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Monitoring Small Reservoirs in the Volta Basin of Ghana
1. A Partner
of
Monitoring Small Reservoirs in the
Volta Basin of Ghana
Frank Annor, Nick van de Giesen, Tom Bogaard & Dirk Eilander
(f.o.annor@tudelft.nl)
CPWF Scientific Workshop , 17-19 September 2013, Ouagadougou, Burkina Faso
2. Andes • Ganges • Limpopo • Mekong • Nile • Volta
Content
1. Main message & Background
2. Methodology
3. Preliminary results & Discussions
4. Outlook
5. 5
The Volta River System
≈400,000 Km2
UER = 8,570 km2
RF 500 (N)-1100 (S)mm/yr
6. Andes • Ganges • Limpopo • Mekong • Nile • Volta
How can we bridge the poverty gap?
7. Andes • Ganges • Limpopo • Mekong • Nile • Volta
Small Reservoirs – multiple uses
Farming
Rain-fed – not enough (1970s -1980s
Drought!)
8. 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
9. Andes • Ganges • Limpopo • Mekong • Nile • Volta
Monitoring network
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
1,244
18,780
24,927
11,359
23,033
62,010
6,309
27,993
7,052
Area per WMO Station in km²
Data: Deutscher Wetterdienst (2008)
13. Monitoring - Satellite
Evaporation
SN Satellite Data
Spatial
resolution
Geo-biophysical
Variables to be
retrieved Dates
Data
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
3
Landsat 7 ETM+
(8) 30m, 60m
LAI, LST, NDVI,
Emissivity, Albedo Mar-07 to Mar 2012; 2013 √X ESA/USGS
4ASTER 15, 30,90m
LAI, 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/USGS
2Radarsat-2 < 7m Nov-12 to Present √ CSA
3
ENVISAT
(ASAR) 30m Mar-07 to Mar 2012 √ ESA
4ALOS 7m ? √ JAXA
5SPOT 10m ? √ ESA
14. Andes • Ganges • Limpopo • Mekong • Nile • Volta
Issues - RS Evaporation estimates
L - Avg. RMSE of 50Wm-2 & 15 – 30% RE
Physical and Analytical methods are not better than
empirical and statistical approaches
Empirical methods are limited by in-situ training data
Diurnal variation of evaporation vrs instantaneous
measurements with RS (Bowen Ration & evaporative
fraction)
Temporal & Spatial Scaling issues (extrapolation, gap
filling & data fusion) + clouds
Surface energy models (SEBAL, SEBS etc.)
Kalma et al. (2008) & Farah et al. (2004)
15. Andes • Ganges • Limpopo • Mekong • Nile • Volta
Base Map & Radar monitoring
Landsat SPOT
ASAR, ALOS & Radarsat-2
Radar MonitoringOptical – base map
Growing MLC - automation
NIR & visible wavelengths Intensity - Roughness & Polarisation
18. RADARSAT-2 SAR imagery
SR154, Pauli decomposition
RGB Composition:
R: Single Bounce
G: Volume Scattering
B: Double Bounce
RGB composition RGB comp [3x3 window]
Single Bounce
A
Double bounce
C
Volume Scattering
B
19. 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
21. 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
30. Andes • Ganges • Limpopo • Mekong • Nile • Volta
Outlook
Evaporation estimates (RS)
Comparison with Flux measurements
Scale effects & boundary conditions of evaporation from SR
Design of reservoirs for optimum storage in dry season?
31. Andes • Ganges • Limpopo • Mekong • Nile • Volta
Thank you!
www.smallreservoirs.org
Editor's Notes
Small reservoirs are by definition 1~100haIn semi-arid africa houndreds of sr dot the landscapeOnly source of water in dry season for many small livelyhoodsMultipurpose use (cattle, bathing, irrigation etc)Why do we want to monitor small reservoirs?-In order to learn more about the hydrology-Their impact on river basin scale
Focus on step 3, delineation algorithmApproach:Development basic algorithmEvaluate polarization diversity with basic algorithmImprove algorithmWhy evaluation polarization diversity:To analyze which polarization modes are less affected by Bragg scattering and gives best contrast