1. FLOOD SERVICE CAPACITY BUILDING
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

2. Outline Background and Objectives
Structure of Capacity building material
The Flood Service System
Vienna Office

3. BACKGROUND TO FLOOD SERVICE
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

4. Why monitor floods?

5. Flood Service Objectives
The flood service aims to provide earth observation products for monitoring the status before, during and after a flood event.
This will contribute to effective land use and disaster management planning and policy making and improve security for people in areas affected by floods.

6. Before the flood
The aim is to contribute to prevention of and preparedness to floods. This component includes the following sub-elements:
Flood risk models- to determine flood-prone and flood safe areas based on historical earth observation data.
Flood Forecasting system – To warn the countries in the likely event of floods.

7. During the flood
This component aims to provide Near Real-Time information on the extent of flood events, including map products showing flooded areas.

8. After the flood
To guide disaster relief planning and management during and after a flood event through flood damage assessments, including flooded area maps overlaid with human assets.

9. CAPACITY BUILDING MATERIAL
STRUCTURE
CAPACITY BUILDING MATERIAL
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

10. Outline Flood Concepts Flood Monitoring Flood Forecasting
Flood Hazard Modelling
Flood Damage Assessment
Flood Reporting
Vienna Office

11. Concepts
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

12. Types of floods
Flash floods- are often the result of heavy rains of short duration.
Fluvial flooding/riverine- occurs when rivers overflow their banks as a result of sustained or intense rainfall.
Coastal flooding is caused by extreme tidal conditions including high tides, storm surges and tsunamis.

13. Response to Floods Structural/Engineering Approaches
Non-structural/ Vulnerability reduction
Early warning systems

14. Early Warning systems

15. FLOOD MONITORING
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

16. Remote sensing floods Landsat 8 Envisat SORCE Aura/Aqua/Terra Sage
Sentinel 1
QuikScat
IKONOS
CBERS
SeaWiFS
SPOT 4, 5
SPIN-2
SeaWinds
SAC-D/Aquarius
TRMM
Orbview 2, 3
DMC
ACRIMSAT
EROS A1
ERBS
Radarsat
ALOS
TerraSAR-X/Tandem-X
Toms-EP
QuickBird
Grace
SAC-C
Jason
Landsat 7
UARS
COSMO-SkyMed
© GEO Secretariat

17. Remote sensing floods
Traditionally, flooding has been estimated by measuring water levels at gauging stations.
Although these monitoring networks provide good historical data for flooding, it lacks spatial information due to the limited number of stations over large areas.

18. Remote sensing floods
Remote sensing is valuable in flood monitoring because of its unique capabilities to provide
comprehensive,
synoptic and
multi-temporal coverage of very large areas at regular interval and with quick turn around time.

19. Remote sensing floods Remote sensing provides information on
flood inundated and drainage congested areas.
extent of damages to crops, structures etc.
river configuration, silt deposits and vulnerable areas of bank erosion.
watershed characteristics and land cover/land use.
Meteorological data

20. Remote sensing floods
Remote sensing approaches used in flood monitoring include optical remote sensing and synthetic aperture radar (SAR).
Optical remote sensing is often useful in cloud free conditions for monitoring progression of a flood or the inundated area.
For example, progression of the Katima Mulilo Namibia flood of 2004 based on MODIS TERRA and flood extent in the Shire Basin

21. Shire Example 2015 Flood

22. Katima Mulilo Namibia flood of 2004
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

36. THANK YOU
This presentation has been prepared with the financial assistance of the European Union. The contents are the sole responsibility of MESA SADC THEMA and can under no circumstance be regarded as reflecting the position of the European Union

37. FLOOD FORECASTING
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

38. Flood Forecasting
Forecasting of floods enable early warning to be issued to communities likely to be affected by the flood.
Flood forecasting is an effective non-structural flood control measure.

39. Flood Forecasting
Several methods have been developed to allow forecasting of floods BUT
with the advancement of remote sensing and GIS, near real time flood forecasting is now becoming a reality.

40. Hydrological model Types
CHARACTERISTICS
Lumped
Basin treated as a single unit for inputting data and calculating runoff.
basin response is evaluated at the outlet, parameter estimates of the model do not vary spatially in the basin
Semi-distributed
A basin is broken down into smaller sub-basins
Sub-basins estimate used to determine streamflow for the larger basin at the
Distributed
Basin characteristics determined within each cell i.e streamflow estimates
Parameters of distributed models are fully allowed to vary in space

41. Flood Forecasting/Modelling
Has two components
hydrological model and
hydraulic model

42. Hydrological Modelling
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

43. Hydrological model
The aim is to transform rainfall into water available for runoff after accounting for the processes of evaporation, interception and infiltration.

44. Water available for runoff

45. Soil Hydrological Group

46. Curve Number Determination

47. Water available for runoff
The rainfall-runoff equation used by the SCS for estimating depth of direct runoff Q from rainfall is
P =precipitation
S= potential maximum retention or watershed storage (mm)

48. SCS-CN: Estimating runoff
The parameter S is related to CN by
CN is the curve number, which depends on land use, hydrologic soil group, hydrologic condition and antecedent moisture condition.

