Estimating flood hydrographs for Arkansas streams

Flood hydrographs are needed for the design of many highway drainage structures and embankments and flood water storage structures. A dimensionless hydrograph is presented for Arkansas streams having drainage areas < 600 sq mi. This dimensionless hydrograph can be used with peak discharge and equivalent lagtime to determine flood hydrographs at ungaged sites on rural and urban streams in Arkansas. Multiple regression analysis was used to define relations between equivalent lagtime and basin, climatic, and hydrologic characteristics. Data collected on 450 storms at 9 gaging stations were used in the analysis. The regression analysis indicated that drainage area and 100-year discharge are significant parameters for estimating equivalent lagtime. The standard error of the regression equation is +/-38 %. The equation was tested for accuracy, bias, and sensitivity. An equation is presented for computing the volume of flood runoff when the peak discharge, equivalent lagtime, and drainage area are known. In addition, a hydrograph-width relation is presented for estimating the length of time that a specific discharge will be exceeded. (Lantz-PTT)