
2. Identifying modern recharge in the arid region of Northern Chad: an hydrochemical baseline study of the Nubian Sandstone Aquifer System
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
0
5
10
15
20
25
30
35
40
0 1 2 3 4 5 6 7 8 9
Tota
l rai
nfa
ll m
m
1-10july
10-20 july
20-31 july
1-10august
10-20august
20-31august
1-10sept
10-20sept
July 2014 August 2014 September 2014
𝑃 = 121 𝑚𝑚
Rainfall was estimated by using FEWS-NET data (FAO’s portal)
Case study 1
36
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
Case study 1
Hydrological dynamic can be monitored by remote sensing (LandSat8)NDWI index18 august 2014
3 september 2014
6 november 2014
37
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
Evapotranspiration was estimated by calculating a SurfaceEnergy Balance from LandSat8 images (30 m resolution)
18.08.2014 05.10.2014 22.11.2014
𝐸𝑇 = 88 𝑚𝑚
Case study 1
𝜆𝐸 = 𝑅𝑛 − 𝐺 − 𝐻
38
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
0
10
20
30
40
50
60
70
80
20.07.2014 09.08.2014 29.08.2014 18.09.2014 08.10.2014 28.10.2014 17.11.2014 07.12.2014
Cu
mu
late
dre
sid
ual
(mm
)
05
10152025303540
1-1
0 ju
ly 2
01
4
11
-20
july
20
14
21
-31
july
20
14
1-1
0 a
ugu
st 2
01
4
11
-20
au
gust
20
14
21
-31
au
gust
20
14
1-1
0 s
epte
mb
er2
01
4
11
-20
sep
tem
ber
20
14
rain
fall
(mm
)
𝑃 −𝐸𝑇 = 33 𝑚𝑚
0
10
20
30
40
ET (
mm
)
We calculate the residual
Case study 1
𝑃 = 121 𝑚𝑚 𝐸𝑇 = 88 𝑚𝑚
39
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
Case study 1
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
22.11.2013 11.01.2014 02.03.2014 21.04.2014 10.06.2014 30.07.2014 18.09.2014 07.11.2014 27.12.2014
chan
ge t
ota
l wat
er
sto
rage
(m
m)
GRACE
Change in Total Water Storage ∆TWS (GRACE satellite, resolution 110 km)
SnWS = snow-water storage
RESS = reservoir storage
SMS = soil moisture storage
GWS = groundwater storage
∆𝑇𝑊𝑆 = ∆𝑆𝑛𝑊𝑆 + ∆𝑅𝐸𝑆𝑆 + ∆𝑆𝑀𝑆 + ∆𝐺𝑊𝑆
Lakes of Ounianga, N Chad
40
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
Case study 2
Stable isotopes were measured and compared to the spatial distribution of rainfall (FEWS-NET data)
Ennedi
Tibesti
41
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
Case study 2Groundwater flow conceptual model based on water table elevation of 150 water points in an area of 80’000 km2. Use of hydrochemical and isotopic patterns to formulate hypothesis.
Origin of the Ounianga Lakes
42
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
HOW DO I GET STARTED
First step:
• Gather daily meteorological data for the area under consideration, if you can. Consider using remote sensing data.
• Calculate potential precipitation recharge for one or ten-day periods usingprecipitation and potential evapotranspiration rates
𝑅 = 𝑃 − 𝐸𝑇𝑝
-> will reveal the temporal variability and the minimum rate of potentialprecipitation recharge
Second step:
• Collate all information available of the geology, surface and groundwaterhydrology, climate, topography, pedology and vegetation
-> construct the conceptual model of the precipitation recharge mechanisms, taking into account localized recharge, occurrence of
preferential flow paths, characteristics of the unsaturated zone
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
Third step:
• Select a method appropriate to the hydrogeological conditions and the final aim(e.g. water management)
• In arid and remote areas, coupling tracer’s methods, which generally do not necessitate repeated field investigations, and other indirect methods (water balance, darcyan methods, numerical modelling) holds much potential. It can beadapted to different timescales, therefore their application can be multiple.
Fourth step:
• Long-term monitoring programs
…AND THEN…
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
PROBLEMS OF DATA AVAILABILITY
• The scarcity of data is a great problem in arid zone modelling
• In some cases data are available but are not published
• Acquiring of such data might be of high cost and is often not seen as a priority
• This situation is unlikely to change
• But remote sensing data are helping filling the gap
• For morphological and hydrological analysis: SRTM: 80% of the land surface
mapped, 90% confidence interval of elevation: 16 m
• LandSat or other multispectral images (from 1972)
• Analysis of multi-components through a GIS interface
• Example from Chad: the ResEau project
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
REMOTE SENSING PRODUCTS
https://lta.cr.usgs.gov/get_data/
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
EXTERNAL WATER SOURCERECHARGE COMPLETE
Mixed Zone
InjectedWater Level
INJECTEDWATER
Higher water level and greatly
improved groundwater salinity
Mixed Zone
Progressive PumpingWater Level
INJECTEDWATER
Pumping gradually lowers groundwater
level to original water table level
INJECTED WATER or MIXEDWATER FOR IRRIGATION
Artificial storage and recovery
Watch the movie: https://www.youtube.com/watch?v=NUM9OAKjcyA
47
CHYN-UNINE Recharge in Arid and Semi-Arid Regions 06.09.2018
THANK YOU FOR YOUR ATTENTION!
Marie-Louise Vogt
Centre d’Hydrogéologie et Géothermie
Université de Neuchâtel
Rue Emile-Argand 11
CH-2000 Neuchâtel
www.unine.ch