Stream Design Curves

Stream Restoration Design Curves

dropcap blurb for web pageStream design curves are created by analyzing the morphology of a statistically significant number of stable streams and plotting the data. The data gathered, typically bankfull width, bankfull height, and sinuosity, is then plotted against drainage area to demonstrate the correlation between the various channel characteristics and the hydrology of the region. The trend line can then be used by designers and managers to provide initial channel measurements for a stream restoration project.

The development and use of regional curves by fluvial geomorphologists began in the 1950’s by Luna Leopold. This work  indicated that it is common for there to be strong correlations between channel shapes, discharges and drainage areas. After Leopold published design curves for the San Francisco Bay area in 1978, it became clear that this region needed more data at the sub-regional level. A number of hydrogeomorphologists in the bay area have since worked to improve the accuracy and precision at the sub-regional scale.

The user of a regional curve, when used appropriately, can acquire  meaningful initial estimates of the average channel shapes for  streams in that region based on drainage area.  This is useful to the restoration designer or public works official who wants to know  if a  stream reach of concern has a cross-sectional area which is close to, or far off from the the regional average. This comparison can provide insight to the stability of the reach. “Stability” in this context  means that the  channel is not excessively eroding or depositing sediment but has dynamic meandering, sediment transport and erosion to build pools, riffles, step-pools and other instream complexity. The regional curves can be very helpful in determining “equilibrium” channel shapes for stream reaches for which there  are not nearby reference reaches in good condition  to help inform a stream channel restoration .

If these design curves are used to inform a channel design, it is necessary to incorporate additional information into determining an equilibrium channel shape.  These  design tools can include the more complex dimensionless rating curves, and  computations of effective discharges which form the channels. Some stream channel  types are not conducive to being represented by regional curves such as streams located in alluvial fans, channels just upstream of marshes, or channels in steep areas of a watershed.[toggle_box] [toggle_item title=”Background” active=”false”]In 1978 a regional curve was published for the Bay Area by Dunne and Leopold and included information from most of the Bay Area counties. Because the Bay Area has so many different micro climates, it is necessary to develop curves which represent these different sub-regional environments to ensure designers have the most applicable data available. For this reason the EPA and SFEP are supporting the development of regional curves which represent the conditions found in the different sub-regions of the Bay. Developed urban environments that have not experienced much land use change in the past few decades can benefit  from  developing curves representing a built out urban equilibrium. Areas  in process of undergoing land use changes are not good candidates for developing the curves.[/toggle_item] [/toggle_box] [tab] [tab_item title=”Design Resources”]

Design Primer by Anne Riley (San Francisco Bay Water Quality Control Board)

Original San Francisco Bay Regional Curve

[/tab_item] [tab_item title=”North Bay”] [/tab_item] [tab_item title=”East Bay”] [/tab_item] [tab_item title=”SF Peninsula”]
  • San Francsico
  • San Mateo – Currently being developed (expected in 2016)
[/tab_item] [tab_item title=”South Bay”]