Hydrology of Inland Flooding  Stream Gauges  Hydrologic Forecast Process  Forecast Considerations  Forecast Hydrographs 3-1

Stream Gauges

 Manual gages (wire weight or staff) Low cost By definition, requires trained human observer Not usually available at night  Automated gages Installation costs + Maintenance costs Available 24/7

Hydrologic Forecast Process  Modeling how much rain gets into the river (Rainfall to Runoff)  Modeling how fast water gets to the river gage (Unit Hydrograph)  Modeling how fast upstream water arrives at the gage (Routing)  Translating water volume into water height (Rating)

Rainfall to Runoff Modeling

T=0 hours DIRECT SURFACE INTERFLOW BASEFLOW 6 hours12 hours24 hours18 hours30 hours

Unit Hydrograph

Routing Time Gage Height

Meramec River near Steelville, MO

Hickory Creek near Bluff City, IL

River Forecasts – How are they created? Observed Precipitation Observed Precipitation Future Precipitation Future Precipitation Soil Model Rainfall to Runoff Soil Model Rainfall to Runoff Local Basin Rating Curve Flow to Stage Rating Curve Flow to Stage Unit Hydrograph Runoff to Flow Unit Hydrograph Runoff to Flow Upstream Flow Upstream River Gage Basin Local Flow Total Flow (cfs) Total Flow (cfs) Forecaster Modification Forecaster Modification Forecast To Public Forecast To Public Forecast River Gage

Forecast Considerations  Ground State (How dry is it?)  Past Model Performances  Rainfall (Gage-based or Radar-based?)  Rainfall Variability Space Time

Rainfall Variability

Forecast Hydrographs  Model Hydrographs  Forecast Hydrographs

Model Hydrograph

Summary  Which river gauge requires a stilling well? A. Acoustic sonar B. Float type C. Pressure transducer

 What type of runoff causes the river to rise the quickest? A. Direct runoff B. Interflow C. Baseflow

 What hydrologic method takes basin-wide runoff and converts it to flow (discharge) over a period of time at the river gauge? A. Rainfall to Runoff model B. Unit Hydrograph C. Routing model D. Rating curve