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Monitoring Small Reservoirs in the Volta Basin of Ghana
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Transcript of Monitoring Small Reservoirs in the Volta Basin of Ghana
A Partner of
Monitoring Small Reservoirs in the Volta Basin of Ghana
Frank Annor, Nick van de Giesen, Tom Bogaard & Dirk Eilander([email protected])
CPWF Scientific Workshop , 17-19 September 2013, Ouagadougou, Burkina Faso
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Content1. Main message & Background2. Methodology3. Preliminary results & Discussions4. Outlook
MAIN MESSAGE & BACKGROUND
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Main message
© pubs.usgs.gov
12mm/day
9mm/day
1.4mm/dayend of June
Feb. - March
A Partner of
5
The Volta River System
≈400,000 Km2
UER = 8,570 km2
RF 500 (N)-1100 (S)mm/yr
Andes • Ganges • Limpopo • Mekong • Nile • Volta
How can we bridge the poverty gap?
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Small Reservoirs – multiple usesFarming Rain-fed – not enough (1970s -1980s
Drought!)
Andes • Ganges • Limpopo • Mekong • Nile • Volta
What are the issues with SR?
Lack of adequate storage facilities (design & capacity problems!) & productive use of existing facilities
Large (?) Evaporation losses
Sedimentation not really a problem – 3400t/year
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Monitoring network
German
yBenin
Burkina F
aso
Ghana
Ivory
Coast
MaliTogo
Nigeria
South
Africa
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
1,244
18,78024,927
11,359
23,033
62,010
6,309
27,993
7,052
Area per WMO Station in km²
Data: Deutscher Wetterdienst (2008)
Monitoring network - TAHMO
METHODS
A Partner of
Methodology
Satellite & GPS
Ground Measurements
Reservoir Masks
BEAMILWIS, ERDAS WS + ECS Isotopes
variables
Evap – EBM(heat fluxes, Ef) Evap - ECS Evap - WB
Satellite Imagery
Retrieval of
variables
A Partner of
Monitoring - SatelliteEvaporation
SN Satellite DataSpatial
resolution
Geo-biophysical Variables to be
retrieved DatesData
availability Source
1MERIS 260m
LST & NDVI, Emissivity, Albedo
Mar-11 to Mar 2012 √ ESA
2AATSR 1km
LST & NDVI, Emissivity
Mar-11 to Mar 2012 √ ESA
3Landsat 7 ETM+ (8) 30m, 60m
LAI, LST, NDVI, Emissivity, Albedo Mar-07 to Mar 2012; 2013 √X ESA/USGS
4ASTER 15, 30,90mLAI, LST, EVI, Emissivity, Albedo Mar-11 to Mar 2012 √ USGS (NASA)
5Sentinel - 2 20m (?)LAI, LST, NDVI, Emissivity ? X ESA
Water Mask and Water Monitoring
1Landsat 30m Mar-92 to Mar 2012 √ ESA/USGS2Radarsat-2 < 7m Nov-12 to Present √ CSA3ENVISAT (ASAR) 30m Mar-07 to Mar 2012 √ ESA4ALOS 7m ? √ JAXA5SPOT 10m ? √ ESA
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Issues - RS Evaporation estimatesL - Avg. RMSE of 50Wm-2 & 15 – 30% REPhysical and Analytical methods are not better than empirical and statistical approachesEmpirical methods are limited by in-situ training dataDiurnal variation of evaporation vrs instantaneous measurements with RS (Bowen Ration & evaporative fraction)Temporal & Spatial Scaling issues (extrapolation, gap filling & data fusion) + cloudsSurface energy models (SEBAL, SEBS etc.)
Kalma et al. (2008) & Farah et al. (2004)
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Base Map & Radar monitoring
Landsat SPOT
ASAR, ALOS & Radarsat-2
Radar Monitoring
Optical – base map
Growing MLC - automation
NIR & visible wavelengths Intensity - Roughness & Polarisation
Fieldwork
1-3 3-5 5-7 7-9 9-11 11-13
13-15
15-17
17-19
>1902468
1012
Area [ha]
FieldworkSR154
SR120
RADARSAT-2 SAR imagerySR154, Pauli decomposition
RGB Composition:
R: Single BounceG: Volume Scattering B: Double BounceRGB composition RGB comp [3x3 window]
Single Bounce
A
Double bounce
C
Volume Scattering
B
Andes • Ganges • Limpopo • Mekong • Nile • Volta
One temporal prior for previous and two for subsequent classifications. Subsequent is dependent on rain / dry season.
Based on 3 pix moving average
Growing way of filtering unclassified pixels/ removing water and land ‘islands’
SR Delineation
WOIS
20
Storage - Bathymetry
0
1
2
3
4
5
6
0
10,000
20,000
30,000
40,000
50,000
Dep
th (m
)
Are
a (m
2 )
Volume (m3)
Area Depth
Volume = 0.00857 x Area1.4367 m3
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Time Series of SR – Mass balance
21
Small Reservoir Storage (S)
Seepage
EvaporationRainfall
IrrigationRunoff
≈ 0 ?
Onset of the dry season - Nov
PRELIMINARY RESULTS & DISCUSSIONS
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Time series of SR …1
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Time series of SR …2
26 Reservoirs
Weather Station @ Binaba (Telemetry)
Measurements (ECS + WS + L) Instrumentation
41230 41238 41246 41254 41262 41270 41278 41286 41294 41302 41310 41318 41326 41334 41342-160
-140
-120
-100
-80
-60
-40
-20
0
20
MW_Upstream MW_MidstreamMW_Downstream Lake
Water Level Fluctuations
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Water Balance of SR
27
Isotopes
Evaporation
11/11/2
012
11/18/2
012
11/25/2
012
12/2/2
012
12/9/2
012
12/16/2
012
12/23/2
012
12/30/2
012
1/6/2
013
1/13/2
013
1/20/2
013
1/27/2
013
2/3/2
013
2/10/2
013
2/17/2
013
2/24/2
013
3/3/2
013
3/10/2
013
3/17/2
013
3/24/2
013
3/31/2
013
4/7/2
013
4/14/2
013
4/21/2
013
4/28/2
013
5/5/2
013
5/12/2
013
5/19/2
013
5/26/2
013
6/2/2
013
6/9/2
013
6/16/2
013
6/23/2
013
6/30/2
0130
5
10
15
20
25
30
35
40
0
1
2
3
4Evaporation Temperature (atm) Wind Speed
Date
Evap
orati
on (
mm
/day
)Te
mpe
ratu
re (o
C)
Win
d Sp
eed
(m/s
)
Avg - 9mm/dayMin - 1.4mm/dayMax - 12mm/day
OUTLOOK
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Outlook
Evaporation estimates (RS)Comparison with Flux measurementsScale effects & boundary conditions of evaporation from SRDesign of reservoirs for optimum storage in dry season?
Andes • Ganges • Limpopo • Mekong • Nile • Volta
Thank you!
www.smallreservoirs.org