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

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

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

Why monitor floods?

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.

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.

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

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.

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

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

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

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.

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

Early Warning systems

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

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

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.

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.

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

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

Shire Example 2015 Flood

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

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

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

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.

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.

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

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

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

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

Water available for runoff

Soil Hydrological Group

Curve Number Determination

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)

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.

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

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

Hydraulic modelling stages Water available for runoff

Hydraulic Radius Flow accumulation value Hydraulic radius <123457 0.002 123457-246914 0.005 246915-370370 0.01 370371-493827 0.02 >493827 0.05

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.

Manning’s N

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

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).

Shashe Zimbabwe-Botswana 10 March 2016

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

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

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.

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.

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

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

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.

Flood hazard mapping

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

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

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.

Hydrological models

Flooding condition

Flood Hazard

Flood hazard Mapping: 2 year

Flood hazard Mapping: 10 year

Flood hazard Mapping: 20 year

Flood hazard Mapping: 50 year

Flood hazard Mapping: 100 year

Flood hazard zones: 100 year

SADC Height above channel

SADC Height above channel

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

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

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

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

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.

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

Area flooded

Homesteads 1 2 3

Flooded homesteads 1 2 3

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

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

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

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

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

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

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

River networks

Rainfall

Infrastructure

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

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