Bankfull Regional Curves for North and Northwest Florida Streams¹

Abstract

Regional curves, which relate bankfull channel dimensions and discharge to watershed drainage area, are developed to aid in identifying the bankfull stage in ungaged watersheds, and estimating the bankfull discharge and dimensions for river studies and natural channel design applications. This study assessed 26 stable stream reaches in two hydro‐physiographic regions of the Florida Coastal Plain: the Northwest Florida Coastal Plain (NWFCP) and the North Florida Coastal Plain (NFCP). Data from stream reaches in Georgia and Alabama were also used to develop the Florida regional curves, since they are located in the same hydro‐physiographic region. Reaches were selected based on the presence of U.S. Geological Survey gage stations and indicators of limited watershed development (e.g., <10% impervious surface). Analyses were conducted to determine bankfull channel dimensions, bankfull discharge, average channel slope, and Rosgen stream classification. Based on these data, significant relationships were found between bankfull cross‐sectional area, width, mean depth, and discharge as a function of drainage area for both regions. Data from this study suggested that bankfull discharges and channel dimensions were larger from NWFCP streams than from Coastal Plain streams in North Carolina and Maryland. Bankfull discharges were similar between NFCP and Georgia coastal plain streams; therefore, the data were combined into one regional curve. In addition, the data were stratified by Rosgen stream type. This stratification strengthened the relationships of bankfull width and mean depth as a function of drainage area.

Development of Regional Curves for Hydrologic Landscape Regions (HLR) in the Contiguous United States

“…Developing a stream restoration design, such as through natural channel design techniques, is an iterative process that often begins by identifying the appropriate bankfull discharge and bankfull channel dimensions such as cross‐sectional area, width, and mean depth in the riffles, predominately in perennial streams, with the aid of regional curves (Doll et al ., ; Hey, ; USDA‐NRCS, ). Regional curves relate these bankfull channel characteristics ( i.e ., dependent variable) to drainage area ( i.e ., independent variable) and can provide designers with (1) tools to help identify bankfull elevation in the field such as when bankfull indicators are absent or infrequent (Castro and Jackson, ; Metcalf et al ., ; Brockman et al ., ) and (2) a basis for stream assessment and design (Hey, ; USDA‐NRCS, ). Similar to hydraulic geometry curves (Leopold and Maddock, ), regional curves (Dunne and Leopold, ) are of the form:The variable A w represents drainage area (km 2 ), Q bkf is bankfull discharge (m 3 /s), A bkf is bankfull cross‐sectional area (m 2 ), W bkf is bankfull width (m), D bkf is bankfull mean depth (m), and the coefficients a , c , g , and j as well as the exponents b , d , h , and k are empirically derived values used to fit the data (Dunne and Leopold, ).…”

“…Developing a stream restoration design, such as through natural channel design techniques, is an iterative process that often begins by identifying the appropriate bankfull discharge and bankfull channel dimensions such as cross-sectional area, width, and mean depth in the riffles, predominately in perennial streams, with the aid of regional curves (Doll et al, 2003;Hey, 2006;USDA-NRCS, 2007). Regional curves relate these bankfull channel characteristics (i.e., dependent variable) to drainage area (i.e., independent variable) and can provide designers with (1) tools to help identify bankfull elevation in the field such as when bankfull indicators are absent or infrequent (Castro and Jackson, 2001;Metcalf et al, 2009;Brockman et al, 2012) and (2) a basis for stream assessment and design (Hey, 2006;USDA-NRCS, 2007). Similar to hydraulic geometry curves (Leopold and Maddock, 1953), regional curves (Dunne and Leopold, 1978) are of the form:…”

Bankfull Hydraulic Geometry Relationships for the Inner and Outer Bluegrass Regions of Kentucky

“…Metcalf et al [44] also found bankfull return intervals in these ranges for the northern regions of Florida. Such return intervals also agree with values found by stream restoration practitioners working in the Inner Bluegrass and Outer Bluegrass [59].…”

Bankfull Regional Curves for the Alleghany Plateau/Valley and Ridge, Piedmont, and Coastal Plain Regions of Maryland

“…Figure shows the MD Coastal Plain from this study compared to other Coastal Plain regions, including VA, North Carolina, and Florida (FL). Interestingly, the FL curves (Metcalf et al ., ) are the most different. FL receives more rainfall than the other regions, which may explain why the Northwest FL curve is the highest.…”