49. Hydraulic modelling
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

50. Hydraulic models
Hydraulic models are used for channel routing to calculate the travel time of the flood wave and its attenuation.

51. Hydraulic modelling stages
Water available for runoff

52. Hydraulic Radius Flow accumulation value Hydraulic radius <123457
0.002
0.005
0.01
0.02
>493827
0.05

53. Water Velocity
The flow velocity of the runoff per pixel is then determined using the Manning's equation:
where V = velocity, Rh = hydraulic radius, S = slope in percent and N = Manning's constant.
The Manning's N is a value between zero and one.

54. Manning’s N

55. Time spent/m
The time spent per metre (t) at each point within the watershed is then determined by inverting the flow velocity (V)

56. Time to outlet/Isochrones
Isochrones/ the time needed for each pixel's runoff to reach the outlet (Tp) is sum of product of(ti) and flow path length (li).

57. Shashe Zimbabwe-Botswana 10 March 2016

58. THANK YOU
This presentation has been prepared with the financial assistance of the European Union. The contents are the sole responsibility of MESA SADC THEMA and can under no circumstance be regarded as reflecting the position of the European Union

59. FLOOD HAZARD
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

60. Flood Hazard
A flood hazard refers to the probability that a flood of certain magnitude will occur at a certain location within a specific period of time.
Flood hazard mapping is critical for determining flood safe areas and areas that are vulnerable to flooding.

61. Flood Hazard
Flood hazard maps have been developed based on the recurrence interval determined from data on river discharge of previous floods.
The boundary of the 100-year flood is commonly used in floodplain assessments to identify areas where the risk of flooding is significant.

62. Flood hazard assessment
Several approaches are utilized in flood hazard assessments and these include:
hydrological modeling
field and statistical approaches
remote sensing + DEM

63. Field and statistical approaches
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

64. Field and statistical approaches
Field data is collected on previously flooded and non-flooded areas.
The location of sites that were flooded or not flooded is determined using the Global Positioning System (GPS) this defines the flood condition.

65. Flood hazard mapping

66. Height above channel base
Height above channel base is characteristic for each recurrence period i.e. 10 yr, 50 yr, 100 yr.
For example for 100 yr it can be 4 m while for 2 year it can be 50 cm, i.e. within channel

67. Height above channel base
Height above channel base is determined by subtracting ground surface from channel base.

68. Height above channel base
A relationship is then determined between flood presence / absence data with height above channel base using logistic regression.
Maps are then constructed in a GIS using the derived logistic regression equation to show the probability of an area being inundated with water for each flood frequency.

69. Hydrological models

70. Flooding condition

71. Flood Hazard

72. Flood hazard Mapping: 2 year

73. Flood hazard Mapping: 10 year

74. Flood hazard Mapping: 20 year

75. Flood hazard Mapping: 50 year

76. Flood hazard Mapping: 100 year

77. Flood hazard zones: 100 year

78. SADC Height above channel

79. SADC Height above channel

80. Flood Risk
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

81. Flood Risk
A flood risk is the probability of harmful consequences or expected loss of lives, people injured, property, livelihoods, economic activity disrupted or environment damaged resulting from interactions between the flood hazard and vulnerable conditions.
Risk is the probability of loss

82. Land cover/use (weighted)
Quantifying Risk
Flood hazard
Land cover/use (weighted)
Flood Risk map

83. FLOOD DAMAGE ASSESSMENT
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

84. Flood Damage
Flood damage is the total or partial physical destruction of physical assets as a result of contact with flood waters.
Damage occurs during as well as after the flood event
The monetary value of damage can also be assessed.

85. Area of farmland affected/number of settlements affected
Damage assessment
Flood extent/depth
Land cover/use
Area of farmland affected/number of settlements affected

86. Area flooded

87. Homesteads 1 2 3

88. Flooded homesteads 1 2 3

89. FLOOD REPORTING
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

90. Outline Reporting before the flood Reporting during the flood
Reporting after the flood
Vienna Office

91. THANK YOU
This presentation has been prepared with the financial assistance of the European Union. The contents are the sole responsibility of MESA SADC THEMA and can under no circumstance be regarded as reflecting the position of the European Union

92. PRODUCTS IN THE FLOOD SERVICE
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

93. Products FPL01: Soil saturate hydraulic conductivity maps
FLP02: Friction Map
FLP03: DEM for SADC
FLP04: River Network for SADC
FLP05: Flow Direction for SADC
FLP06: Flow Accumulation for SADC
FLP07: Land Use map SADC

94. Products FLP08: Height above channel FLP09: Distance to channel
FLP10: Map of 3hr intensity rainfall
FLP11: Discharge Data for hydrological model (auto-calibration)
FLP12: Flood Conditions Water Extent
FLP13:GFS Precipitation

95. Products FLP14: Flood Hazard Maps FLP15: Small water bodies
FLP 16: Southern Africa Seasonal rainfall Forecasts

96. River networks

97. Rainfall

98. Infrastructure

99. Quick Demonstration
University of Zimbabwe, Department of Geography and Environmental Science: GIS and Earth Observation Centre of Excellence

100. THANK YOU
This presentation has been prepared with the financial assistance of the European Union. The contents are the sole responsibility of MESA SADC THEMA and can under no circumstance be regarded as reflecting the position of the European Union