The FEWS Flood Risk Monitoring Model From Rain to Rivers Tanya Hoogerwerf Thursday, February 22, 2001

FEWS Model Provides a continuous simulation of stream flow, on a daily time step, for nearly 3,000 basins on the African continent. Rainfall/runoff simulation model containing… –a soil water accounting module that produces surface and sub-surface runoff for each sub-basin –an upland headwater basins routing module – and a major river routing module.

Runoff Producing Mechanisms Surface runoff due to precipitation excess (including direct runoff from impermeable areas of the basin) Rapid Subsurface Flow (interflow), and Base Flow

Soil Water Accounting Module (SAC-SMA) Revisited Baseflow Active Layer FEWS: Active Zone (2 layers) & Groundwater Zone (1 layer)

Runoff Calculations The HYDRO1K data provide basin boundaries and stream networks that form the spatial framework of the model. The FAO soil map provides characterization of the hydraulic properties of the earth's surface that are required to compute the water balance within a basin. The NOAA RFE provide the estimates of gross precipitation input to each basin.

Total Channel Inflow (SAC-SMA) uT = Channel Inflow from SWC= Surface Runoff + Base Flow Runoff Surface Runoff = f(Precipitation, Soil Water Content, SR Gen.) Base Flow Runoff = f(BF Recession Rate, SWC, BF Lost to Aquifers) Water Balance Relationship for Each Reach: dSidt = U i-1 + p i *uT – U i S=Water Volume P i = Fraction of Total Water Inflow Corresponding to Reach i U i = Reach i U i-1 = Upstream Inflow from Reach i-1

Time of Concentration Grid Slope, flow direction, and flow accumulation grids of the HYDRO1K Manning equation for flow in an open channel Units: 1/10 day

Rainfall NOAA has produced RFE images (Herman et al., 1997) on a dekadal (10-day) time step Basin Excess Rainfall Maps (BERM) Produced

Output Mozambique Flood Information Stream Flow Model Flood Risk Map Page (select Pfafstetter Basin)

References USGS/EROS Data Center Riverside Technology Real-Time Prediction for Flood Warning and Management- Georgakakos 1995 Coupled Rainfall- Flow Forecasting Models- Georgakakos