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Bankfull Regional Curve

Sugar Creek Case Study Regional Curve
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BANKFULL PROPERTIES - INTRODUCTION

Bankfull discharge is commonly thought of as the flow that fills the channel up to the top of banks, prior to flooding. For undisturbed, poised streams with wide floodplains, this definition would be correct. However a majority of streams have degraded or down cut, through natural processes or induced by civilization, where the discharge to fill the stream to the top of banks is a misnomer of bankfull discharge.

In 1978, Dunne and Leopold provided a generally accepted definition of bankfull discharge: The bankfull stage corresponds to the discharge at which channel maintenance is the most effective, that is, the discharge at which moving sediment, forming or removing bars, forming or changing bends and meanders, and generally doing work that results in the average morphologic characteristics of channels.

The bankfull discharge does not transport the most sediments at one time, but cumulatively, it is the most effective discharge at transporting sediments over time. The bankfull discharge is usually exceeded twice every three years.

Determining proper bankfull width, depth, and cross sectional area for a given size drainage area was a top priority for the Sugar Creek's Study Team. A regional curve of bankfull dimensions plotted versus drainage area would serve as one critical design element to realigning a disturbed system back to a poised or properly functioning system.

Selection of United States Geological Survey (USGS) gages for the regional curve were based on the following criteria:

  • Gages in the same physiographic region as Sugar Creek, i.e. the Red and nearby Canadian River Basins
  • Ten years minimum of gage record, (20+ years preferred)
  • Gaged drainage area represents no or a minimum amount of, control or regulation
  • History of stable rating curves, i.e. the gaged stream was not degrading during the gage record
  • Drainage areas ranging up to 200 square miles

Sugar Creek Watershed Study - Bankfull Discharges
(1.5 year probable exceedance estimates)

Sugar Creek Watershed Study - Bankfull Discharges
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